In captivity the African Catfish does not spawn spontaneously since the environmental factors as rise in water level and inundation of shallow areas does not occur at the fish farms. Since the early 70's several techniques have been developed (with or without hormone treatment) for the artificial reproduction of the African catfish.
Mature breeders can be reproduced artificially by simulating the events which will occur in the rainy season and which triggers the mating and spawning processes. Ponds with an approximate size of 400 m2 are filled with 25 cm of water and stocked with 6 mature females and 4 males. A few hours later the water level is raised up to a level of 50–60 cm. Spawning will occur at night and the following morning the breeders can be removed.
Theoretically this techniques is artificial reproduction as some offspring is produced. From a practical point of view it is not as the number of fingerlings which can be harvested after 6–8 weeks is low (1–2 fingerlings/m2).
For hormone induced reproduction (semi artificial or artificial) the following hormones are in general used.
DOCA (Desoxycorticosteroid Acetate, 2.5–5 mg per 100 gram of female. A disadvantage of this hormone is that it is mostly suspended in oil which causes severe ulcers at the injected female.
HCG (Human Chorionic Gonadotropin), 25 I.U. per 100 gram of female. This hormone works well but it is very expensive.
Common carp pituitary gland material, 3–4 mg per kilogramme of female or 1–2 whole pituitaries per female. In general the common carp pituitary gland material has to be imported from abroad which means that it is not accessible for small fish farms.
Pituitaries of the African catfish. A female catfish will respond once it injected with a pituitary of a catfish (male or female) of equal size.
pituitaries of the Nile Tilapia (Oreochromis niloticus), 3–4 pituitaries of a Nile Tilapia (100–150 gram) per female catfish will induce ovulation.
At the stations of the project the last two kinds of hormonal material are used with success and during the training course it will be tested if pituitaries of the Nile Perch can also be used as they can be easily obtained from the various processing plants in Kisumu.
Three techniques of semi-artificial reproduction have been developed;
Mature females are injected with hormones in order to provoke the mating and spawning processes and are placed in completely filled ponds at a density of 2 females and 1 male per 100 m2. Spawning will take place in the night after the hormone treatment and the breeders are removed the following morning.
Mature females are injected with hormones in order to provoke the mating and spawning processes and are placed in a happa of 2–3 m3 (made of mosquito netting with mesh size 0.5 mm) which is placed inside a pond. Spawning will take place at night and the breeders are removed the following morning. A advantage of this method is that the eggs are concentrated in the happa were eventually they can be treated against fungal attack and that they can be easily collected after the yolk sac has been absorbed.
This technique has been used the last year at several station managed by the project. Mature females are injected with pituitaries of Catfish or Nile Tilapia and are placed together with a male in a concrete tank. The bottom of the concrete tank is covered with a layer of stone gravel which function as substrate for the released egg. The breeders will spawn in the night after the pituitaries are injected. The fertilized eggs will stick to the gravel and the following morning the breeders are removed from the tank. The fertilized eggs remain in the tank and hatching takes place and after 3–4 days approximately 5000 larvae per female can be collected from the tank. The disadvantages of this method are;
Brood fish often injure each other sometimes ending in the dead of one of the breeders.
The number of larvae obtained is relatively small as the ovulation is often partial (the quantity of eggs released is 5–10% of its body weight which is substantial less as 15–20% which is obtained through stripping) and as fertilization processes can not be controlled.
Semi natural or hormone induced reproduction in ponds/tanks as describe above has not proved to be a reliable method for mass production needed for large fish farms or distribution centres of catfish fingerlings. Therefore artificial propagation under more controlled condition, stripping of the eggs, collection of the sperm followed by fertilization of the eggs has been developed.
The artificial reproduction of the African catfish, as for all fin-fishes, is a chain of activities which is more or less similar to that of natural reproduction. It starts with the selection of broodstock from nature or from the broodstock ponds after which they are transferred to the holding tank in the hatchery. Ideal broodfish weighs between 300–800 grams, Larger fish are difficult to handle, resulting in a substantial losses of eggs prior to stripping. Mature broodfish are selected according to the following criteria;
A well distended, swollen abdomen from which ripe eggs can be obtained by slightly pressing the abdomen toward the genital papilla. Ripe eggs are uniform in size and a experienced hatchery operator can see the nucleus as a small dark point in the centre of the egg.
A swollen, sometimes reddish or rose coloured genital papilla.
Note: From a practical point of view can be stated that all females are “ripe” once some eggs can be pressed out and if the eggs are more or less uniform in size (just put some of the eggs on the nail of your thumb and add a few drops of water and look).
The most common technique to induce final maturation and ovulation in the African catfish is to inject the female with hormones or pituitary gland material (the dosages and advantages/disadvantages are discussed in para 5.2).
The required quantity of powdered acetone dried pituitary material or the number of whole pituitaries are pulverised in a porcelain mortar. Then, the required quantity of 1 ml per fish of physiological salt solution (9 gram of common salt in 1 litre of water) is added. A syringe is filled with the suspension and the injection can be given.
