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Village Hope Technical Report 5

Aquaculture

Jonathan Bart26 August 2012

Standard VHTR disclaimer

Although we have made every effort to insure the accuracy of information in Village Hope Technical Reports most were written by students or by the President of Village Hope as way to learn about an unfamiliar topic. Use them to get an introduction to - or quick overview of - a topic, for ideas, and to locate references. But please do not treat them as authoritative accounts. If you want to you use some of the information, check the references and reach your own conclusions. We are always happy to hear from people with corrections, updates, or especially with offers to revise a VHTR or write a new

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.............................................................................................................................Summary 3..........................................................................................................................Introduction 4

........................................................................................................Sources of information 6.........................................................................................................PART ONE: SPECIES 8

..........................................................................................................................Introduction 8...................................................................................................................................Plants 8

......................................................................................................................................Fish 8........................................................................................................................Cyprinidae 9

........................................................................................................................Cichlidae 10.......................................................................................................................Other fish 11.....................................................................................................................Other animals 11

............................................................................................PART TWO: HATCHERIES 13.............................................................................................................................Facilities 13

........................................................................................Breeding stock (or brood stock) 18..........................................................................................Nutrition, fertilizers, and feeds 18

...........................................................................PART THREE: RICE-FISH SYSTEMS 23........................................................................................................................Introduction 23

...........................................................................................................Potential benefits 23..........................................................................Worldwide survey of rice-fish farming 31

............................................................................................Rice-fish farming in Africa 34.....................................................................................................................Conclusion 35

...............................................................................................................General approach 35..............................................................................................................Maturation time 35

.....................................................................................................................Polyculture 36....................................................................................................Design and construction 37

..........................................................................................................Refugia and dikes 37.............................................................................................................................Drains 39

..........................................................................................................Other information 39............................................................................................................Paddy management 40

........................................................................................................Water management 40.........................................................................................Azolla and other cover crops 40

........................................................................Stocking rates and species composition 41..............................................................................Fertilizer, feeding, and maintenance 41

.....................................................................Effects on fish of controlling pests of rice 42...............................................................................................................................Harvest 45

.......................................................................................................Methods and timing 45......................................................................................................Expected production 45

.................................................................................................................Case histories 46..........................................................................................................Other information 46

......................................................................................................Post-harvest processing 47...........................................................................................................................Marketing 47

.............................................................................................................Economic analysis 47

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..........................................................................PART FOUR: POND AQUACULTURE 48......................................................................................................LITERATURE CITED 49

Summary

Integrated Irrigation Aquaculture (IIA) has been widely practiced in rice paddies in many parts of the world for hundreds of years (Halwart and Gupta 2004). The methods are not yet widely practiced in West Africa but have been endorsed by many authorities (refs). IIA in rice paddies has three potential benefits:

1. Rice production per ha often increases, usually by ~10% and seldom >20%, despite the reduction in area devoted to rice production.

2. Income from sale of the species raised. With fish, the harvest is usually 400-800 kg/ha-yr in situations like ours. Less information is available about other species.

3. With proper methods, fish or other animals may reduce threats from certain diseases, especially ones transmitted by mollusks (xxx) and mosquitoes (xx) (what about black flies in channels that have flowing water?).

The major elements in an aquaculture strategy are:1. What species? Profits are usually higher with >1 species. Factors to consider in

selecting the species include tolerance to the environment (water temperature, dissolved oxygen, and turbidity), age at stocking (they must not feed on the rice seedlings), role and effectiveness in reducing disease, compatibility with the other species, maturation time (especially with 90-day rice), and market value. Candidate species (and examples) include many cyprinids (common and grass carp), many tilapia (Nile tilapia), many other fish (xxx), crustaceans (xxx), and other animals (ducks, xxx). Other species, especially Azolla, are widely cultivated as food for the fish or other animals and for the nutrients they add to the paddy.

2. Construction of paddies and other water control structures. Major issues include how high and wide to make dikes, how deep to make channels and other refugia for fish, whether to construct hatcheries and if so how, and what other structures are needed.

3. Production methods. Component issues include the hatchery strategy, other activities during maturation, when to harvest, post-harvest processing, and the marketing strategy.

4. Financial projections. The major costs are initial construction; labor during the hatchery stage; expenditures for fertilizer, other nutrients, herbicides, and pesticides; labor for harvest and post-harvest processing; and costs of selling the final products.

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Costs of fish production are estimated at $xxx/ha. Gross income is estimated at $xx so net income/ha is estimated at $xxx. Assuming profits, without aquaculture, of $4000/ha (see VHTR 19), aquaculture thus has the potential to increase our profits by xx% and to reduce risk from diseases present in the paddies to nearly zero. Substantial work may be needed to identify the optimal strategy but the benefits, especially disease reduction, seem well worth the cost.

Introduction

Aquaculture is the farming of aquatic organisms such as fish, crustaceans, molluscs, and aquatic plants (Wikipedia). It may be contrasted with commercial fishing which is the capture for sale of wild fish and mariculture which is aquaculture practiced in marine environments.

This report we discusses the potential of aquaculture to increase the earning power of people n our project area. We discuss speices (Part One), methods for hatcheries (Part Two), rice-fish farming (Part Three), and pond aquaculture (Part Four)

According to the FAO, aquaculture is the fastest growing food producing industry in the world (FAO 2000). De Silva and Davy (2009) compare aquaculture with fish production from “capture’ and show that aquaculture makes a major contribution in at least 9 countries, mainly in SE Asia but also in Chile (Table 1). They also report that production from aquaculture has increased rapidly during the past 10-15 years (Fig. 1).

Table 1. Contribution of capture fisheries and aquaculture expressed as percents of the GNP.Country Capture AquacultureBangladeshPR ChinaIndonesiaLao PDRMalaysiaPhilippinesThailandVietnamChile

1.91.12.41.41.12.12.03.72.2

2.72.61.75.80.42.62.14.02.6

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Fig. 1. Production of fish from aquaculture and commercial fishing (De Silva and Davy 2009 from Subasinghe et al. 2009).

Fig. 2. Aquaculture production in 2005 (De Silva and Davy 2009)

Aquaculture is concentrated in Asia (90% of production) with most of the rest occurring in Europe and Latin America (Fig. 2). Most of the production is fish (49%) or mollusks (23%), and nearly all (91%) of it is in freshwater systems (Fig. 3). Worldwide,

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Fig. 3. Production in 2005 by species and ecosystem (De Silva and Davy 2009)

aquaculture products command a low price (usually <$2 US/kg), and prices have been stable (or declined slightly) through the years. In temperate regions prices/kg are highest for salmonids whereas in tropical area they are highest for shrimp (De Silva and Davy 2009). The nutritional values of fish are well established (De Silva and Davy 2009), but they are not covered in this report since its purpose is to assess the economic potential of employing aquaculture in our project area.

Sources of information

Textbooks

Pilley, TVR and MN Kutty. 2005. Aquaculture: Principles and practices, 2nd edn. Blackwell.. $104 from Amazon. Both authors were with FAO. Authoritative, detailed, and comprehensive. Good on theory (e.g., nutrition). Good coverage of methods being used in developing countries. ~600 pp.

Parker, R. (coming Feb 2011). Aquaculture science. $155 from Amazon. Not yet released.

Lucas, JS and PC Southgate. 2003. Aquaculture: Farming aquatic animals and plants. Blackwell. $104 from Amazon. Edited volume. Editors from Australia. Contributors appear to be authorities. Comprehensive. 500 pp. Did not read sections.

Lekang, O-I. 2007. Aquaculture engineering. Blackwell. $191 from Amazon. Author is from Dept. of Math and Technology, Norwegian U of Life Sciences. Very detailed discussion of aquaculture equipment and theory behind it. 330 pp.

Timmons, MB and JM Ebeling. 2007. Recirculating aquaculture. $169 from Amazon. Was not able to look at ToC.

Stickney, RR. 2009. Aquaculture: an introductory text, 2nd edn.. $80 from Amazon. Was not able to look inside.

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Romanowski, N. ????. Sustainable freshwater aquacultures: the complete guide from backyard to investor. $76 from Amazon. Was not able to look inside but appears to be a popular book, not a textbook.

Other major references

FAO (2001), Integrated agriculture-aquaculture: a primer 157 pp. Oriented to extension agents so not much lit. cited and lots on extension methods, but still an excellent source for practitioners.

Halwart and Gupta (2004), Culture of fish in rice fields, 83 pp. Detailed account of rice-fish methods; many details and extensive literature review.

Halwart and van Dam (2006), Integrated irrigation and aquaculture in West Africa, 197 pp. Conference proceedings. Much more policy and community development; less on the mechanics of rice-fish farming (but may warrant more attention)

Nandlal and Pickering (2004). Tilapia hatchery operation. 41 pp. Written for residents of the Pacific Islands but a good overview of methods (not examined yet)

Ngugi (2007) Fish farming manual for Kenya. Excellent “how-to guide”.

Journals Aquaculture (Elsevier) Aquaculture research (Wiley)Reviews in Aquaculture (Wiley)

Organizations

Asia-Pacific Fishery CommissionThe World Fish Center, GPO Box 500, 10670 Penang, MalaysiaAquaculture Compendium (http://www.cabi.org/ac/) – online clearing house of

worldwide aquaculture information

At the time of the 2006 conference the FAO had an Inland Water Resources and Aquaculture Service and WARDA had an Inland Valley Consortium of West African countries including SL.

Some of the major people with expertise in aquaculture are (contact into in People-Progams-Projects.doc):

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PART ONE: SPECIES

Introduction

This chapter discusses the animals and plants that are raised during aquaculture operations. We identify the species likely to be most important in our project, the roles they could play, and their habits and requirements.

