Fish Pond ConstructionBooklet No. 520

Fisheries and Aquaculture: FACS - 6ContentsPreface I. Introduction II. Classification of Fish Ponds III. Types of Fish Ponds IV. Key Points in Pond Construction V. Survey of the Location VI. Layout of Fish Ponds VII, Construction Details VIII. Post Construction Operations IX. Conclusion

Preface

Fish pond is like a vessel that should hold sufficient water throughout the year for a desired number of fish or fishes to live and grow comfortably. The main point in the construction of a fish pond is to make sure that it remains intact for a long period of time so that it becomes a permanent asset that will give regular income to the owner of the pond. Very often the construction of the pond is done very carelessly or inadequately that within one year or two the pond becomes unfit for fish rearing. Our experience shows that people are ignorant about the various aspects of the construction of a fish pond. I am quite aware of the need for a number of diagrams to highlight the construction details of the fish pond. However due to very high cost they cannot be included. Besides, engineering diagrams cannot be understood by ordinary people without the help of some technically qualified people.

Dr. K T. Chandy, Agricultural Environmental Education

I. lntroduction

The construction of fish pond involves the knowledge of variety of things like the type of soil, the angle of retention of a particular type of soil, soil management for construction, the interaction relationship between water and soil, the behavaior of soils under the permanently wet and submerged conditions etc. Only then one can construct a proper fish pond which can last many years and in which fish rearing can be practiced regularly.

Fish rearing involves supervision and regulation of reproduction, feeding, disease control, control of the size of the fish and the stocking and maintenance of the ponds. This means we should have the full control of the fish rearing situation in the constructed pond so that always an optimum range of environmental condition is made available to an optimum number of fish per unit area of the pond.

The construction of the pond should be such that there should be least amount of seepage or leakage loss of water, safe from siltation, side collapse and filling of the pond, safe from other predatory terrestrial and aquatic animals, tree from the possibility of flooding or overflowing of water or drying or serious reduction of water.

The pond also to be constructed in such a way that feeding and caring of the fish, disease control, supervision, control of inlet and outlet of water from the pond and finally the netting and harvesting of fish becomes easy.

Fish pond can be constructed at any place where sufficient amount of water is available. If it is fresh water then fresh water fishes can be reared, if brackish water then brackish water fishes can be reared; if sewage and marshy type of water then air breathing type of fishes can be reared. We can find all kinds of fishes growing in all types of water provided the pond is capable of maintaining the water level and quality within certain range of the optimum level.

In this booklet some of the obvious aspects of the construction of the fish ponds are explained.

II. Classification of Fish Ponds

Fish pond can be classified according to water supply, type of rearing and types of fishes, etc. This section of the booklet is to provide the reader some general understanding of the possible classifications of the fish ponds.

Water, being the primary medium for the fish growth and development, the first classification of the fish pond is based on the source of water.

1. Spring water pondThe source of water is a spring at the bottom or sides of the pond or from a spring

outside the pond. Normally such springs are excellent sources of fresh water and well suited for rearing fresh water fishes.

2. Rain water pondAs it is clear from the term, the source of water is rain water in general. However the rain

water may be collection of roof water, run off water from a catchment area.

3. Ponds supplied by river or streamSometimes ponds are constructed close to the river or stream and water is allowed to

flow into it through controlled inlets.

4. Rice field pondsOne of the corners or of one side the rice fields are dug into very small ponds or ditches

of suitable size and shape to rear fish as an additional source of nutrition and income, Here the source of water to the pond is water from the rice fields. At times one of the whole rice plots are converted into fish-ponds besides the small ponds in each rice field. During the flooded rice growing season, the fishes swim and feed around the whole field. In order to avoid the fish going out wire meshes are placed at the inlets as well as outlets and the bunds around are made strong and high. At the harvest of rice the field is dried. At that time the fish accumulate into the ditch where they can be reared for some more time till they are harvested.

5. Sewage water pondsOften treated or untreated sewage water can be a good substratum for fish rearing. The

domestic sewage water is collected into a pond and fishes can be reared.

6. Marshy area ponds

Often marshy or low lying areas are found in many places. Such areas can be properly modified into ponds suit- able to grow fishes.

7. Brackish water pondsBrackish water is found near sea shores or even in certain island areas and the ponds

filled with such water obviously will be brackish water pond.

