AFRICAN CATFISH

(Clarias gariepinus)

Introduction• More than 100 species of the genus Clarias

have been described in Africa.• Teugels (1984), who recognizes only 32 valid

species.• C. gariepinus (Burchell, 1822), synonymous with

C. lazera is the most important for aquaculture.• Of secondary importance is C. anguillaris. This

species has a more restricted distribution, occuring in Mauritania, in most West Africa basins and in the Nile.

• Thus, C. anguillaris lives in most river basins sympatrically with C. gariepinus.

• African catfishes inhabit calm waters from lakes, streams and rivers to swamps, some of which are subject to seasonal drying.

Clarias lazera

Clarias anguillaris

BIOLOGY• Displaying an anguilliform shape, having an

elongated cylindrical body; dorsal and anal fins are extremely long, nearly reaching or reaching the caudal fin; both fins contain only soft fin rays.

• The outer pectoral ray is a spine.• Pelvic fin normally has six soft rays.• Head is flattened, highly ossified and the body

is covered with a smooth, scale less skin.• 4 pairs of unbranched barbels one nasal, one

maxillar (longest and most mobile) on the vomer and two mandibulars (inner and outer) on the jaw.

• Tooth plates are present on the jaws as well as on the vomer.

• Apparently has little hydrostatic function.• Buoyancy is controlled by air carried in the

suprabranchial chamber.• Clarias species have a scale less skin.• Darkly pigmented in the dorsal and lateral parts

of the body.• colour is uniform or marbled and ranges from

grayish olive to blackish according to the substrate.

• Exposed to light the colour becomes lighter.• A suprabrachial or accesory respiratory organ,

composed of a paired pear-shaped air chamber containing two arborescent structures is generally present.

• In air-situated water catfish can survive without air breathing.

• It enables them to migrate over land.• Reports of Clarias “walking” occur widely in

literature.

• C. gariepinus feed mainly on aquatic insects, fish and debris of higher plants.

• They also feed on terrestrial insects, molluscs and fruits It may be considered as an omnivorous fish with a high tendency to predation.

• The catfish grasps its prey by sunction.

NATURAL BREEDING• Ovaries of C. gariepinus are paired elongated

organs situated dorsally in the body cavity.• The lamellae contain oogonia and oocytes in

follicles at different stages of development.• Each ovary extends posteriorly into a distinct

oviduct.• Matures females have very large ovaries which

fill the body cavity and may constitute up to 25-3-% of their total body weight.

• In nature the ovaries of a mature population usually represent from 7-12% of the total body weight of females (Micha, 1973; Bruton, 1979).

• The testes are paired and connected by fused spermatic ducts which open into an elongated, posteriorly pointed, urogenetal papilla.

• The testes are externally differentiated into two distinct regions: a milkish-white, opaque anterior part, the true testes (spermatogenesis and sperm storage) and a semi-transparent posterior part consisting of a series of finger-like lobes, the seminal vesicles (glandular function).

• The testes only represent a maximum of 2-4% of the total body weight.

• The median size of fish at first maturity shows remarkable variation and ranges from 260-750 mm total length.

• Maturity was reached towards the end of the second year by most of the population.

• Under artificial conditions catfishes mature after about 6 months when they have attained a weight of about 200g.

• Feeding and water temperature are major factors regulating the age/size at first maturity.

• Eggs of mature females are -small (1.2-1.6mm), slightly oblong and

have a yellowish-green color.-nucleus in the center is clearly visible.-1 gram of stripped eggs contains

between 600- 900 eggs.• Spawning takes place mostly at night in

recently inundated marginal areas of lakes, stream or river.

• Courtship and mating take place between isolated pairs in shallow waters.

• There is no parental care for ensuring the survival of the catfish offspring except by careful choice of suitable site.

• Development of eggs and larvae is rapid and larvae are able to swim within 48-72 hours after fertilization.

• Temperature and flooding are probably the decisive stimuli for gonadal development and spawning.

Artificial Propagation and

Fry Production

ADAVANTAGES:

• Better rates of fertilization and hatching;

• protection against enemies and unfavorable environmental conditions;

• better conditions for growth and survival

Broodstock and hatchery management

• 100 males as broodstock for propagation

• 100 females as broodstock for propagation

• 100 males conditioning

• 100 males for conditioning

Breeders are kept in rectangular tanks of about 1 to 1.5m3.Water inflow is at one end, while the water flows out at the Other end througha turn-pipe.

Oxygen concentration in the water should not fall below3mg/l.

Optimum temp must be 25 degree celsius.

Adequate food supply is also of foremost importance to broodfishes.

A well balanced compounded diet containing all the essential nutrient requirement, particularly amino acids, vitamins and minerals is a prerequisite for proper gonadal development.