Plants

The aquatic fern, Azolla, is often grown in rice paddies both to add nitrogen and as food for fish. Chn (1995 cited in Halwart and Gupta 2004) described a trial in which the yield of fish was 70% higher with Azolla than without it.

Fish

Numerous factors warrant consideration in selecting fish to raise in paddies or ponds:

1. Tolerance for shallow water, high turbidity, low oxygen, and high and variable temperatures (Halwart and Gupta 2004, p. 24).

2. Ease with which fingerlings can be produced3. Growth and maturation times4. Biomass and desirability as a human food5. Efficacy in reducing mosquito and snail populations6. Feeding behavior (surface, water column, bottom; species consumed)

Worldwide, the most widely farmed fish are Cyprinus carpio, Oreochromis niloticus, and Barbodes gonionotus (FAO 2001 p. 117) but a great many other species are farmed commercially. Halwart and Gupta (2004) provide a long table of fish (and crustaceans). The only ones from West Africa are Tilapia melanopleura, Oreochryomis niloticus and Beterotris niloticus, all reported from Cote d’Ivoire.

Weimin (2010) provides an interesting account of how the government in China studied aquaculture and then introduced new species which increased profits. The traditional species in rice-fish systems were mainly carp and tilapia but they had low value in markets. It was found that equal or only slightly lower production could be achieved with higher-value species (Table 2). Weimin He concludes “introduction of the high valued species significantly improved the economic return from rice-fish farming.” This example indicates the potential value of considering species that may not be used commonly at present but that have high market value.

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Table 2. Traditional and introduced species in rice-fish systems of China.

According to Bentz (2006), in a project that I think was in Core d’Ivoire,

The culture system was based on the polyculture of tilapia (Oreochromis niloticus)and Heterotis niloticus. In addition, many wild catfish existed in many bas-fonds, mostly Clarias anguillaris and Heterobranchus isopterus. In Côte d‘Ivoire, Chinese carp (Ctenopharyngodon idella) was sometimes also cultured. Population densities were adjusted depending on the fertility of the area, and a carnivorous fish (generallyHemichromis fasciatus) was added to regulate tilapia populations which are quite prolific.

Her description of the project suggests that two NGOs who managed it were essential, but they depended on outside funding which was eventually withdrawn.

See http://www.worldfishcenter.org/wfcms/HQ/article.aspx?ID=108, the WorldFish site for information on specific species.

Cyprinidae

Cyprinus carpio (common carp) – bottom feeder; tolerates poor water qualty, exellent growth in most rice fields, high susceptibility to predation and thus survival often poor (FAO 2001). Controls golden apple snails (FAO 2001, p. 117).

Ctenopharyngodon idella (grass carp) – used in pens in Cote d’Ivoire (Brugere 2006). Native in Asia.

??? (silver carp) – column feeder (FAO 2001)

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???? (Chinese carp). Poor growth in rainfed fields; do better in deep (50 cm) water (FAO 2001).

??? (Indian major carp). Poor growth in rainfed fields; do better in deep (50 cm) water (FAO 2001).

Aphanius dispar (Arabian killifish) - feeds on mosquito larvae and reduced malaria in Ethiopia (Fletcher et al., 1992, cited in Brugere 2006).

Barbodes gonionotus (silver barb) – surface feeder; usually excellent survival (even fry) in rice fields, less tolerant of poor water quality than common carp and Nile tilapia; does not grow well in very shallow water (FAO 2001).

Cichlidae

This family is native to Africa. It includes three genera important in fish farming. Oreochromis, Tilapia, and Sarotherdon. For breeding, they form groups but males defend individual territories and build nests. Both males and females may breed with multiple partners. Eggs are fertilized in the nest. Parental care varies among general.

Oreochromis. One of the three cichlid genera important for fish farming. Mouth-brooders (females). Widely used for aquaculture. The three most important species are O. niloticus, O. mosaambicus, and O. aureus.

O. niloticus (Nile tilapia, formerly Tilapia niloticus or Sarotherodon niloticus) –reddish to white. Rasovo and Auma (2006) quote Balarin and Hatton (1979) as saying the optimum water temperature is 29-32 C. Tolerates environmental extremes well, reproduces frequently which can cause over-stocking and poor growth; some farmers do not like taste (FAO 2007).

Nile tilapia are bottom-feeding omnivores consuming plankton, detritus, small fish, and aquatic plants. Females produce 100-500 fry per breeding effort and are most fecund when less than one year old. Hatch occurs in 6-10 days and the fry remain in the female’s mouth for another 4-7 days. Fry then begin to leave the mouth but may return when threatened. The female does not feed during this period. Nile tilapia become sexually mature at 3-5 months (150-200 g) and can then spawn every 4-6 weeks. They will spawn year round if temperature is above 22 C. 25-30 C is considered ideal.

O. mossambicus (Mozambique tilapia) – bluish.

O. aureus (blue tilapia) - dark color.

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Tilapia. The second of the three cichlid genera important for fish farming. Eggs are guarded at the nests.

Tilapia guineensis – used in pens in Senegal (Brugere 2006). African coastal waters but also sometimes far upriver, thoughout West Africa from the Senegal river south. Said to feed on “shrimp, bivales,plankton and detritus” (http://www.fishbase.org/summary/SpeciesSummary.php?id=2488. Biology and culture reviewed by Campbell, 1987, at http://www.fao.org/docrep/field/003/AC165E/AC165E00.htm. He comments that the species has not been widely used (in 1987) for aquaculture but has some desirable traits.

Sarotherdon. The third of the three cichlid genera important in fish farming. mouth brooders (either sex).

Sarotherodon melanotheron (black chin tilapia) – used in pens in Senegal (Brugere 2006). In habitat fresh to brackish water; demersal often in muddy water.

Other fish

Astatilapia callistra - feed on mollusks (Chiotha 1995 cited in Brugere 2006).

Hemichromis fasciatus (banded jewelfish) – used in pens in Cote d’Ivoire (Brugere 2006). Widely distributed in West Africa.

Trematocranus (Maravichromis) anaphyrmis - feed on molluscs (Chiotha 1995 cited in Brugere 2006). Not found in Google.

T. placodon - feed on molluscs (Chiotha 1995 cited in Brugere 2006).

Heterotis niloticus (African bony tongue) - used in pens in Cote d’Ivoire (Brugere 2006). Widely distributed in West Africa.

Channa sp. (snakehead) Very palatable (FAO 2001)

Clarias sp (walking carfish. Very palatable (FAO 2001). Controls golden apple snails (FAO 2001, p. 117).

Trichogaster pectoralis (snakesin gourami). Promising results in a few rainfed ricefields; broodfish, not seed, should be stocked; more work needed (FAO 2001).

Other animals

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In the SE US, adult crawfish (Procambarus clarkii) are added to rice paddies in June when rice are 10-25 cm tall. The crawfish reproduce and their offspring mature after harvest when the fields are re-flooded. Various other crustaceans are also grown in rice paddies with or without fish. Clams, frogs, and turtles are also harvest in rice fields, though little evidence exists that they are stocked.

Ducks have often been raised in rice paddies for both meat and eggs and because they eat dangerous invertebrates, especially molluscs. Syamsiah et al. (1993 cited in Halwart and Gupta 2004) reported that 100 laying ducks in a one-ha fish pond laid >17,000 eggs/year. The ducks presumably also added a substantial amount of fertilization to the paddies. Given our short flooding period, and that ducks would presumably damage small plants, I question whether they would be feasible for us.

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PART TWO: HATCHERIES

This chapter discusses breeding fish and rearing the young until they are ready for sale or release into paddies or ponds. It includes transport of fingerlings. Timing of release and stocking density are discussed in the chapters on rice-fish farming and pond aquaculture. We do not discuss rearing of species other than fish.

Many authors have commented that lack of access to fingerlings is a major problem for fish farmers in Africa (Ngugi 2010) and elsewhere (refs.). A contrary view was expressed by Sanni et al. (2006, p. 76) who visited four countries in West Africa and commented that fingerlings suitable for aquaculture, especially Oreochromis niloticus, were widely available. We do not know of any fish farms near our project area and think it would be unwise to assume that fingerlings will be available. We therefore consider it essential that hatchery operations be included if we establish an aquaculture program.

A few terms warrant definition. “Fry” are fish soon after hatching but the term is apparently not defined precisely. “Fingerlings” are 1-3 g fish that have completed a “nursery” phase and are ready for grow-out ponds. “Grow-out” means development until sale. A “hatchery” is a facility to produce fry and fingerlings for grow-out.

Facilities

The hatchery must include facilities for maintaining adult fish (broodfish) for breeding; spawning areas (ponds, tanks, or hapas); containers in which the fish spawn, incubate the eggs, and brood the young fish (fry); and containers in which the young fish grow until they are large enough to survive in a paddy or pond.

Authors describing hatcheries emphasize that water quality and quantity is one of the most important considerations in hatchery design (Ngugi 2007). In our case, using rain water or ground water are both feasible and seem desirable to avoid undesirable organisms (and make filtration unnecessary) and pollution. Xxx (2005, p. 93), however, cautions that well water often has excess gas which can cause “gas bubble disease”. The gas can be removed by adequate aeration. If excessive water temperatures are a potential danger, being able to mix add water easily may be desirable (though I suspect water temperatrue equilibrates to air temperature fairly quickly).

Disolved oxygen levels should not drop below 3-4 ppm (= mg/l) for carp (xxx 2005). In hatcheries, this is usually easy to accomplish by exposing water to air as it enter the containers or by using simple aeration devices.

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If insufficient water is available, water may have to be purified and re-circulated. Numerous methods exist for this process but I assume we will have a small enough operation, and ready access to fresh water when needed.