8. Under ground water pondIn these ponds water from the under ground water sources is pumped into them

periodically to supply the required amount of water.

III. Types of Fish Ponds

Based on the usages the fish ponds are categorised into breeding ponds, spawning ponds, hatchery ponds, nursery ponds, rearing ponds and stocking ponds or storage ponds. They are defined and described here.

1. Breeding pondThis is a small pond in which selected female and male are maintained and the

preparations which may be artificial or natural for spawning is done. Details on breeding techniques are separately given in another booklet.

2. Spawning pondSpawning pond is a small pond in which selected male and female fishes are allowed to

discharge their ova and sperms into the water and which adhere to some vegetation or fibrous material provided. The ova mass discharged become jelly like in contact with water and stick to the vegetation at some point and the rest float in water. The sperms (milt) discharged by the male by the side of the ova mass, swim around and fertilize each ovum.

3. Hatchery pondsThe ponds in which hatching is done are called hatchery ponds. In many cases to

improve the efficiency of hatching separate ponds are maintained. The spawns from all the spawning ponds are collected and placed in hatchery ponds and provide optimum conditions for hatched larvae.

4. Nursery pondsAfter three to four days after hatching the frys start eating. From this stage till they are

transferred to the stocking pond the frys remain in the nursery ponds. Each batch of frys can have separate nursery ponds, for trys 4-15 days old, 15- 30 days, 30-90 days and 90-180 days depending on the production intensity one is following. Sometimes several nursery ponds are maintained at the same time nursing several batches of frys.

5. Rearing pondsLiterally rearing ponds are those in which the frys are reared as an intermediary between

nursery and stocking pond. The nursery stage of 90-180 days also can be considered as rearing stage. The fishes in the rearing ponds are at the fastest growing stage which will be continued in the stocking ponds.

6. Stocking or storage pondsStocking pond is the last stage pond in which fishes are grown till they are at market

size. Comparatively this is the biggest of the ponds.

For ordinary fish farmer all these types of ponds are not available nor needed. Small enclosed arrangements within the stocking pond itself can provide facilities for breeding, spawning, hatching, etc. The easiest arrangement is to fix proper net in the form of an inverted box in the pond. So water level in the net is same as that in the pond. By increasing the size of netted area one can get the advantages of breeding, spawning, hatching and rearing operations. Finally the net is removed and the fishes are allowed to spread themselves into the stocking pond.

Different ponds are maintained for different purposes only when the standards of breeding, hatching, rearing, disease control and management practices are very high.

Some other types of ponds are also possible as mentioned briefly here. Based on the shape of the ponds we have square, rectangular, triangular, trapezoidal, irregular, circular ponds or ponds constructed in contours.

Based on the depth of the ponds we may have deep, shallow or medium deep ponds. Based on the type of fishes grown we can have carnivorous fish ponds or herbivorous fish ponds. Based on the climatic conditions we have cold water ponds, ponds with water of normal temperature or warn- water ponds as in the tropics.

Again the ponds may be single or in groups, they may be linked or separate, they may be constructed parallel to each other or some other ways.

Based on the type of fish we can have ponds for separate fishes like rohu pond, calla pond, carp pond, prawn pond etc.

Based on the size of the ponds we have big ponds of one acre and above or small ponds less than one acre up to a hundredth of an acre or even a small tank of few square feet.

Based on the material of construction we can have mud ponds, concrete walled ponds, stone or brick walled ponds, plastic layered ponds, mud walled ponds etc. Based on whether the water is running or stagnant we can have stagnant water pond or running water pond. Based on the trapping in of the water we can have barrage ponds, diversion ponds or pumped in-water pond.

IV. Key points in Pond Construction

Certain points should be kept in mind while constructing the fish ponds. Enumeration of these points together will help the fish farmer to plan the construction of the pond in advance and to avoid future problems. It also will help him to have more accurate financial estimates and plan for his fishrearing enterprise. The key points are the following.