On-growing of African catfish

Semi- intensive polyculture of catfish and tilapia

•One way to enhance the production of tilapia ponds is to stock them together with a predatory fish such as C. gariepinus, which controls the excessive reproduction •Semi-intensive polyculture of catfish and tilapia in earthen ponds aims at minimizing inputs.

Preparation of ponds

Pond preparation is done in

the usual way. In addition the pond should be equipped with at least one compost crib placed in a corner near the inlet and made of bamboo or wooden stakes. Compost crib

Pond stocking

•Fingerlings are stocked as soon as the ponds are filled with water. The stocking rate depends on the marketable size.

•If higher marketable sizes are desired, catfish may be stocked at a lower rate, but not less than 0.5 fingerling per square meter.

Pond fertilization

•After stocking, the natural production of the pond should be regularly maintained by adding mainly organic fertilizers. Inorganic fertilizers, generally more expensive, are usually not necessary and their use should be restricted to areas with very poor soils and/or acid water.

Supplementary food distribution•While some production (up to about 30–50 kg/are/year) may be obtained only by relying on the natural pond production increased through fertilization, successful polyculture of catfish and tilapia should involve supplementary feeding.•The most economical ingredients which are locally available in significant quantities should be used. If available and economically feasible, oil cakes, which are rich both in energy and protein are preferable. They should be ground before feeding.

Hormone treatment of

broodfish

The success of the artificial propagation, depends on the number of such dormant ovocytes in the ovary. Females selected for induced ovulation and spawning should show :

• a well-rounded and soft abdomen which extends anteriorly past the pectoral fins to the urogenital papilla. Mature eggs, showing clearly the nucleus in the centre, can be obtained easily by slight pressure on the abdomen;

• a genital opening which is swollen and sometimes reddish or pink in colour.

The following hormones/compounds have been successfully used to induce artificial propagation with C. gariepinus :

• acetone dried carp pituitary, 4 mg/kg body weight (BW);

• acetone dried or fresh Clarias pituitary, 1 gland/female;

• Human chorionic gonadotrophin (HCG), 4 IU/g BW;

• Deoxycorticosterone Acetate (DOCA).

Generally the hormone solution is injected into the dorsal muscles above the lateral line, just below the anterior part of the dorsal fin, using a graduated syringe (2 – 5 ml). The needle is placed parallel to the fish, pointing posteriorly at an angle of approximately 30°.

After injection, the injected area is rubbed with one finger to distribute the hormone suspension evenly throughout the muscles. When more than 10 females are selected, it is advisable to separate them into two groups of equalnumbers and to inject them with a time interval of about 30–60 minutes between groups. This will give the operator more time for stripping the females at

the right moment. Females are generally injected in the evening. The injection time is calculated according to the water temperature and the desired time of stripping .Handling of breeders should be done with care using a wet towel. After injection, the females are gently replaced in their covered containers. There is no need to suture the genital orifice of catfish to  

prevent wastage of ovulated eggs, since the females do not scatter their eggs without the presence of a male.

be nursed in small earthen ponds for about one month up to the fingerling stage. 200 to 1 000 m2 size may vary. Rectangular ponds ranging from 10 × 20 m to 25 × 40 m. good standing crop of zooplankton must be established.non-polluted, slightly alkaline water (pH 6.5–8) and well exposed to sunlight. The water supply, (i) replace water losses due to evaporation, seepage or leakage, (ii) fill the nursery pond rapidly, (iii) exchange the water if oxygen depletion or chemical water pollution occur.

Pond Nursing of Catfish Fry

wide water supply pipe or channel. draining structure. the pond should be fenced by a fine

mesh netting or roofing sheets, height 1–1.5 m, should be embedded for about 10 cm.

The inflowing water should be filtered through a screened box placed on the inlet pipe.

The appropriate moment for stocking fry is about 3 to 5 days after fertilization.

2–3 day-old fry (two-thirds of yolk has been absorbed) or with 6–7 day-old fry, fed previously with zooplankton or Artemia.

Day Artificial propagation Nursing pond

- 4 Injection of broodfish           -

- 3 Stripping and incubationCleaning ponds: cutting grass, removal of silt, etc.

- 2 Hatching, separation of normal larvae and spoiled eggs

Liming

- 1 Cleaning larval troughs Water filling and fertilization

0           - Stocking of fry

+ 3, 7, 1014, 17, 21

          - Fertilization

+ 26–30           - Harvest

SCHEDULE FOR SYNCHRONIZED ARTIFICIAL PROPOGATIONAND POND NURSING ACTIVITIES

Once the fry are stocked, a high standing crop of zooplankton must be maintained in the nursery ponds by regular fertilization to ensure good growth and high survival.