The basic equipment needed in a hatchery includes: taknks for brood stock; implements for collecting and handling breeders, for striping, and fertilization; spawning tanks where necessary, jars, troughts, tanks or other containers, net cage or “hapas” (mesh cloth tanks) forincubating and hatching fertilized eggs; food dispensers; larval rearing tanks and aeration systems (xxx 2005, p. 95)

For brood tanks, see sec. 6.2.

For large finfish, “special hammocks” have proved very efficient. See Ch. 16 for methods for stripping and fertilization.

Spawning tanks in the open may be built of concrete with adequate arrangements for water circulation.

Different types of incubators ar used for hatching fertilized eggs, ranging from improvised earthen and polyethylene jars to sophisticated batters of jars and troughs. The method depends on the species, size of eggs and magnitude of operation. The general principle is the provision of regulated flow of good quality water, of the required temperature, for the development and hatching of the fertilized eggs and prevention of infections that will affect the hatching rate.

Troughs made of wood, concrete, aluminum, plastic or fiberglass are commonly used. Size varies by ave may be 3m x 0.5 m x 0.25 m. Generally screen at the intake to prevent detrius and at the outflow to exclude the larvae. Egg baskets may be fitted in the tray that permit hatchling to fall thru but not eggs. Water is forced up through the perforations.

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Fig. xx. Simple hatchery troughs made of wood (left) and fiberglass and aluminum trough in a modern carp hatchery in Hungary (right)..

Special glass jar incubators (known as Zuger jars, Weiss jars or Zug-Weiss jars and MacDonald jars) and plexiglass or other plastic funnels as well as less expensive sieve-cloth funnels and even earthen jars are used for incubating non-adhesive eggs. Even in cases like the common carp, these devises can be used after removing the sticky layer.

Different types of larval rearing trough, tanks and pools are in use and some types are readily available from manufacturers. The basic requirements are proper circulation and drainage of water to keep them well supplied with clean oxygenated water and prevent accumulation of waste products.

Fig. Glass jar incubators

Fix. Plexiglass funnel incubators

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Fig. xxx. Sieve-cloth incubators for carp eggs in Nepal.

Fig. xxx. Earthern jars for hatching carp eggs in Nepal.

Fig. xxx. Hapas (cloth tanks) for rearing carp larvae in India.

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Fig. Double hapas for hatching carp eggs.

For rearing carp larvae, circular cement pools build on the ground, are commonly used. For hatching and larval rearing in Indian carp culture, meshed coth tanks (hapas) fixed on the pond bottom by means of stakes are widely used. It is common to have double tanks. the inner smaller tank with fine mesh holds the fertilized eggs for hatching. The hatched larvae fall into the outer larger cage, leaving behind the egg shells and debris. The inner cage can be removed easily after hatching. Rectangular cement cisterns, with an adequate water supply and drainage, are also used in many places.

Although some of the simple and improvised hatchery systems such as the carp hatcheries in China and India are built in the open, modern hatchers are installed indoors (which seems essential for us given the rains). In some cases the larval rearing may be carried out in tanks, pools or ponds outdoors, but where water temperature has to be controlled they are generally provided with at least a protective roofing.

Many different lay-outs exist for hatcheries. A chief consideration is getting water where it is needed. Xxxx (2005) recommends that supply lines be able to deliver 1.5 times the expected maximum needed amount. An elevated tank may be desirable for us.

I order to save space and reduce the use of water, it is possible to stack the troughs or trays used for incubation and larval rearing one above the other. Battery incubators are available for manufacturers. They consist of vertically stacked troughs each having an egg tray and a cover. Each trough can be pulled out separated for inspection. The water flow will pass downwards through each vertical trough stack, trickling through each one from top to bottom.

Laboratory space is also needed for routine tests and examinations.

Rice paddies provide excellent nurseries for fish, especially given the short time they are flooded. Stocking densities can be “considerably higher than 3000 fry/ha” (FAO 2001).

Nurseries are typically cover 200-500 m2 (FAO 2001, p. 137). FAO (2001, p. 137) recommends that after the nursery has been dug and allowed to dry, 5-6 kg of lime should

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be added for each 200 m2 to help release nutrients and kill pathogens. The nursery should then be left for two weeks after which it is filled and fertilized. FAO (2001, p.

Breeding stock (or brood stock)

Acquire brood stock from the wild or through purchase that are healthy and in prime breeding condition (e.g., about a year for catfish and tilapia and >100 g for tilapia and 0.5-1 kg for catfish).

Nutrition, fertilizers, and feeds

Carbohydrates are the most abundant and least expensive source of energy in fish foods. Metabolizable energy is up to 3.8 kcal/g for sugars, 1.2-2 kcal/g for starch, and close to zero for cellulose. Fish feeds for warm water species often contain up to 30% carbohydrates.

Protein is the main source of nitrogen and essential amino acids in animals. In nature, carnivorous fish consume diets with ~ 50% protein. They excrete waste N and catabolize it for energy. High protein diets are thus not harmful but, since protein is expensive, prepared fish diets are usually lower in protein than the wild diet. The energy value of protein in fish is about 4.5 kcal/g (which is higher than the value in mammals or birds).

Proteins requirements for growing High-growth diets have been determined for many fish. The requirements are highest in the young fry and decrease as size increased. For maximum growth, young fish require diets with 40-60% protein. Some fish, including s

Table xx. Dietary protein and energy levels resulting in highest growth rates in various teleosts (in % dry diet).

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salmonids continue to require 40-60% protein but other species (e.g., milkfish) rapidly switch to a diet of algae containing 10-20% protein.

Although it is common to believe that herbivorous fish require smaller amount of protein for optimal growth, xxx (2005) states that the literature does not support this view and that carp, for example, require the same high level for optimal growth as other species. Herbivorous species, however, may have substantially more ability to digest complex carbohydrates than carnivorous species.

Amino acids

Ten amino acids are considered essential in fish, crustaceans, and mollusks (Table xx). Recommended levels for several species are shown in Table xx.

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Table. Requirements of essential amino acids in g/kg dry diet.

Tablee xxx. Amino acid requirements as a percentage of protein (note tha sums are far less than 100%).

Lipids and essential fatty acids

Lipids aree fat-solutble compounds that occur in tissues of plants and animals. They include fats, phospholipis, sphingomyelins, waxes, and sterols.

Fats are the fatty acid esters of glycerol and are the principal form of enery storage. They contain an estimated 8.5 kcal/g of metabolizable energy, more than any other biological product. Natural diets may contain up to 50% fat.

Phospholipids are the esters of fatty acids and phosphilic acid. They are the main consitutuents of cellular membranes. Sphingomyelins are present in the brain and nerves.

Vitamins

Vitamins are a chemically diverse groups of organic substances that organisms do not synthesize or synthesize too slowly to meet demands. Information on requirements for

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dietary vitamins is scare and concern is probably not warranted if the fish are fed natural diets. Vitamins in prepared diets are usually sufficient ot meet needs though this should be confirmed.

Minerals

Minerals are required by all animals for various functions including formation of skeletal tissues, respiration, digestion, and osmoregulation. Of the 26 naturally occurring essential elements described for animals, only 9 have been shown to be required for finfish. Water generally contains abundant miners so supplementation is rarely needed.

Broodstock and larval nutrition

It is thought that larval and broodstock requirements are similar to the requirements for optimal growth. In general, the diet should be high in protein with sufficient amounts of the essential amino acids.

137) says to check whether sufficient food is present by filtering 50 liters of water through a fine mesh net or cloth into a 2.5-cm diameter “specimen tube” but it doesn’t say how to evaluate the results. It also says that if a hand submerged up to the elbow is no longer visible, then the plankton level is probably sufficient.

One day before adding hatchlings, treat the nursery with 80-100 g of insecticide such as Dipterex to kill the aquatic insects. Then stock with 60-70,000, 4-5-day-old hatchlings/200 m2 that are uniform in size and vigorous. They should be released in morning or late afternoon. Release then by opening the bag they are in for a few minutes before letting them out of the bag so that the temperature will equilibrate.

Common feeds include rice bran or straw (the straw is not eaten directly but supports flora and fauna that the rice consume (FAO 2001), and termites (which should first be drowned to avoid injury to the fish). Also mulberry, banana, Leucaena leaves; bat or livestock dung; coconut oil residues (FAO 2001). Dead animals should generally not be added to nurseries because they contaminate the water. FAO (2001, p. 139) recommends the following diet: oil cake (soya beans, mustard, etc.), rice or wheat bran and fish meal in the ratio 5:4:1. Add this mixture several times per day for a total amount of 200 g per day. They add that fertilization is needed but not elaborate on kind or amount needed. the nursery should be checked frequently for green algae (which indicates excess food) or invading animals such as snakes or frogs. Growth rates should also be monitored as an additional indication that conditions are suitable.

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Harvest the fingerlings after 30 days (?) with a net in the morning or late afternoon. If they are going to transported any distance, hold them in a cistern or other container for 3-4 hours so they have time to empty their guts (and thus avoid contaminating the travel container). Transport them in oxygenated plastic bags.

To protect fertilized eggs against infectious diseases dip them for 1 minute in a 50% common salt solution prepared at the site of stocking (FAO 2001).

Fish should be transported in “oxygenated plastic bags” in the morning or evening when temperatures are lower (FAO 2001). They should be transported immediately after removal, not shaken, and kept out of direct sunlight. For release, the bag should be set in the water for several minutes so the water temperature will equilibrate before the bag is opened.

With normal sized fry (???) “rice should also be well-established with 2-3 tillers out before fingerlings or large fish are allowed into the field” (FAO 2001). This is usually 1-3 weeks after transplanting or 4-6 weeks after direct seeding. Small fry (2.5 cm) can be stocked immediately after rice are transplanted.