A. The sizeThere should be proper size and shape for ponds used for various poses like breeding,

spawning, hatching, nursery, rearing and stocking. Often ordinary people have only one pond in wl1ich they rear fish from the nursery stage to the selling stage. Under such conditions they should have at least a pond size of 70 ft long, 35 ft width and 4-5 ft water depth. The ratio between the length and width of the pond should be maintained between 2:1 to 4:1 (the width should be less than half the length). This is to provide the fish long stretches of swimming and

feeding space and also for easy netting. Otherwise the optimum sizes of the ponds for various commercial purposes are the following. The size of various ponds are given in relation to pond of one hectare of stocking pond. Therefore according to the size of the stocking pond one can calculate the size of various ponds for breeding, spawning, hatching, nursery and rearing.

1. Stocking pond or growing pondStocking pond of standard size is 1.0 ha area and about 2.0 to 2.5 metre of water depth.

2. Rearing pondOn the basis of the dimensions of the stocking pond already given, rearing pond needs

0.1 ha area in size and 1.5 to 2.0 metre of water depth.

3. Nursery pondNursery pond requires an area of 0.06 ha and 1.0 to 1.5 metre of water depth.

4. Hatchery pondHatchery pond could be the same as the nursery pond in the case of small scale fish

farming, but in case one wishes to be a separate pond then he can have a small pond of convenient size about 0.03 ha area and 0.75 to 1.0 metre water depth.

5. Breeding pondBreeding ponds could be 0.02 ha area and 0.75 to 1.00 metre water depth. Breeding

pond could be same as the hatchery pond. But if one intends to have breeding of large number of the same type fish or different types of fishes at the commercial level then he should have several small ponds. He can also have small pre-fabricated concrete or plastic tanks for breeding different breeds of fish and to hatch them separately. Even small tubs of plastic and concrete can also be used for breeding different fishes.

The above mentioned various types of ponds are required for highly specialised breeding or large scale commercial level fingerling production and fish farming. For the ordinary farmers who may be having only a small general purpose pond, can use the same for various purposes by enclosing a small portion of the pond with the help of nets or using separate small concrete or plastic tanks or tubs.

The size is given in area and therefore the proportionate length and width of the ponds have to be calculated for each of the pond area given above. According to the land available, one can fix length or width and then the other can be calculated. Also one has to be proficient in the conversions of hectare into square metre or hectare into acre and to square ft. etc. (One hectare = 10,000 sq. metre, one ha = 2.5 acres, One acre = 43560 sq ft, one acre = 4000 sq metres).

The recommended and relative dimensions of the ponds used for various purposes are given for the benefit of the reader and pond fish grower, so that he knows what is the optimum relative size of the various types of ponds.

B. The sidesThe sides of the pond should be made really firm and non collapsible. This is done by

various ways like giving proper slope, compacting the soil, building or lining the sides with bricks or stones or concreting etc. A collapsed pond is like a broken vessel which cannot hold water in it.

C. Water retentionThe pond should retain sufficient water throughout/the rearing and growing season. In

other words it should be made leak proof. This can be made by compacting the soil, puddling the soil, adding more clay and other binding material to soil at the bottom and at the sides of the pond. The top soil layer (up to 6-9 inches depth) should be so compacted that practically no seepage loss is there, though compacting is a one time labourious process.

D. DrainageThere should be proper drainage facility. We should fix a proper outlet from the pond

through which we should be able to drain the pond fully or partially at any time without allowing the fish to come out.

E. InletThe inlet brings in water into the pond. This should be constructed in such a way that silt,

leaves or other plant parts should not come into the pond. The inlet should also control the quantity of water coming into the pond whether during flood, rain or dry season. In short, inlet controls the quality and quantity of water coming into the pond.

F. OutletThe outlet could be same as drainage or separate. In a running water pond a separate

and permanent outlet is fixed besides a drain. The outlet is fixed in such a way that the fishes from the pond should not escape. The water level in the pond is maintained and the quantity of water flow can be controlled.

G. BundsProper bunds of about 2-2.5 ft. height and of convenient width is needed all around each

pond. These bunds serve not only as boundaries but also as passages to move around and between ponds. The dimensions of the bunds such as length, width at the bottom and top, the height and thickness of the bunds should be even and uniform through out the bunds. Similarly the compactness of the bunds also should be uniform.

H. ApproachProper approaches to the pond site, to each pond and to the bottom of each pond is

necessary for easy movement of people and things in the fish pond area.

I. Siltation controlThere should be proper control of the silt possibly coming into the pond during the rainy

season. There should be properly constructed silt catching traps before the water enters the inlet.