5 kg manure, 0.1 kg nitrogen and 0.025 kg phosphorus per 100 m2 of pond.

Feeds are distributed twice a day at a rate (per 100 m2) of 0.5 kg during the second week after stocking, 0.75 kg during the third week, and 1 kg during the fourth week.

0.5–1 mm but the food composition remains the same.

After about one month, the fingerlings (weighing 2–5 g) are harvested from the nursing pond. The fingerlings are collected in a concrete or wooden harvest box fixed to the outlet pipe.

PROCUREMENT OF MILT

PROCUREMENT OF MILT

- Milt is obtained by sacrificing one male and dissecting the testes.

-milt can then easily be squeezed out and collected into a small bottle.

FERTILIZATION OF EGGS

FERTILIZATION OF EGGS

-a few drops of milt solution are added into the eggs and the sexual products are mixed by gently shaking the bowl.

-physiological salt solution is added.

-the eggs are fertilized by adding a small amount of clean water.

INCUBATION AND HATCHING OF EGGS

INCUBATION AND HATCHING OF

EGGS

-fertilized eggs are incubated in stagnant or running water in troughs containing small trays or boxes.

-incubator is filled with clean, well oxygenated water.

INCUBATION AND HATCHING OF EGGS

Nursing of Early Fry•After 3-4 days, when about two-thirds of the yolk sac has been absorbed, the larvae (weighing about 2-3 mg) become early fry.•Once the yolk sac is fully absorbed, the fry must find adequate food to ensure proper development•During the early stage the development of the main organs will be completed after 10-18 days when the accessory air-breathing organ has developed.•Catfish fry (weighing 30-50 mg) frequently rise to t he surface to breathe air. They become then advance fry.

Hatchery Nursing of Early Fry

• Early fry are kept in the larval rearing troughs, and the rearing troughs•Catfish fry have been nursed successfully with the following first feed:(1) live or frozen zooplankton (2) live or frozen nauplii of brine shrimp Artemia salina; (3) decapsulated Artemia eggs.•A variety of artificial dry feeds such as complete diets, commercial trout starters, microencapsulated egg diet, etc. have been tested- result: the food intake was considerably reduced especially a few days after initial feeding; growth was poor and mortality high.

• Recently rather good growth and high survival have been obtained using an artificial dry feed. This feed, containing 55.4 % of crude protein. Unfortunately this type of yeast is not available in most African countries.

• Feeding live zooplankton from nearby fresh water fish ponds seems to be the most reliable technique for African countries, since importation of Artemia eggs is either difficult or prohibited.

• Feeding every 3-4 hours during 24 hours is even better.

•Hungry fry swim vigorously in the water column, whereas well-fed fry gather in clusters on the bottom of the tank and have a considerably swollen belly.•The stomach contents of the fry can easily be monitored since their ventral sides are transparent.•Thus fry fed on Artemia nauplii or decapsulated Artemia eggs have a distinct orange belly after feeding.•Mortality during the early fry stage is negligible under optimum nursing management.

Hatchery Nursing of Advanced Fry

• The early fry stage ends when the fry fill up their supra-branchial air chamber with air.

• The advanced fry are transferred to nursery troughs. Water depth is increased to 0.5m.

• Transferring of advanced fry is a delicate procedure, and must be done by carefully siphoning fry into bucket. The contents of the bucket are then gently released into the nursing device.

• Each nursing trough, filled with 160-200 L of water, may be stocked with 10,000 fry (50 to 65 fry/L).

• The water supply must be adjusted once a day according to the dissolved oxygen content of the outflowing water. The recommended minimum dissolved oxygen level for advanced fry nursing is 3 mg/l.

FEEDING• There are several physical and

chemical requirements for artificial dry feeds. 0.35-0.5 mm for fry of 50-100mg 0.5-0.75 mm for 100-250 mg fish 0.75-1.25 mm for 250 mg-1 g fish

• From 10-18 days after hatching the fry will accept artificial diets. The change from live food to artificial dry feed is a major turning point in the life of hatchery nursed catfish.

• Artificial feed can be administered manually (6 times a day) or automatically with feeders. Over feeding must be avoided since this is believed to be the main cause of disease outbreaks at this stage of development.

• After 5-8 weeks, the advanced fry will weigh about 1 g. at this size, they can be harvested and transferred to fattening ponds. A survival of about 70-80% can be obtained under optimal husbandry management.

• Yolk Sack Larvae - Yolk sack larvae are 3 day old, free swimming larvae that require their first food shortly after receiving.  Yolk sack larvae are suitable for stocking into plankton ponds or can be raised in tanks.  Advanced larval rearing experience and appropriate facilities are required if tank- rearing is going to be attempted.

• We pack up to 50,000* yolk larvae per box.  Minimum order 300,000 tails