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PART THREE: RICE-FISH SYSTEMS

Introduction

We use “rice-fish systems” to mean growing rice and fish or other animals concurrently. Rotational systems refer to growing them sequentially. We do not discuss this approach, even though it is said to yield more fish (Halwart and Gupta 2004), because it requires maintaining flooded fields during the dry season which we do not currently know how to do. We also do not discuss the well-known nutritional benefits of fish because the main purpose of this report is to assess the economic consequences of adding fish to rice paddies. Ricee-fish farming has been tried in many parts of the world (Fig. 4).

We begin this Chapter by discussing the three major potential advantages of adding fish to rice paddies. Then we discuss rice-fish farming methods around the world. Finally we review recommendations for rice-fish farming in Africa and assess the potential value of this method in our project area.

Fig. 4. Area with significant areas in rice-fish cutlure (Halwart and Gupta 2004, p. 56).

Potential benefits

Three potential economic benefits of adding fish to rice paddies have been identified: (1) production of animal (fish) protein that can be sold, (2) increased production/ha of the rice due to beneficial effects of the fish on rice plants, and (3) reduced potential human disease because fish consume the primary disease vectors,

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mosquitoes and certain snails (Halwart and Gupta 2004; Brugere 2006, many other references). The potential disadvantages are that rice production is reduced, by more than the value of the fish produced, due to the practices needed for fish production, and that these effects are not sufficient offset by benefits due to disease reduction.

Fish for the market

In this section we review production quantities and market value.

Improved rice production

Fish probably produce more healthy rice plants in a variety of ways. They may feed on weeds, especially young ones, and bottom feeders stir up the sediments that weeds cannot sprout Gupta et al. (1998 cited in Halwart and Gupta 2004, p. 42). According to Halwart and Gupta (2004, p. 41-42), farmers in Bangladesh report significant reduction of weeds by B. gonlonotus and C. carpio. Halwart and Gupta (2004, p. 42) also state in “In China, fish have been found to be more effective in weed control than either manual weeding or use of herbicides.” Care is needed however in selecting the species – if weed control is a major objective – because species are not all equal and >1 species may be needed. O. niloticus, for example, is not generally regarded as effective in weed control (though it does consume blue-green algae). Weed control by fish can be impressive, however. Wu (1995 cited in Halwart and Gupta 2004, p. 42) describes a case in which addition of fish to a field with 101 kg of weeds reduced the weed load to 20 kg in five weeks, while weeds in a nearby field with no fish increased from 44 kg to 273 kg. Species known as effective weed controllers include O. mossambicus, Tilapia zilli, B. gonlonotus, and Trichogaster pectoralis (Khoo and Tan 1980, cited in Halwart and Gupta 2004, p. 42).

Fish also affect invertebrate populations though the effect is complex and may be either positive or negative (FAO 2001, p. 118-119). Gupta et al. (1998, cited in Halwart and Gupta p. 42) reported a study in Bangladesh in which populations of useful insects (lady beetles, spiders, damsel flies) were 5-48% higher in rice-fish paddies than in rice only paddies 10-12 weeks after transplantation, but the converse occurred later on. Despite this effect of fish on beneficial species, however, pest infestation levels were 40-167% higher in the rice-only paddies during all stages indicating that the fish were benefiting rice by feeding on the harmful insects. According to Halwart and Gupta (2004, p. 42), “rice planthoppers and leafhoppers usually rest on the middle or lower parts of the rice plants to suck plant juices during the day and climb to the upper part of the rice plant to feed at night or in the early morning. C. carpio and C. idellus over 6.6 cm in length were found to be effective in reducing planthoppers and leafhoppers, respectively (Xiao 1992).” They say that C. idellus is the most effective predator on hoppers, followed by C. carpio and O. niloticus.

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To help fish reduce insects, FAO (2001) recommends submerging the rice for three hours so fish can feed on the insects (works only before rice height exceeds dike height) or pulling a rope across the rice to dislodge insects and make them more available to the fish (works only prior to the “booting” stage.

Data in Halwart and Gupta (2004, p. 43) from Yu et al. (1995) suggest that grass and common carp, and Nile tilapia, reduced planthopper nymphs by 20-50%. Thus, complete control was certainly not achieved. Similar results are reported from several other studies in Halwart and Gupta (2004, p. 43). Density in the control plots in the Yu study were 6000-8000. In contrast, Tuan (1994), however, reported a case in which hopper density in the paddies without fish were “hundreds of thousands” whereas it was only 3,800/m2 in the paddies with fish. Thus, fish may be effective in preventing very high infestations.

Fish may also control snails that harm rice, especially the golden apple snail, native to Latin America but now an important pest across much of Asia. Efforts wsere first made to control them with molluscicides but they proved hazardous to humans and livestock (and became ineffective?). Control by fish, especially carp, was studied extensively in the Philippines by the Asian Rice Farming Systems Network (ARFSN). In laboratory settings, common carp were found to consume 150-300 juvenile snails/day and to feed on larger snails at lower rates. This work led to field trials, identification of C. carpio as a particularly effective control agent and O. niloticus, B. gonlonotus, and O. mossambicus as other species with promise as control agents. According to Halwart and Gupta (2004, p. 45) FAO endorsed biological control as the most promising method for control of apple snails, but they do not present any information on how effective the approach has been.

Fish may also help control disease in rice paddies. For example, Xiao (1992) and Yu et al. (1995), in Halwart and Gupta (2004, p. 45), reported that C. idellus reduced the incidence of rice sheath blight disease. The mechanism was uncertain but may have involved removal of infected, bottom leaves. Once the disease spread above the water line, it was unaffected by fish.

A final benefit of stocking fish is that less fertilizer is often needed by the rice. (Wu 1995, cited in Halwart and Gupta 2004, p. 23). Bottom feeders such as common carp disturb and aerate the upper layer of soil. This increases aerobic decomposition and releases inorganic nutrients making them available to the rice. In addition, fish consume weeds and excrete the nutrients which then become available to the rice. Li et al. (1995, cited in Halwart and Gupta 2004, p.24) reported that 23% more fertilizer was required in fields without fish compared to those with fish.

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Although understanding how fish affect weeds, invertebrates, and disease is useful in various ways, the critical question is how rice yield compares with and without fish. Halwart and Gupta (2004, p. 36-39) carried out a careful review of the literature on this issue and concluded that production is usually slightly higher (most commonly by 10%) even though fish production decreases the land available for rice (Fig. 3).

Fig. 4. Effect of fish on rice yield based on data from China, India, Indonesia, the Philippines, and Thailand, 1977 to 1992 (Halwart and Gupta 2004, p. 39).

Disease reduction

Fish (and maybe other animals) may reduce the risk to humans of diseases present in paddies. The diseases common in West Africa and spread via rice paddies are yellow fever, malaria, and dengue fever spread by mosquitoes and schistosomiasis spread by snails. Onchocersiasis (river blindness) is spread by black flies but they breed in fast-flowing streams and rivers so they would not colonize paddies. It seems unlikely that they would colonize canals delivering water to paddies because flow would be intermittent. Nonetheless, better information on this issue would be beneficial. See VHTR 12, Diseases, for a detailed discussion of the diseases that may be propoagated in rice paddies.

Oreochromis niloticus is known to feed on mosquito larvae (Jenkins 1964, Asimeng and Mutinga 1993, Kusumawathie et al. 2006). Fry <15 cm long pursue and consume immature mosquitos. Larger fry feed on macrophytes and thus are not effective in mosquito control (Trewavas 1983, el Safi et al. 1985).

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In a controlled study in Kenya, Howard et al. (2007) reported that Tilapia niloticus reduced Anopheles gambiae and A. funestus by <94% and reduced culicine mosquitoes by <75%. Their detailed data (Fig. 5) show persistence and occasional short increases in mosquito populations (especially in pond D) but the fish clearly did reduce populations dramatically (e.g., as shown when fish were introduced to pond A).

Fig. 5. Effect of O. niloticus on mosquitoes (from Howard et al. 2007).

Halwart and Gupta (2004, p. 42) describe a study (WHO 1980 in Pao 1981) in which the combination of Gambusia and common carp reduced anopheline and culicine larvae by 90% and 70% respectively. They summarize other evidence on the mosquito-control capacity of fish as follows:

Field surveys in China indicate that mosquito larvae densities in rice fields with fish were only 12 000·ha-1 as against 36 000·ha-1 in rice fields without fish (Wang and Ni 1995). In other studies mosquito larvae were observed in only one of nine rice fields stocked with fish, being completely absent in the other eight, whereas in other rice fields not stocked with fish, the density of mosquito larvae ranged from 32,000 to 128,000·ha-1. In Indonesia, fish were found to be even more effective in controlling

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mosquitoes than DDT. After five years of fish culture in rice fields, malaria cases decreased from 16.5% to 0.2% in a highly endemic area for malaria (Nalim 1994). In a control area using DDT the malaria prevalence remained steady at 3.4% during the same period.

In summary, there seems to be clear evidence that fish of many – though not all – species may substantially reduce, or even eliminate, mosquito larvae. Care is needed to insure that the right kind of fingerling (species, size) are present throughout the growing season, and the early period, before fingerlings are released into the paddies may be problematic.

The evidence on whether fish can control snails that serve as hosts for schistosomiasis (biharzia) is less clear. Halwart and Gipta (2004, p. 52) discuss this issue but present results from only one study in china in hwich Haplochromis mellandi and Tilapia melanopleura stocked at 200 and 300 fish/ha were said to control “the majority” of snails (species not identified). Halwart (2001, cited in Halwart and Gupta 2004, p. 52) concluded that significant control could occur.

Schistosomiasis is caused by several species of blood fllukes in the genus Schistosoma. The species in Sierra Leone are S. mansoni and S. haematobium. The hosts for S. mansoni include snails in the planorbid snail genus Biomphalaria (B. pfefferi and perhaps B. cammerunensis in Sierra Leone). The hosts for S. haematobium include snails in the genus Bulinus (B. globosus and probably B. umbillicalus and B. jousseaumei in Sierra Leonre) respectively.