J. Quality of waterThe quality of the water should be maintained suitable for the fish growth, especially the

amount of dissolved oxygen content. The water also should not be acidic or alkaline but neutral for all the fresh water fishes. But for the brackish water fishes one should ensure the brackish water. Sometimes the water may be acidic or alkaline at the source itself due to the type of soil and the rocks through which the water comes in. The water also should be clean and transparent to allow sunlight to reach the bottom of the pond.

K. Natural feed productionNatural feed consisting of aquatic flora and fauna are essential for healthy fish culture.

Hence in all the fish ponds special care should be provided to generate maximum natural feed.

L. Technical know-howIn actual situations of fish rearing what is mostly lacking is technical know-how. Proper

technical knowledge backed by sufficient theoretical understanding is the brain and back bone of fisheries. For long term fish culture, timely updating of the technical know-how is necessary for the success of the enterprises.

V. Survey of the Location The above mentioned points will be the main check points for surveying an area

proposed for the fish pond construction. Before constructing the pond obviously the spot selection is done mainly based on the water availability and easiness for construction and maintenance of the ponds. Other factors like transport, communication, availability of teed and other requirements marketing etc. are also taken into consideration. Once these factors are taken into consideration and a spot is selected for the construction of the pond, the type of soil, climate and topography are studied. The type of soil refers to whether it is clay, silt or sand or combinations of any of the two or three at varying proportions. One should also know whether the place has a tropical, temperate or cold climate and the topography whether it is leveled, undulated or sloping; if it is sloping what is the angle of slope. Along with this the water retention capacity, permeability, plasticity and chemical nature (acidic or alkaline) of the soil are estimated either scientifically or through the local peoples knowledge.

Ponds are best constructed on levelled land or in the valleys and lowest part of some catchment areas where the water table is high. Construction of pond is easier in the clay soil however if one has proper knowledge he can make a pond in any type of soil.

It is important to know the rain fall of the place and the seasonal and climatic variation of the place especially the relative humidity. Because based on the relative humidity the rate of evapo-transpiration varies. In very dry areas the water loss through the evapo-transpiration will be very high.

Depending on the type of fish rearing practice, the specific purpose whether it is for breeding, spawning or hatching and the size of the business are further points that could also be included. The results of the survey are tabulated and pre- served for future reference.

A summary of the points for survey are given here.

1. Is there adequate supply of water for fish pond'?2. Is the soil able to hold enough water in the pond'?3. Is the land suitable, and in good shape to have a fish pond?4. Who owns the land?5. Is the pond area close to home?6. Is there a market for the fish produced?7. Are there transport and communication facilities through out the year?8. Are there enough people to help to build and harvest the pond?9. Can the equipments and material for the pond construction be bought, borrowed or built?10. Can the fish be stored for few days if market is delayed? 11. Availability of fish feed: both natural and artificial?

12. Are the fertilizers available ?13. Do people'in the area like the fish? 14. Can the people of the area afford to buy the fish?15. What is the rainfall of the area, and what is the overflow frequency and duration'?16. What level of fish culture technology is available locally and how many families are is having it?17. What administrative and financial help can be obtained?18. How are the by-product of fish culture like the wastes of feed, fish and aquatic weeds going to be used?19. Is there possibility of at least primary processing and value addition to the product?20. What is the possibility of making the pond as a permanent asset to have regular income generation?

VI. Layout of Fish Ponds

Layout means the location and arrangement of ponds. Fish Pond layout is a branch of fishery engineering. The possible layout is to be studied, planned meticulously and preferably be made into a blue print.

The layout gives the full plan of the location of the ponds and mainly takes care of the placement of various ponds in relation to people, water flow and material movement in the pond area. Each layout will be different and specifically planned to adjust and accommodate the needs and the resources.

It is very difficult to lay down some general rules for layout planning. However the necessary dimensions of length, width and depth and the points to be kept in mind in constructing a pond (as given in section V) are to be considered while a layout plan is made.

Some of the key principles to be followed in the layout planning are mentioned here.

1. Ponds parellel to the common inlet channel: In this layout the width sides of all ponds will be parallel to the inlet channel. The same inlet channel is used to let in as well as let out water. This layout is used in places where rainfall is low and the ponds depend on artificially supplied water. In this layout system the outlet is not needed. However, water in the ponds will always be stagnant.2. Ponds having inlet and outlet channels parallel on both width-sides. In this system the inlet channel brings in water into each pond separately and also is drained out into outlet channel separately. This type of layout is used when one has a continuous flow of water.

