Breeding Methods and Technical Key Points for the African Sharptooth Catfish

I. Classification and Distribution:
The African sharptooth catfish, also known as the Egyptian catfish or leathery sharptooth catfish, is native to the Nile River system in Africa. China introduced it for trial breeding in 1981, and in 1982 the Guangdong Freshwater Breeding Farm succeeded in self-propagation. It has now been promoted across most of South China and Central China. In Guangdong and Guangxi it is one of the high-yield freshwater aquaculture species.
　　
II. Biology and Ecology:
Taxonomically, the African sharptooth catfish belongs to the family Clariidae, genus Clarias. The body is cylindrical, with a flatter head than the local sharptooth catfish and a more elongated body; the mouth is slightly subterminal, the barbels are well developed, and the eyes are relatively small. The top of the head and back have many bony granular protrusions arranged in a radiating pattern; the fin ray margins are pale red; the sides of the body have black spots and grayish-white cloud-like patches; the chest and abdomen are white; and the mouth cleft is relatively wide. Gill rakers number 52-90, dorsal fin rays 65-76, pectoral fin rays 8-9, anal fin rays 52-55, pelvic fin rays 1-5, and vertebrae 58-62. Body length is 7-8.8 times body depth, and 4.6-5.2 times head length; head length is 1.1-1.5 times body depth, and 2.8-3.2 times snout length.
1. Living habits: The African sharptooth catfish is a bottom-dwelling fish with a docile temperament. It has strong environmental adaptability, with a critical low-temperature tolerance of 7°C. It tolerates low oxygen, and can still survive when dissolved oxygen drops to 0.128 ppm; when dissolved oxygen in the water is insufficient, it often swims to the surface to gulp air. Intraspecific competition is relatively intense; in fingerling ponds and grow-out ponds, the strong preying on the weak and mutual killing frequently occur.
2. Feeding habits: The African sharptooth catfish is an omnivorous fish that mainly feeds on animal-based bait. It is voracious, eating plant-based feed but preferring animal-based feed, and its growth rate is faster when fed animal-based feed. In natural waters, it mainly feeds on small fish, small shrimp, aquatic insects, aquatic earthworms, benthic organisms, and so on. In artificial culture, it can be fed wild trash fish, silkworm pupae, fly maggots, mussel meat, discarded slaughterhouse offal, and so on; it can also be fed artificial compound feed such as wheat bran, flour, soybean cake, and so on, or these feeds can be made into extruded pellet feed with better results.
3. Reproductive habits: The African sharptooth catfish reaches sexual maturity at one year of age, with the smallest sexually mature individual weighing about 100 g. The breeding season is from April to October, with the optimal breeding period from early May to early July, and the optimal breeding water temperature is 25-32°C. It can naturally spawn and reproduce in ponds; its spawning habit resembles that of the common carp, laying adhesive eggs. Broodfish tend to nibble on egg masses, so the spawned eggs should be collected and hatched as early as possible.
The African sharptooth catfish is a multiple-spawning type; after spawning, broodfish that are intensively conditioned for about 1 month will have their gonads develop and mature again, and they can be induced to spawn 4-5 times a year. Fecundity is relatively high: a broodfish weighing about 500 g can lay about 10,000 eggs each time.
4. Growth rate: The African sharptooth catfish grows relatively fast; fry hatched in the same year can reach market size in that same year, generally reaching 500-700 g per individual, with the largest individuals reaching 1.5-2.5 kg. In pond monoculture, with sufficient feed supply, yield per mu can reach as high as 1,500-2,500 kg; in polyculture, yield per mu generally reaches 75-100 kg.
　　
III. Breeding Techniques
1. Broodfish conditioning:
(1) Broodfish pond: Use an ordinary fish pond as the broodfish pond, with an area of 1-2 mu and a water depth of 1.5 m. The pond bottom should be flat for easy harvesting, with a good water source and convenient drainage and irrigation. Before stocking broodfish, the pond must be cleared and disinfected, and the pond bottom and dikes checked for leaks to prevent fish from escaping.
(2) Stocking density: It is appropriate to stock 150-250 kg of broodfish per mu (100-150 pairs). The broodfish stocking density varies with water quality; too high a density affects gonadal development.
(3) Feed and daily management: The feed is mainly peanut cake and soybean cake, supplemented with fishmeal, silkworm pupae, fly maggots, fresh fish meat, or discarded animal offal, and so on. In the month before entering the reproductive period, animal-based bait should be the main feed to promote gonadal development. The daily feeding amount is 10%-15% of body weight, fed in two portions in the morning and afternoon. New water should be added 1-2 times per week, for 2-3 hours each time.