Biomphalaria snail are usually controlled using molluskicides but this is expensive, resistance can develop, and the pesticides may harm fish or other desirable organisms in the water. Control using fish is often mentioned. A report by the FAO (Kutty 1987) states that fish are one of the “best methods” for controlling undesirable snails. They cite 7 studies none of which I’ve been able to obtain. A review by Slootweg et al. (1994), however, said that in general fish do not effectively control of snails though they may be of some value in this regard:

The use of molluscivorous fish for biological control of snail intermediate hosts of schistosomiasis is a regularly reappearing theme in the literature on schistosomiasis control. The effectiveness of this control method has not yet been demonstrated, and conclusive field evidence is lacking. In this article the literature on snail control by fish is critically reviewed. Special attention is paid to the cichlid fish Astatoreochromis alluaudi that has been used in well-documented field trials in Kenya and Cameroon. After some small initial success, after a longer period the fish appeared to be ineffective in snail control. Moreover, the fish reproduces at a pace too slow to be of use in large-scale biocontrol trials. Laboratory observations on foraging behavior and anatomy of the fish give

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essential cues to explain the failure of the fish in snail control. An observed reduction in the fishes' pharyngeal jaw apparatus, used to crush snails shells, results in a lower profitability of snails. As predicted by a simple foraging model, the prey preference of the fish shifts towards other more profitable prey items, such as benthic and pelagic macrofauna. Although eradication of snails by fish will not be feasible in most cases, the role of natural predators of snails cannot be neglected, and may still be of importance in integrated control efforts.

In randomized trials with three replicates in Bangladesh, Frei et al. (2007) tested carp only, tilapia only, and carp-tilapia combination in rice fields and found that the fish yields (kg/ha) were 586, 540, and 257 respectively. In a second trial, all with carp-tilapia mixtures, feeding (urea) levels were varied as followed (a) 4x maintenance level (ML) early to 2x ML late, (b) 2x ML throught, (c) no feeding. Fish yields were 935, 776, and 515 respectively. They say that the rice production was “controversial” but was highest with “regular” urea feeding.

Ducks have also been suggested for controlling Pomacea snails(Sin Teo 2001). At 5-10 ducks/ha, snail density was reduced from 5/m2 to <1/m2 during 1-2 months. The ducks could be released into transplanted rice when the plants were 4 weeks old. With 90-rice, and assuming the field was drained at day 75, this means the ducks would be in the rice paddies for about 1.5 months.

Control of Biomphalaria snails was achieved at two sites in Ethiopia by spraying soap berry and giving it to local residents as a soap powder (Abebe et al. 2005). Pomacea snalils have been shown to consume Biomphalaria glabrata egg masses (Paulinyi and Paulini 1972). Extracts from many other plants have been used to control Biomphalaria. Drawdown and drying of ponds was suggested by Jobin (1970) but he did not have enough information to suggest the length or frequency of dry periods.

Walmart and Gupta (2004, p. 40) cite Waibel 1992, Cagauan 1995, and Halwart 2001a, b, 2004a for information on snail predation by fish.

Detaled knowledge of the life history of the hosts for these diseases is needed to design effective strategies for controlling them.

Balusubramanian et al. (2007, p. 117-118) warn that the risk of infection by diseases, especially malaria and schistosomias, may be higher for people working in wet rice fields. They seem to say that the risk of malaria infection is small in areas where exposure to malaria is already high including in Western Africa. Schistosomias is common where people are in contact with snail-infected water, which is usually in slow-

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moving rivers and streams and vegetation along the banks of such water bodies. They state (p. 118) that “timely treatment of infected people with a single dose of an appropriate anthelminthic drug will control the disease effectively in all areas, including wetland rice areas (WARDA, 1999)”.

Summary and conclusions

The third potential benefit of adding fish to rice paddies, reducing the threat of human diseases, is hard to evaluate economically. The first two potential benefits, however, increased rice production and sale of fish, can be analyzed economically. Halwart and Gupta (2004, p. 49) tabulated costs, income, and net returns in rice production, with and without fish, in all of the locations they could find (Table 2). Returns from the rice-fish systems were higher in every case. The average difference was about $400 using 1987 dollars or about $800 adjusting for inflation. Fish-rice systems earned roughly twice as much as rice only systems. The only exception was in Thailand where individual costs

Table 2. Comparison of costs, income and return to labor with and without fish (Halwart and Gupta 2004, p. 49). All figures are in USD/ha in 1987.

Country

Rice onlyRice onlyRice only Rice-fishRice-fishRice-fishRice-fishRice-fishRice-fish Differ-ence

(fish-no fish)

Ratio (fish/

no fish)Country

In-come

Ex-penses

Net income

IncomeIncome ExpensesExpensesExpensesNet

income

Differ-ence

(fish-no fish)

Ratio (fish/

no fish)Country

In-come

Ex-penses

Net income rice fish rice fish total

Net income

Differ-ence

(fish-no fish)

Ratio (fish/

no fish)

Bangladesh 690 326 364 749 195 302 72 374 570 206 1.57Bangladesh 444 137 307 464 183 121 31 152 495 188 1.61China 562 158 404 559 864 131 202 333 1090 686 2.70China 405 588 183 1.45Indonesia 1663 770 893 1518 490 621 122 743 1265 372 1.42Philippines 700 469 231 674 126 506 294 63 1.27Philippines 757 390 367 1098 607 322 242 564 1141 774 3.11Philippines 1579 1143 436 2077 1126 1860 1343 907 3.08Thailand 160 120 -40 0.75Vietnam 268 334 66 1.25Averages 914 485 384 1020 513 299 134 647 724 341 1.82 and incomes are not available but the net income from both rice only and rice-fish systems was very low. The average difference in net incomes was $341, or about $700 in 2010 dollars. Since these data were collected in the 1980s, rice production and profits/ha have increased substantially whereas fish production/ha has increased more slowly. The ratio of net incomes thus may have changed substantially. The difference in net incomes, however, should be much more similar. It would be higher than in the 1980s because fish lead to an increase in rice (of about 10% based both on data summarized above and on income derived from rice in Table 3). Thus, a net increase in profits/ha of about $1000/ha

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seems plausible, and it might be higher using aquaculture methods not available in the 1980s. Projected profits from rice in our area are now about $4000 (see VHTR 19) so this would represent a 25% increase in profits – a substantial gain. In addition to the health benefits, other benefits include providing both employment and on-the-job training for local residents. There thus seems to be clear evidence that adding fish to irrigated rice paddies will result in both economic and non-economic benefits.

Worldwide survey of rice-fish farming

Given the substantial potential advantages of adding fish to irrigated rice paddies, it might seem likely that rice-fish farming would be widespread. It is therefore instructive to consider where rice-fish farming has and has not become widely established around the world. The following accounts are from Halwart and Gupta (2004) unless otherwise noted.

In China, rice-fish farming was widely supported starting in the mid-1950s. During 1960s and 1970s, a decline occurred partly due to the increase in use of pesticides and partly due to the Cultural Revolution (1965-75) during which the method was discouraged. In the mid-1980s a resurgence began, sponsored by the government. By 1996, 1.2 million ha were under cultivation and were producing 377,000 MT of fish.

In Japan, rice-fish farming reached a peak production of 3,400 MT in 1943 due to war-time subsidies but the practice declined swiftly after the war and has never recovered. Today, the practice is seldom used.

In Korea, rice-fish methods have never been popular in part because the limited demand for freshwater fish has been supplied by inland water. The practice is almost non-existent today.

In Indonesia, rice-fish farming was has been practiced on a fairly wide scale for >100 years. The Dutch promoted the concept so that by 1950 some 50,000 ha were in rice-fish farming. The area in rice-fish farming increased to around 150,000 ha by 2000.

In Thailand, rice-fish farming is believed to have been practiced for >200 years. the method was promoted by the government and reached a peak in the late 1960s. In the 1970s, however, HYVs and pesticides were introduced and led to a collapse of rice-fish farming. In recent years a recovery has begin as the use of pesticides has declined.

In Malasia, rice-fish farming has been practiced since at least 1928. As in Thailand, the method declined with double-cropping and rice and use of pesticides.

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In Vietnam, a strong rice-fish farming exists and also involves several species in addition (and even instead of) rice. The practices decreased with the introduction of HYVs and pesticides.

In The Philippines, there is a long tradition of harvesting wild fish in rice fields but rice-fish farming, as we are using the term, was tried only briefly, and only because of government sponsorship. After this sponsorship ended in the mid-1980s, the practice largely died out, though a resurgence may have started in 1999.

In India, rice-fish farming is widespread with 2 million ha in production by the early 1990s, the largest known for any country. the practice is quite diverse involving many ecosystems and >40 species of fish and shrimp. It is reported that the production of tiger shrimps P. monodon) exceeds 2 MT/ha in some areas.

In Bangladesh, the rice-fish farming has existed for centuries and is widespread. It is promoted by the government and NGOs including CARE with an active research and extension program.

In Australia, the practice is apparently not widespread but is being investigated by a large commercial operation.

In Madagascar, a long rice-fish tradition exists. The government began promoting the practice in 1952 but success was limited, in part due to lack of fingerlings, and by the late 1980s it was concluded that practice could only continue with subsidies. At that time, production was only 80 kg/ha indicating poor conditions, methods, or both.

In Malawi, rice-fish farming is “just beginning”.

In Zambia, rice-fish trials were reported by Coche in 1967 but the method did not become established. FAO promoted the concept starting in the early 1990s but economic analyses later showed that the method was not financially viable.

In Senegal, a small rice-fish farming has developed apparently stimulated by encroachment of seawater. To prevent this, farmer built fish ponds. I am not clear on whether this led to concurrent rice and fish methods. In any case, the activity appears to be minor.