Both the layout systems mentioned here can be modified into such a way that water entering the first pond after it is full, flow out into the second and then to the third and so on and so forth as people ordinarily do for paddy cultivation. This could be called "relay layout". Among farmers this is the most commonly followed system but it is the least preferred layout for commercial fisheries, because in such layout maximum disease incidence and other economic risks are inherent.

Pond width parallel to inlet channel, pond width parallel to inlet and outlet channel and the relay type of water flow ponds are regular shaped layouts, the rest may be called irregular types.

The irregular type of layout do not follow any fixed pattern. Ponds of various types and shapes are arranged in such a way that the fishery can be managed easily. The arrangement should be such that each pond receives water from the inlet channel separately and also drains out into outlet channel separately. In other words one should have full control of the quantity and quality of water flowing in and out of the pond.

If possible the length-sides of all the ponds should be fixed east-west to benefit maximum from the sun rays. Locate the watch and ward building in such a place that at least most of the ponds are in view of the manager, the watchman or workers.

In high rainfall areas and at the valley of mountains diversion channel should be constructed to ward off sudden onrush of rain water from the upper areas of fish pond lay-outs.

The layout also should consider the protection of pond area from wild animals, predators and thieves. This also include wild and unwanted fishes from outside. The layout should include facilities for feed storage and distribution, regular inspection and supervision for sample catching, for netting and harvesting for fish.

When there are several ponds in the same line and there are several lines of ponds, they can be arranged in series (one after another) in the same line and parallel between the lines. If there are number of ponds for each purpose such as breeding, spawning etc, then layout can be in blocks like nursery block and block for breeding, spawning, and hatching. We can also have blocks of ponds in such a way that each block is having all the ponds from breeding to stocking ponds. The exact layout pattern depends on the location, topography, climate, water source, intensity of production and the specialization of production whether for fry production or fish production.

VII. Construction Details

The construction details and the procedure of construction varies trom place to place and from purpose to purpose. It is also not really possible to anticipate and plan all the details of constructions. However certain amount of planning and procedures can be identified. They are as follows.

1. Prepare a master planWhether the pond is small or big, single or complex, single line or in blocks whether for

home use or for commercial purposes, a master plan should be prepared before one actually start digging the fish pond. Decide the length, width, depth at various comers and middle of each pond and the locations of the inlet and outlet estimate the volume of the soil to be excavated while digging the pond or making the dikes or bunds. Estimate also the slope of the sides depending on the type of soil.

2. Slope of the sidesDepending on the type of the soil, various possible tentative slopes can be given. For

very clayey soil we can give a slope of 1:1 to 1:1.5; for the sandy soils we should give a slope of 1:2.5 to 1:4; for the soils coming in between these two types and depending on the proportion of the clay or sand the slope is determined. More the sand lesser the slope. Such slopes are given when the sides are made of mud only. if the pond is deep there should be steps or platform all around the sides for every 4 to 4.5 ft continuous sloping distance.

If the sides are constructed with brick or stone walls, then the above mentioned slopes are not applicable. Needless to mention that it is always advantageous in the long run to

construct the sides with brick or stone fortified with cement. Because it will avoid the chances of the formation of horizontal holes and small caves which will lead to the collapse of the sides. Besides, vertical sides will increase the water volume of the pond. However while constructing the sides it is better to provide as many pockets of clay as possible so that sufficient flora and fauna can grow on these pockets to provide natural feed to the fishes. The clay pockets can be easily prepared by the arrangement of well baked clay bricks in a honey comb fashion on all the sides.

3. Inlet for waterThe inlet for the water to the pond should be constructed in such a way that water should

come into the pond without eroding the sides nor the bottom. If there is any possibility of the silt coming into the pond along with the water, then proper silt catching structures such as ditches, trenches, bunds or any other suitable structures should be provided. A properly constructed water inlet must fulfill the following conditions: (i) it must assure a regular and regulatable supply of water to the pond; (ii) it must prevent the escape of fish, (iii) it must keep out undesirable fish which might come in through the water fed into the pond. For this, a single or double screened case bitters can be installed at the inlet. The inlet could be a common one for a group of ponds or for individual ponds. The clogging of the screen by the debris etc. could be prevented by building a small check or weir and the debris collected should be cleaned off periodically.