(4) Broodfish overwintering: The African sharptooth catfish is a tropical fish, and its tolerance to low temperature is higher than that of tilapia. When the water temperature drops to 10-15°C, it begins to enter the overwintering period. Underground hot water, hot spring water, air-raid shelters, earth-built underground greenhouses, or waste hot water from factories can all be used for safe overwintering.
2. Sex characteristics and maturity of female and male fish:
Female fish have relatively abundant mucus on the body surface, lighter pigmentation, and slightly fewer black spots on the sides of the body. The abdomen is plump, the external genital papilla is short and rounded, the urogenital pore is a long slit, the genital papilla is far from the origin of the anal fin, and its color is pale red. Male fish have a rougher body surface, darker black body color, and prominent black spots on the sides of the body. The abdomen is not plump and is firm, the external genital papilla is elongated, the urogenital pore is round and small, opening at the end, and the external genital papilla extends backward beyond the origin of the anal fin.
Mature female fish show an ovarian outline in the abdomen, which feels elastic and soft when touched by hand, and sometimes emerald-green eggs can be pressed out; the genital pore is tubular, the anus is slightly protruding, and sometimes red and swollen. Male fish have a straight body, rarely with abdominal swelling; the genital pore is a slender tube with a relatively pointed end, extending to the base of the anal fin, and the anus is slightly sunken and sometimes slightly red.
3. Artificial breeding techniques:
(1) Selection of broodfish for induced spawning: The African sharptooth catfish can reach sexual maturity at 1 winter of age and a body weight of about 100 g, but broodfish for induced spawning should be selected from individuals weighing more than 250 g, raised for 1 full year, robust in constitution, and free of disease and injury. Mature female fish have eggs of uniform size, appearing emerald green. If the eggs are of uneven size or mushy, these are characteristics of immaturity or over-maturity.
(2) Conditions of the spawning pond: A square cement pond of several dozen square meters is most suitable as the spawning pond, with a depth of about 50 cm, stocking 15-30 pairs of broodfish per pond. The water quality of the spawning pond should be fresh and clear; river water or purified tap water can be used, with the water depth maintained at 20-30 cm. Spawning nests must be set up in the spawning pond; spawning nests are divided into sinking and floating types. Floating spawning nests can use the root fibers of water hyacinth, while sinking ones can use palm, willow roots, or hornwort, and so on. The density of spawning nests should basically cover the entire water surface, and a certain number of spawning nests should be placed on the pond bottom to reduce eggs sinking and adhering to the pond bottom. Spawning nests should be soaked and disinfected in 25% salt water before use.
(3) Sex ratio, density, and management of broodfish: The sex ratio of broodfish should have slightly more males than females, with a female-to-male ratio of 1:5 being suitable. A broodfish spawning group of 3-6 fish per square meter of water surface is ideal. To prevent broodfish from jumping out during courtship and spawning, netting or bamboo mats can be used as cover. The surroundings of the spawning pond should be kept quiet; otherwise it will affect broodfish spawning.
(4) Induced spawning dose and effect time: Artificial induced spawning of the African sharptooth catfish is suitable as a single injection, and the inducing agents should preferably be carp pituitary or chorionic gonadotropin; using the two in combination gives better results. The general dose is 2-3 carp pituitaries plus 500-800 international units of chorionic gonadotropin per kg of female fish, and the dose for male fish is 1/3 that of female fish. If carp pituitary is used alone, use 5-6 per kg for female fish and 1-2 for male fish. From induced spawning to broodfish courtship and chasing takes 3-4 hours, and to spawning takes 10-16 hours. The effect time varies with changes in water temperature.
(5) Treatment of broodfish during egg collection: From the discovery of broodfish spawning to the cessation of spawning generally takes 3-4 hours. Therefore, 3-4 hours after spawning, the fertilized eggs together with the spawning nests should be quickly moved out and spread out for hatching. At the same time, the broodfish should be caught and removed so they can mature again. Care must be taken when catching broodfish to avoid damaging the eggs in the pond.