Several other Africa countries (Zaire, Zimbabwe, Ivory Coast, Gabon, Liberia, Mali, and Benin) are reported to have conducted trials with rice-fish farming but little is known of the efforts and they certainly did not lead to wide use of the rice-fish method. Trials in West Africa were reviewed by Moehl et al. (2001) and are discussed separately below.

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In Egypt, which is the biggest rice producer in either the Middle East or Africa, rice-fish farming increased through the 1980s reaching a peak of 225,000 ha but then declining in response to HYVs, short seasons, and pesticides. Production began to rebound later in the 1990s and by 2000 was becoming extensive again.

In Iran, rice-fish farming apparently began only in the late 1990s but showed good results. Production on 18 farms was 1.5 MT of fish and 7 MT of rice. Many other farms have adopted a rotational system.

In Italy, by far the most important rice-growing country in Europe, rice-fish farming was introduced at the end of the 19th century and expanded during the next 40 years. With the introduction of HYVs, the practice gradually declined and was unimportant by 1967. Renewed interest exists, especially at the University of Bologna.

In Hungary, 45,000 ha of rice were once cultivated and rice-fish methods were important, in part due to the lack of marine fish, but the rice has large disappeared.

In the countries of the former Soviet Union information is sparse but it appears that rice-fish farming may have been present and even widespread in some areas.

In the neoptropics, rice is cultivated in 9 countries in South America and 8 in the Caribbean but it appears that rice-fish methods are not widespread. Efforts were made to develop and promote the method as early as the 1940s but have not yet been successful. Some progress has been made in two areas in Brazil.

In the United States, rice-fish methods were promoted in mid-1900s but did not catch on. At present crawfish are farmed in many rice fields in the SE.

In summary, rice-fish methods have been tried in virtually all rice-growing regions of the world. The current extent of the practice is as follows:

Extensive: China, India, Bangladesh, Indonesia, maybe EgyptLimited but perhaps expanding: Thailand, Italy, Iran, The Philippines, Vietnam?,

Australia, BrazilLittle or none: Japan, Korea, Malaysia, Madagascar, Zambia, Senegal, other African

countries, countries of the former Soviet Union, the Caribbean, South America except perhaps Brazil.

A few areas exist in which rice-fish farming was extensive but declined and did not recover after the introduction of HYVs (Thailand, Malasia, Vietnam, maybe Italy) but in China, India Bangladesh, and Indonesia, rice-fish farming has rebounded with the development of IPM methods so it does not seem reasonable to blame the lack of rice-fish farming, where it is not currently present, on the HYV methods. Furthermore, as

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Halwart and Gupta (2004, p. 65) acknowledge, “the adoption rate of rice-fish farming is very low.” For example, <4% of the rice fields in China use rice-fish methods and the proportion is ~1% or less in most if not all other areas. This reality suggests that considerable caution is needed in adopting fish-farming methods or assuming that they will increase the profits for rice paddies.

Rice-fish farming in Africa

Many authorities in Africa have advocated rice-fish farming, often referred to as Integrated Irrigation Aquaculture (IIA). The 21st FAO Regional Conference for Africa, held at Yaounde in 2000, acknowledged the importance of aquaculture, including rice-fish systems, and recommended that the FAO “assist governments in elaborating effective aquaculture policies and streamlining public sector support to foster increased aquaculture production” (Halwart and van Dam 2006). A conference sponsored by the FAO and WARDA in 2003 was devoted to this topic in West Africa (Halwart and van Dam 2006). FAO and WARDA have both recommended that IIA be expanded throughout West Africa. One outcome of the IIA Conference was a five-year project, Community-Based Fish Culture in Irrigation Systems and Seasonal Floodplains in Mali. Look this up. Other meetings mentioned in Halwart and van Dam have made similar statements.

Similarly, Miller (2006, p. 69) favored the development of irrigation aquaculture in West Africa:

Future efforts in aquaculture development should be oriented towards extensive fish production with low-cost, locally available inputs. High cost intensive aquaculture, such as cage fish farming and raceway farming, are inappropriate and uneconomical in conditions found in the Sahel and should be discouraged.

The new agricultural strategy for Sierra Leone is very optimistic about aquaculture (2010). For example, aquaculture is recommended as a priorit in all Districs (Sierra Leone 2010 p. 26).

Empirical results, however, have often been disappointing. According to Miller (2006)

Rice-fish farming has been attempted in [Senegal, Mali, Niger, Burkina Faso]. Most of these efforts unfortunately ended abruptly during floods with loss of fish and rice in some cases. Nevertheless, results from a few conclusive studies in Mali (Malengi-Ma, 1988; 1989) and Niger (Olivier et al., 1998) offer promise, as rice production was somewhat greater (up to 6-7 tonnes/ha/year) with the presence of fish which yielded between 130 and 190 kg/ha/year.

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According to Miller et al. (2006), “The Nigerian government invested in more than 50 fish farms, including a few with feed mills, but most of those lie abandoned today.” On the other hand, according to Bentz,

In 2001, a network of more than 420 fish farmers produced 170 tonnes of fish per year, from 160 ha of water. The project was assisted by two NGOs, APDRA-CI and APDRA-F (Association pisciculture et développement rural en Afrique tropicale humide–Côte d’Ivoire and France). The project was based on an extensive technology with fish yields between 0.5 and 2 tonnes/ha/yr, combined with extension and training through farmer field schools and participatory research and monitoring.

Rasowo and Auma (2006) stocked 6000 fingerlings/ha and left them in the rice paddies for 77 days during which their weights doubled. The fish harvest, however, were too small to be attractive to local buyers, and net profits from rice only and rice-fish paddies were nearly identical.

Conclusion

Aquaculture has an odd history. It appears to confer major economic and heath benefits. Yet despite having been tried in dozens of countries, it is now a major enterprise in only a few countries and even there it usually occurs on <2% of the land in rice production. Finally, in Africa, where it has been tried, it seems not have worked very well, and yet it is now being endorsed strongly by professional groups and the government. In conclusion, it seems likely that we can derive substantial economic and health benefits from rice-fish farming but we must proceed carefully to avoid the failures that have occurred so widely across Africa and throughout the world.

General approach

This section identifies the general approaches we would consider. Subsequent sections generally do not discuss other approaches. As noted above, we are not considering rotational systems because they would require producing water during the dry season which at present we do not know how to do.

Maturation time

A major constraint in our system is the rapid development time of the rice. Fish damage seedlings younger than about 30 days (Halwart and Gupta 2004, p. 40). With 90-day rice, we would probably remove the water, so fields can dry before harvest, by about day 75. Thus, the fish would only be in our paddies for about 45 days. This is far too little time for them to develop so we must either move them to other paddies or to ponds to complete their development. It might be possible to hold fish in refugia until the second rice crop was started (though Halwart and Gupta 2004, p. 23, say these periods should be

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kept short), or to transfer them to an adjacent paddy that had not yet matured (though large fish may damage rice plants Halwart and Gupta 2004, p. 18). . Whatever strategy we follow, it will have to accommodate the short period during which the paddies are flooded. A report by Halwart and Gupta (2004, p. 24) that in some areas, small fish are preferred to larger ones warrants investigation.

(Halwart and Gupta 2004, p. 40) say that fish are not usually released until 10-14 days after transplanting – and application of fertilizers – which would make the rice plants roughly 30 days old depending on transplanting age.

Polyculture

Many rice-fish systems include >1 species other than rice. Objectives may include higher fish yield, higher rice yield, or better control of disease. Halwart and Gupta (2004, p. 34) state that polyculture (multiple fish and perhaps other animals) tends to result in higher yields but counter examples exist. They also (p. 29) describe a case in which stocking common carp and grass carp resulted in better control (than stocking either alone) of insects, snails, and weeds due to the different feeding habitats of the two species.

An elaborate example of polyculture is described below: (source for the following?)

By utilizing the dikes of the rice fields to cultivate dryland crops the field can be described as a multi-level system. One such system is the surjan system (Figure 7) found in coastal areas with poor drainage in West Java, Indonesia. The dikes are raised to function as beds for dryland crops. The trenches, the rice area and the dikes form three levels for the fi sh, rice and dryland crops (Koesoemadinata and Costa-Pierce 1992). Xu (1995a) described a development resulting in a seven-layer rice-fish production system practiced in Chongqing City, China. The seven “layers” were: sugarcane on the ridges, rice in the fields, wild rice between the rows of rice, water chestnuts or water hyacinth on the water surface, silver carp in the upper layer of the water column, grass carp in the middle layer, and common carpor crucian carp at the bottom. In order to utilize rice fields comprehensively for better economic, ecological and social benefits, many experiments on multi level systems have been set up such as rice-crab-shrimp-fish in Jiangsu province, rice-fish-mushroom in Helongjiang Province, rice-fish-animal husbandry-melon-fruit-vegetables in Guizhou Province, and rice-lotus-button crab in Beijing (Li Kangmin, pers. comm.).

Accommodating the needs of >1 species, in addition to rice, presumably complicates designing an appropriate strategy, and this may be especially difficult for us with such a short flooding period. Nonetheless, it seems best to evaluate polyculture rather than excluding it at this time.

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Halwart and Gupta (2004) provide a thorough review of strategies that have been followed but conclude (p. 34-35) that local trials are needed to identify the optimal species, stocking rates, and feeding strategy.

Design and construction

See VHTR xx for discussion of basic rice paddy construction. In rice-fish systems the water is usually deeper (up to 25 cm vs 10-20 in rice only systems). As a result dikes must be taller and wider. Deep water “refugia” are also needed to provide cooler water for the fish and to aid in controlling their movements (e.g., for capture or when the rest of the paddy is drained). Drains must also be modified both because the dikes are larger and to control movements of the fish.