4. By passAlong with the inlet there should be a by-pass to divert the excess water that could

possibly be coming into the pond during the rainy season. The depth and the size of the by-pass channel depends on the situation of the place and the position of the pond in relation to the incoming water and the slope of the area from which the water is coming. The by-pass can also be constructed with bricks or stone and cement which is ideal for long term commercial fish ponds.

5. Bottom of the pondThe bottom of the pond should be made firm and leak proof. This can be done by

repeated puddling of the bottom soil mixed with clay and allowing it to settle for a week and then again puddling it and allowing it to settle for a number of times till one find that water seepage is almost nill. Cementing or laying bricks or tiles etc. are other types of pond bottom treatment which of course will be very costly. It is better to make the bottom of the pond slightly sloping towards one side or to the drainage at the bottom of the pond.

6. Drainage or outletEvery pond should be fitted with a drainage by which we can drain out water whenever

we need. This can be done by fitting a big pipe from underneath the pond towards the lower area outside the pond. The outside end of the pipe can be fitted with a flexible pipe which can be fixed vertically up with its end rising high above the water level in the pond to preserve the water in the pond and put down on the ground to drain out the water from the pond. Only at the beginning of the outlet there should be proper screens and checks fixed so that the outlet is not blocked either by mud or by any other materials from the pond. This is also needed to prevent fish coming out. But this type of drain is possible only when at least one side of the pond is lower than the bottom of the pond.

The drainage structure can be of varying types and sizes as per availability of the designs such as sluices (an artificial channel for conducting water fitted with a gate at the upper end for regulating the flow) and monks (monk is a device resulting from the combination of sluice and

an underground drainage pipe). Siphoning is another easy method of draining the water from the pond.

7. Screens at the inlets and outletsOne of the difficulties that arises during the management of fish ponds is the frequent

clogging of inlets and outlets. Therefore both at the inlet and outlets suitable screens or filters or traps have to be fitted. There are several designs for this and it is better to consult an engineer for the suitable designs. To provide details of designs to fit screens, is beyond the scope of this booklet. For the inlet the easiest structure is to have a rectangular top-open box like tank fitted at the inlet. The first half of the tank receive incoming water. The second half of the tank is fitted with vertically sliding screens. These could be more than one screen in succession with sufficient space for collection of clogging materials which can be peri- odically removed. For the outlet the easiest way is to use siphoning into a lower area or a well from which water is pumped out. At the beginning of the outlet one or two screens could be fitted as is seen in the case of suction pipe of a pump set.

8. Bunds or dikes around the pondAll around the pond there should be a bund sufficiently broad enough to be used as path

to go around the pond for doing various kinds of pond management activities. The height of the bund should be about two feet above the water level. However too high or too low bunds should be avoided. If there are several ponds the bunds of all the ponds are linked together with connecting paths. This will enable easy movement of the people, implements, instruments and in some cases even vehicles. The bunds should be covered with grass to avoid soil erosion, breakage and collapse. Selected trees could be planted around the bunds to provide partial shading to the pond in areas where very high intensity of sun rays and summer is prevalent; however they should not be too many to breake the bunds by sending the roots or shading beyond 50 per cent of the area. Generally trees with tap root system should not be planted. If there is any problem of shading, prune sufficient number of selected branches to provide sun- light to the pond.

9. ApproachesThere should be at least one well constructed staircase leading to the bottom of the

pond in case of the small ponds. But in the case of bigger ponds several such stair cases are needed; at least at every corner. These are essential for the efficient execution of the various management operations such as feeding, cleaning, manuring etc. to be performed in fish farming.

10. Office facilityAs in any commercial activity in fish production also there are records and accounts to

be maintained and strict supervision and guarding of the ponds is ensured. The common records to be maintained are the following.i. Breeding records: which would show the date of breeding, the number and types of fish bred, ii. Spawning records: which would show whether the spawning has been successful and satisfactory or not;iii. Hatching record: which would show the date of hatching, the vigour of the fishlings hatched, whether hatching is satisfactory or not;iv. Nursery record: which will note the date of introduction of fishlings into the nursery pond, rate and the amount of feeding, the rate of growth in the nursery pond etc.;v. Stocking record: which will show the date of introduction of fingerlings into the stocking pond, feeding rate, growth rate etc.

vi. Records of daily operations, special operations, disease control measures etc. Harvesting records include date of harvesting, total yield, yield per unit area etc.