4. Artificial hatching: Hatching can be carried out in small mud ponds, net cages, or shallow ponds enclosed with plastic film, wooden boards, and so on. For still-water hatching, 20,000-30,000 eggs can be accommodated per square meter of water surface; for flowing-water hatching, the density can be increased. The key to hatching is maintaining fresh water quality and controlling the water level. According to experiments by South China Normal University, hatching with purified tap water achieved a hatching rate as high as over 90%; hatching with fresh pond water achieved about 80%; while using turbid well water or fertile water achieved only 30%-50%. The hatching water level should not exceed 0.5 m, with about 30 cm being suitable. During hatching, direct sunlight should be avoided, and the temperature difference between day and night should not be too large. For net cage hatching, the net cage must be cleaned frequently. At a water temperature of 22-25°C, hatching takes 26-36 hours; at 25-26°C, it takes 22-25 hours; at 27-30°C, hatching takes 21-22 hours.
　　
IV. Fry Rearing:
1. Cement pond fry rearing: Cement ponds are generally built square, generally with an area of 10-20 sq m and a pond height of about 1 m. For fry stocking density, if rearing to about 3 cm, stock about 2,000 fry per square meter. With sufficient feed, after about 15 days of rearing they can reach the size for pond release, and the fry survival rate is relatively high.
The technical key points for rearing fry in cement ponds are:
(1) Strictly control water quality and water level, frequently change and add new water, keep the water fresh and clear, and keep the water depth no more than 30 cm.
(2) Feed reasonably. Start feeding 2 days after the fry hatch. In the first few days of feeding, filtered (50-mesh standard sieve) water fleas and duck egg yolk can be used, fed 2-3 times a day; the daily amount is one duck egg yolk per 10,000 fry, splashed along the pond edge. After 4-5 days, switch to aquatic earthworms or a mixed feed made of fishmeal (60%), flour (30%), and pupa meal (10%); each feeding amount should be based on what can be eaten within 5 hours, fed twice a day.
(3) Divide the ponds in time to prevent increased density and fry gasping for air at the surface due to lack of oxygen.
(4) Prevent direct exposure to sunlight.
2. Net cage fry rearing:
The net cage size should preferably be 10-20 sq m. The mesh size should match the size of the fry. The net cage is set in a pond with fresh, clear water. The stocking density is about 10,000 fry per square meter. Feed supply is the same as for cement pond fry rearing. Daily management should include frequently cleaning the net cage to prevent mesh clogging and ensure smooth water flow.
3. Plastic film pond fry rearing:
Use wooden boards to enclose a rectangular wooden frame on the ground, line it with a layer of plastic film, with a pond depth of 15-20 cm. Use purified tap water, and stock 10,000-15,000 fry per square meter. The rearing and management methods are the same as above.
4. Pond fry rearing for "flowering": Rearing African sharptooth catfish fry by pond "flowering" is basically similar to that of the four major Chinese carps; the bait source mainly relies on artificially cultured zooplankton, supplemented with artificial bait. The pond area for "flowering" should preferably be about 0.3-0.5 mu, requiring water that is fertile yet fresh and clear, with abundant bait organisms. The "flowering" density is 100,000-150,000 fry per mu. Other management methods are the same as for cement pond rearing.
　　
V. Grow-out Culture Techniques
1. Large pond polyculture: This is a relatively common culture method. That is, in an ordinary pond, keep the original species, size, and density of Chinese carp fingerlings unchanged. Several months after the carp are stocked (that is, July-August each year), stock 200-500 African sharptooth catfish fingerlings (size 3-5 cm) per mu of pond. The culture method follows the usual common feeding and management.
2. Monoculture: Rural household fish farming can use small water bodies for high-yield culture, and monoculture can be used. It can be cultured twice a year: the first time stocking in May and harvesting in August, and the second time stocking in August and harvesting in December. The monoculture pond area is not restricted; 50-100 fingerlings of 3-5 cm can be stocked per square meter of water surface. Feed can be dead fish, earthworms, dried silkworm pupae, animal viscera, swill and leftover rice, or peanut bran, or freshwater fishmeal 60% + flour 20% + rice bran 15% + pupa meal 5% (fishmeal can be replaced by meat paste of animal-based feed). For early-stage young fish, the bait should be fine, and a mixture of 80% fishmeal and 20% flour can be used. In the later stage, coarse feed should be the main feed, and a certain amount of poultry and livestock manure can be added to reduce production costs. Feed 1-2 times a day, with the daily feeding amount accounting for 5%-10% of the fingerling weight. The feeding amount should be increased or decreased according to weather, water quality, and the fish's feeding situation, with the appropriate amount being what can be eaten within a few hours each time.