Refugia and dikes

Descriptive terms for refugia include trenches, ponds, and pits (or sumps), and the refugia may be within or adjacent to the paddy. None of these terms are rigorously defined.

Configuration and area covered

In most pictures I have seen, the trench runs along one to three sides of the paddy. In large paddies, a trench may also run through the middle. In “ridge and trench” systems (Fig. 6) narrow, shallow trenches alternate with ridges on which he rice are planted.

Fig. 6. Ridge and trench system in China (Li 1992 cited in Halwart and Gupta 2004, p. 15).

A shallow trench may also extend into the center of the paddy to help fish find the deeper trench (left).

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Coverage by the trenches seems to vary widely. Halwart and Gupta 2004, p. 16) describe systems in Asia in which deep water covered 28%, 33%, and 40% of the total area. They also say that in ridge and trench systems ridge width varies from 60-100 cm and ditch width varies from 35-50 cm. This suggests that ditches cover about 35% of the total area. In other reports, however, refugia are smaller. Pictures in FAO (2001) show trenches covering about 20% of the paddy, Rasowo and Auma (2006) reported that their trenches covered 10% of the paddies, and Halwart and Gupta (2004, p. 13) describe a system in the Philippines where coverage was as low as 5%. Since increasing the size of refugia reduces area devoted to growing rice, better information is needed on how extensive the refugia should be.

Dimensions

In rice-fish paddies, the dikes usually rise 40-50 cm above the paddy floor and are 40-50 cm wide (FAO 2001, Halmart and Gupta 2004, p. 12). The water is usually no more than 20 cm deep so the dike rises 20-30 cm above the water level which is sufficient to prevent fish from jumping the dike.

Trenches usually extend 50 cm below field level. With those depths, water remains cool enough for the fish, at least in the refuges, even if the paddy temperature reaches 40 C (Halwart and Gupta 2004, p. 23). FAO (2001) recommends that trenches be “much deeper” if holding the fish year-round is desired. The steepness of the sides varies with soil. They can be almost vertical in clay soil but must be much more gradual in sandy soil to prevent erosion.

In an intensive program, with a stocking rate of 6000 fry/ha, Rasowo and Auma (2006) used trenches 0.5-1.0 m deep that appeared to be 2-3 m wide in photographs. Their dikes were similar to the description above.

Construction details

FAO (2001) provides the diagram and the following notes.

A. Existing rice fieldB. Small dike (optional); useful to keep fish in the trench out of the rice field if desired

C. Slope of trend depends on soil type; more gradual in sandy soilsD. Water level in trenchE. “Lip” between trend and dike, keeps soil from dike out of trench.F. Side of dike; slope depends on nature of soil (gentle in sand); with top soil and grass, erosion is reduced

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G. Maximum flood level; point G is most important; the dikes should be high enough so they cannot be submerged by floodwaterH. Plants/trees gown on top of dike

Dikes should be compacted during construction if possible and the height should allow for compaction and some erosion. Top soil should be placed as shown in the drawing (note soil at bottom of trench). Some sites have an impermeable layer, such as organic soil, on top of a permeable layer, such as sand. Digging the trench may expose the permeable layer and lead to substantial water

loss if it the trend is not lined with impermeable soil.

Drains

Rice paddies often do not have drains or gates in the dike. Farmers simply remove a section of the dike, let water in or out, and then replace the soil. In rice-fish systems, this is unsatisfactory because farmers want to control whether the fish enter or leave. Furthermore, dikes are enough larger that removing and then replacing soil may be less feasible. Screens, and gates to which they can be attached, are therefore needed. With very small fields (0.1 ha), drains may be made of pipe, bamboo, or hollow logs, and a wire screen may be placed over the opening (left). Placing gravel under the drain may help avoid erosion. With paddies of the size we envisage (4 ha), more care is needed to avoid erosion and the screen must be larger and studier.

We have not found any advice on how large drains should be but it should be easy to calculate drainage times with different sized-opening using Bernoulli’s equation. I have not seen any discussion of variable gates so that water level could be adjusted but this seems desirable.

Other information

From Prein and Dey (2006):

A variety of studies show that reservoirs and canals of irrigation systems continue to yield substantial fish harvests, which are important sources of protein and livelihoods for the poor and landless households. Yet the current use of irrigation systems and floodplains for fish production falls far short of potential. ... In Cambodian floodplains, the value of fish caught through trap ponds within rice fields reaches 37

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to 42 percent of that of rice production (Gregory and Guttman, 1996; Guttman, 1999).

Paddy management

Water management

It is widely acknowledged that water management is a critical issue in rice-fish systems (Gowing 2003, Halwart and Gupta 2004, Sanni et al. 2006). From a fish production perspective, water should be kept as deep as the rice will tolerate, usually 15-20 cm. Rasowo and Auma (2006) maintained water height at 25 cm in the rice-fish paddies (and 20 cm in rice only paddies).

Water levels should be checked daily so that problems can be corrected immediately (FAO 2001).

Brugere (2006) discusses salinization resulting from aquaculture but it is unclear to me whether this is a problem in rainfed systems.

Brugere (2006) comments that wastewater form aquaculture can be used to “fertigate” fields, especially in arid areas with poor soil.

Azolla and other cover crops

Sanni et al. (2006, p. 76) state “the aquatic fern Azolla can be found nearly everywhere, but it is not formally farmed and farmers often ignore its properties”. According to Wikipedia

The nitrogen-fixing capability of Azolla has led to it being widely used as a biofertiliser, especially in parts of southeast Asia. Indeed, the plant has been used to bolster agricultural productivity in China for over a thousand years. When rice paddies are flooded in the spring, they can be inoculated with Azolla, which then quickly multiplies to cover the water, suppressing weeds. The rotting plant material releases nitrogen to the rice plants, providing up to nine tonnes of protein per hectare per year.

While growing Azolla in the paddies often seems to improve both rice and fish yield, this is not always the case (Halwart and Gupta 2004, p. 32). Wang et al. (1995, cited in Halwart and Gupta 2006 p. 32) reported a study of rice and catfish in which yield was

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highest without Azolla. In most studies I have seen, however, yields of fish seem highest when Azolla is present.

FAO (2001) mentions several other plants that may be used in a similar way including duckweed (Lemma), Wolffia, pak boong or kangkong (Ipomea aquatica) and water mimosa. Some fish do not eat all of these (though silver barb does). FAO (2001, p. 115) also notes that continuous cover by aquatic plants prevents poaching.

Stocking rates and species composition

Most stocking rates reported by Halwart and Gupta (2004, p. 29) were about 3000 fish/ha. FAO (2007) recommends 3000/ha and says only rarely should the rate be as high as 6000. They say that common carp, silver barb, and tilapia in a ratio of 2:2:1 works well in Thailand.

Fingerlings of some species damage young seedlings and thus must not be stocked too early Halwart and Gupta (2004, p. 18).

Rasowo and Auma (2006) stocked mixed sex tilapia weighing ~ 20 g at a rat of 6000 fish/ha 14 days after transplanting. The rice seedlings were 30 days old when transplanted.

Fertilizer, feeding, and maintenance

The distinction between fertilizer and feeds for fish is not clear (e.g., manure can be used for both). We refer to both as nutrients. The FAO (2001) says that (contrary to earlier literature) neither fertilizer nor feeding are needed at stocking levels below 3000 fish/ha. At higher stocking feeding may be necessary. The best approach is to give small amounts a few times a day and adjust the rate by checking to see how long occurs before it is consumed. Feed should be distributed across the paddy, not just placed in the trenches, so that fish will penetrate throughout the paddy (Halwart and Gupta 2001). The problem with adding large amounts of feed is that the high rate of decomposition may deplete the oxygen level.

Manure, either dry or moist, is one of the best additives. FAO (2001) says that up to 300 kg/ha can usually be added per week though caution may be needed if the water is stagnant. Rice bran is widely used but FAO (2001) questions the need and recommends against this unless the bran is free and readily available. Nearly any vegetation may be useful, however feeds should be matched to the species (Halwart and Gupta 2004, p. 30).

Rasowo and Auma (2006), who stocked 2-gm Nile tilapia at a rate of 6000 fish/ha, added rice bran at a rate of 2% of the total body weight of the fish per day. Diana et al. (1996

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cited in Halwart and Gupta 2004, p. 30) reported that starting feeding “late” did not increase harvest.

Detection and correction of problems

Oxygen depletion is a potential problem any time stocking rates are high or nutrients are added (because the nutrients stimulate the benthic community which may then consume enough oxygen to affect the fish). The most reliable way to detect oxygen depletion is through direct measurement of dissolved oxygen which is readily done using a variety of instruments. Other signs of oxygen depletion include fish gaping at the surface, air bubbles in the water, brownish or grayish water, and odors. In response, stop adding nutrients, replace the water, aerate it if possible.

If the pH falls below 4, fish kills are likely. Add lime to raise the pH.

Hydrogen sulphide is a poisonous gas emitted from decaying and decomposing organic matter. Its presence is indicated by the rotten egg smell and dead fish. To remove the gas, agitate the water, add freshwater, stop adding nutrients, as a last resort, drain the pond and let it dry for 1-2 weeks.

Cloudy water and fish that appear hungry indicate over-stocking. Remove fish and/or add fertilizer of feed.

High manure can lead to fish with poor taste. To avoid this, stop delivery of manure at least 2 days before harvest. Harvest fish without causing high turbidity which will contribute to the poor taste. Transfer the fish to a tank with running water for at least 4-6 hours and preferably several days. Sell fish live, or fresh.

Case study

Rasowo and Auma (2006) monitored dissolved oxygen, pH, temperature, alkalinity, orthophosphate, and nitrate-N each week at noon during a study in Kenya. While some of these would probably be difficult for us to monitor, we could easily monitor temperature, pH, and dissolved oxygen.