Office is also necessary to receive visitors and customers coming to the pond site. In commercial farms communication facilities like phones and fax may be also fitted. There should be electricity or other sources of power. Even for a home level fish pond a small office with electricity and other essential facilities is useful.

11. Storage facilityWhether the fish pond is big or small, for commercial or home level consumption,

adequate storage facilities at the site are necessary. Facilities are required for storing feed, implements and instruments, nets, baskets, weighing balance etc. Some times we may have to store harvested fish for few hours at the farm before that can be lifted to the market.

12. TransportA commercial fish farmer should ensure that there is link road from the farm to the public

road so that things required ; for the fish farm as well as things from the farm can be transported easily up and down.

VIII. Post Construction Operations

After the physical construction of fish pond, it is also important to test the ponds for their utility. Thus the utility test also is part of the construction programme. The utility tests include filling the ponds, testing of the inlets and outlets, neutralization of pond water and fertilizer application to the pond. These points are briefly explained here.

1. Filling the pondFilling of the pond with water should be done only after ensuring that all the construction

details are completed satisfactorily especially the inlets, by pass, silt traps and the out- lets are functioning well. Water is introduced gradually raising the heights in each pond as already planned depending on the purpose of the pond whether for breeding, spawning, hatching, nursery raising, rearing or stocking. After filling to the desired height leave the ponds for few days to check if there is any problem arising. Care should be taken to provide the type of water required whether fresh water or saline water or cold water according to the type of fish culture planned in the pond. Needless to say that if there is any defect it should be rectified before one starts using the ponds.

2. Testing inlets and outletsThe inlets and outlets are probably the most important part of a fish pond system

because it is through these that we control the water level, the inflow of desirable and undesirable water, the quality of water in the pond, safety of fish in the pond and prevent silt flow and muddy water during rainy season. The test also would include checking the effectiveness of the methods used for prevention of clogging the inlets and outlets.

3. Fertilizer application in pondsOnce the water is impounded in the ponds the next stage is to leave it for natural

generation of pond or aquatic flora and fauna. Under the warm climate within few days micro flora starts growing followed by micro fauna. This microbial growth can be increased by the addition of cow dung, pig dung or any other animal dung. However poultry dung will be too much heat generating and hence it should be added only after it is decomposed. Normally 0.5 to 1.5 kilogram of animal dung per square metre area could be added to fertilize the pond.

It is better to use the well rotten animal dung instead of fresh dung. If fresh dung is used, during the decomposition large amount of heat is produced as well as till the decomposition is over (nearly 1 to 1.5 months) the nutrients will not be available or very little will be available to the micro flora. Secondly, during the decomposition the oxygen content in the water goes down due to heat generation and organic decomposition below the required minimum amount 4 mg/litre ( 4 ppm) of water. It is to be noted that the amount of oxygen dissolved in water reduces from 9.79 to 7.48 ppm when the temperature of the water rises from 15 to 30 degree centi- grade.

4. Neutralization of waterThe optimum pH of the water in the fish pond for the optimum growth of the fishes is

between 6.5 to 9.0. If the pH i is low then add sufficient lime to bring up the pH. The amount of lime to be added in relation to pH is given here: for pH between 4-5 add 2000 kg of lime per hectare area of pond; for pH 5 to 6.5 add 1000 kg, for 6.5 to 7.5 pH add 500 add for pH 7.5-8.5 add 200 kg of lime per hectare of pond area. If the pH is very high then application of gypsum at the rate of about 200 kg per hectare can bring down the pH. Mildly alkaline water can be turned to neutral by the heavy application of organic manures and leaving the pond for a month.

IX. Conclusion

The fish ponds and other infrastructural facilities for fish farming should set up in such a way that they become a permanent asset which can generate regular income to the owner or to cultivator. They should be one time capital in- vestments which should help in regular culturing and harvesting of the fish for many years to come. Even a home level fish pond should be constructed in such a way that it becomes a permanent asset to the family to get a regular amount of income. A well established fish pond system is perhaps the most profitable farm enterprise.

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