Effects on fish of controlling pests of rice

Manual weeding increases turbidity but Halwart and Gupta (2004, p. 40) say the frequency is generally low enough that fish are not usually significantly affected. Herbicides are not considered a serious threat to fish (FAO 2001, p. 109; Halwart and Gupta 2000, p. 41), in part because they are usually applied before, or soon after,

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transplanting whereas the fist are not released until 10-14 later. Halwart and Gupta (2000, p. 41) note that herbicides with low toxicity to fish can usually be found (Table 3). For example, Xiao (1992) listed nine herbicides being used in rice-fish farmings in Asia. Very high tolerances by C. carpio, M. rosenbergii, and a freshwater clam, Corbicula manilensis to 2,4-D or MCPA (Chlorophenoxyacetic acids) were reported by Cagauan and ARce (1992) an Xiao (1992). Furtermore, seeding ponds with Azolla, which quickly shades the ponds prevent weed growth, seems high desirable. Thus, adverse effects on fish of herbicides seem unlikely.

Insecticides may be much more harmful to fish (FAO 2001). According the Halwart and Gupta (2004, p 43), “no systematic evaluation” of the effects of insecticides on fish has been conducted. They summarize data from studies in 1992 (Table 3), but it is hard for me to believe there isn’t more recent and comprehensive information available.

Table 3. Toxicities of common insecticides and herbicides to three fish expressed as 48- and 96-hour LC50. et = extremely toxic; ht = highly tocix, mt = moderately toxic. Data from Cagauan and Arce 1992 as reported in Halwart and Gupta 2004, p. 45).

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FAO (2001, p. 109) recommends a number of steps to reduce adverse effects of pesticides on fish:

+ select pesticides with low toxicity to fish+ apply powder pesticides in the morning when dew is still on the leaves but apply

liquid in the afternoon when the leaves are dry+ minimize the amount of pesticide that gets into water+ apply at the optimal time+ move fish to refugia prior to application and hold them there until the pesticide

loses its toxicity+ increase water depth as much as possible to dilute the pesticide+ prior to spraying open the inlet and outlet so that water flows through the paddy and

carries deposited spray away

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The insecticide, Furadan (Curaterr), is incorporated into the soil at the final harrowing and provides protection for 50-55 days. After this time, rice leaves are thick and dense and catch most of aerially applied pesticide.

Harvest

Methods and timing

(timing and methods of harvest)

Rasowo and Auma (2006) added 20-gram O. niloticus to rice-fish paddies and harvest them 77 days later.

In the trials by Dey and Prein (2004) in Bangladesh, fish were in the water for 150-210 days.

Expected production

Halwart and Gupta (2004, p. 30) reported that stocking 3000 fingerlings/ha yielded 118 kg/ha at harvest and 6000 fingerlings/ha yielded 571 kg/ha at harvest. Li and Pan (1992, cited in Halwart and Gupta 2004, p. 30) estimated that with optimal management, including multiple fish species and addition of detritus and bacteria, a paddy can support about 500 kg/ha. With multiple harvests/year, the annual production could exceed 1 MT/ha.

Halwart and Gupta (2004 p. 33) provide a table of harvest under different systems and in different countries. Values varied widely from <100 to >3000 kg/ha. Most of the values >1000 were in brackish or deep (>0.5 m) water or were for annual production. Most other values for concurrent systems were <500 kg/ha. Halwart and Gupta (2004, p. 32) summarize their data as follows: Without feeding the production per crop can range from 100 to 750 kg/ha-yr (Zhang 1995), with feeding the result might be 1,812 kg/ha-yr. Thus, production during half a year of 1,000 kg/ha is possible but will probably be quite difficult to achieve.

Gowing (2006) says production of 1.5-2.0 kg/ha-yr is feasible even in “low-cost, semi-intensive systems” however they do not provide much justification for this claim which seems high in light of the reuslts presented above.

Prein and Dey (2006) report that “community-based fish culture in rice fields can increase fish production by about 600 kg/ha/year in shallow flooded areas and up to 1.5 tonnes/ha/year in deep-flooded areas, without reduction in rice yield and wild fish catch.”

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Case histories

Rasowo and Auma (2006) stocked 20-g Nile tilapia at a rate of 6000 fish/ha. Their trenches were 0.5-1 m deep, 2-3 m wide, and covered 10% of their paddies. They mention that fertilizer (urea and NPK) were applied to the rice but do not provide details. They monitored dissolved oxygen, pH, temperature, alkalinity, orthophosphate, and nitrate-N each week at noon. Water temperatures remained with the optimum range (29-32 C) for O. niloticus. DO values were higher in fields than trenches but declined, probably due to shading as the rice developed (rice cover is reported to increase from 50% at 15 days to 85% at 30 days to 95% a 60 days, Halwart et al. 1996). DO levels in refugia were lower than 5 mg/l, a level below which fish growth is retarded (Boyd 1982), in the mornings but increase during the day. pH was slightly low but within the range considered acceptable for fish growth (Boyd 1982). They seem to recommend liming – a an uncommon practice in Kenya at present. The nitrate-N levels were “fairly high” but “should have been higher” due to the fertilizers applied. Fish were kept in the paddies for 77 days. During this time, they doubled their weight to 37 g). Local residents were used to 150-g fish (from Lake Victoria) so price per kg was probably lower than it would have been with larger fish. Harvest was a low 132 kg/ha but recovery rate was only 43% probably due to fish escaping or being poached. Yields of rice were slightly, but not significantly, different in the rice and rice-fish paddies. In the rice-fish paddies the average yield was 4.7 MT/ha whereas in the rice-only paddy it was 5.75 MT/ha. The difference was not significant. Most yields were above 5 MT/ha and one was nearly 8 MT/ha. Net returns were nearly identical at $992 (rice only) and $1000 (rice-fish). The major fish costs were the fingerlings (64%) and the rice bran.

Other information

There is much discussion of effects of wild predators. It seems that keeping them out, as long as we are using rainwater, should be possible (or maybe larger conspecifics count as predators).

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Post-harvest processing

Brugere (2006) comments that most fish in West Africa are sold fresh but also that health issue can arise such as invasion of fish by dermestid beetles.

Miller (2006, p. 69-70) states

Post-harvest losses should be reduced. Fish are smoked in all four countries under study and loss due to spoilage and infestation with insects may be as high as 50%. This can be greatly improved through training in improved fish smoking techniques, to achieve a reduction in the use of fire wood, reduction in fire outbreaks and a greatly improved product with a longer shelf life. Women need training in this technology and access to rural credit and savings programmes.

Marketing

Economic analysis

Halwart and Gupta (2004, p. 49) tabulated costs, income, and net returns in rice production, with and without fish, in all of the locations they could find (Table 2). Data come from before 1990. Returns from the rice-fish systems were higher in all cases

Table 2. Comparison of costs, income and return to labor with and without fish (Halwart and Gupta 2004, p. 49). All figures are in USD/ha in 1987.

Country

Rice onlyRice onlyRice only Rice-fishRice-fishRice-fishRice-fishRice-fishRice-fish Differ-ence

(fish-no fish)

Ratio (fish/

no fish)Country

In-come

Ex-penses

Net income

IncomeIncome ExpensesExpensesExpensesNet

income

Differ-ence

(fish-no fish)

Ratio (fish/

no fish)Country

In-come

Ex-penses

Net income rice fish rice fish total

Net income

Differ-ence

(fish-no fish)

Ratio (fish/

no fish)

Bangladesh 690 326 364 749 195 302 72 374 570 206 1.57Bangladesh 444 137 307 464 183 121 31 152 495 188 1.61China 562 158 404 559 864 131 202 333 1090 686 2.70China 405 588 183 1.45Indonesia 1663 770 893 1518 490 621 122 743 1265 372 1.42Philippines 700 469 231 674 126 506 294 63 1.27Philippines 757 390 367 1098 607 322 242 564 1141 774 3.11Philippines 1579 1143 436 2077 1126 1860 1343 907 3.08Thailand 160 120 -40 0.75

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Vietnam 268 334 66 1.25Averages 914 485 384 1020 513 299 134 647 724 341 1.82 except in Thailand where individual costs and incomes are not available but the net income from both rice only and rice-fish systems was very low. The average difference in net incomes was $341, or about $700 in 2010 dollars. Net returns with fish were about twice the net return for rice only paddies. Since these data were collected in the 1980s, rice production and profits/ha have increased substantially whereas fish production/ha has increased more slowly. The ratio of net incomes thus may have changed substantially. The difference in net incomes, however, should be much more similar. It would be higher than in the 1980s because fish lead to an increase in rice (of about 10% based both on data summarized above and on income derived from rice in Table 3). Thus, a net increase in profits/ha of about $1000/ha seems plausible, and it might be higher using aquaculture methods not available in the 1980s. Projected profits from rice in our area are now about $4000 (see VHTR 19) so this would represent a 25% increase in profits. this analysis thus suggests a substantial increase in profits as a result of adding fish to our rice paddies.

All the studies above are from Asia. Results from Africa are sparse and mixed.

Ofori et al. (2005) compared rice and rice-fish systems in Ghana. The fish were raised for 100 and 120 days. Net returns (including sale of rice) were $1000/1200/ha and were 5-11% higher on the rice-fish paddies.

Halwart and van Dam (2006, p. xi) report that inland fisheries in West Africa are generally declining, suggesting that the prices for fish are unlikely to fall.

Ahmed et al. (2010) assessed economic returns from raising prawns in rice fields in Bangladesh. The average yields (MT/ha) were prawns, 467; fish, 986; and rice, 2257. All farmers made a profit but the returns/ha were related to area held by the farmer: large, $2426, intermediate $1798, and small $1420.

PART FOUR: POND AQUACULTURE

(to be completed)

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