The most common method to administer the hormone solution, is a injection intramuscular into the dorsal muscle.
Note: fill the syringe, put the needle on it and empty the syringe again into the mortar, when this is possible you can start to inject the fish. This procedure has to be followed as often the needle gets blocked by pituitary material which is not completely crushed and it is unpleasant for the fish and annoying for the operator to resolve this problem once the needle is stuck into the fish.
The process of final maturation and ovulation of the eggs will start after the administration of the hormonal material. The speed of the process is dependant on the water temperature, the higher the temperature the quicker the eggs ovulate. The relation between the temperature and the time it takes for the eggs to ovulate is presented in Table 1.
Table 1: The time interval between injection and stripping of the female catfish and the time interval between fertilization and hatching of the eggs in relation to temperature
| WATER TEMPERATURE (°C) | TIME BETWEEN INJECTION AND STRIPPING (H) | TIME BETWEEN FERTILIZATION AND HATCHING |
|---|---|---|
| 20 | 21 | 57 |
| 21 | 18 | 46 |
| 22 | 15.5 | 38 |
| 23 | 13.5 | 33 |
| 24 | 12 | 29 |
| 25 | 11 | 27 |
| 26 | 10 | 25 |
| 27 | 9 | 23 |
| 28 | 8 | 22 |
| 29 | 7.5 | 21 |
| 30 | 7 | 20 |
Stripping of the female spawners is done by gently pressing their abdomen with a thumb from the pectoral fin towards the genital papilla. Ovulated eggs will flow out easily in a thick yet from the genital vent if the females responded well to the hormonal treatment. The ovulated eggs are more or less transparent, flattened and a gram of egg contains approximately 6003 eggs. Under normal condition a “ripe” female ovulate a quantity of eggs which equals to 15–20 % of her own body weight. If the fish is stripped to early the eggs are coming out difficulty and they have a “flushy” appearance if they are stripped to late.
Note: The temperatures at the several stations is rather fluctuating, with higher temperatures at day time. It looks like it that the eggs are stripped to early which results in very low hatching percentages (5–10%). It is always much safer to strip the egg to late then to early because if you are to early you will lose all your eggs, if you are to late you will loose some eggs.
The males of the African catfish cannot be stripped and consequently the sperm can
only be obtained by sacrificing a male.
The male is killed and thoroughly dried after which the testis is dissected and placed in a glass
and cut quickly into small pieces with a scissor and finally the milt is pressed out with a pestle
or a teaspoon.
The sperm and pieces of testis material is added to the stripped eggs. Then, the eggs are fertilized by adding about the same volume of clean water. The water and egg mass are mixed by gently shaking of the bowl.
Note: Stirring of the egg must be continued until the eggs are placed in the hatching tanks as the eggs become sticky and without stirring the will stick together in one clump.
After about 60 seconds fertilization has taken place and the sperm has lost its activity and the fertilized egg are ready for incubation in tanks or happa's.
With this method it is not necessary to preserve or dilute the sperm in a physiological salt solution. Once large number of females are needed to be stripped at one morning (5 or more) it is an advantage to take the sperm first and preserve it in a 0.9 saline solution.
Note: First a female is stripped and then the milt of the male is taken. One drop of water in the bottle with sperm will destroy the sperm completely while one drop of water in the bowl of eggs will only destroy some eggs.
The development process from fertilized egg to hatching is as all processes in fish dependant on the water temperature. The higher the water temperature the quicker the eggs are hatching. The relation between the water temperature and the incubation time of the eggs is presented in Table 1.
A general principle of egg incubation is that water is renewed in order to provide oxygen and that after hatching the new born larvae are separated from the remaining egg-shells and dead eggs. Otherwise the hatchlings will be infected with the fungi and high mortalities will occur. The following incubation techniques were shown and tested during the training;
The eggs are spread out on the bottom of a concrete basin. This method has works well but it has the disadvantage that dead eggs/egg-shells are not separated from the hatchlings. Daily treatment with 0.1 ppm4 malachite green is needed in order to prevent heavy outbreak of fungal infections.
The eggs are spread out on a screen which is placed on the bottom of a concrete basin. This method works well if a screen with a mesh size of 1 mm can be obtained (which is not the case at present) then the hatchlings will pass the screen and the dead eggs and shells remain on the screen. By removing the screen out of the basin a separation between hatchlings and dead eggs is made.
The eggs are “sticked” to the roots of water hyacinth (Eichhornia crassipes) which floats inside a happa made of mosquito netting (mesh size 0.5 mm) which is placed inside a concrete basin. This method has been developed by the FAO project in Congo Brazzaville (de Graaf et al., in press, Annex 1). The investments are low (100–200 shilling per happa) and hatchlings are separated well from the dead eggs as long as the distance between the roots of the water hyacinth and the bottom of the happa is kept at 15–20 cm. At hatching the larvae sink to the bottom of the happa and the egg shell remain sticking to the roots of the water-hyacinth. In Kenya it is not recommended to use water-hyacinth as it is government policy to ban this plant (which occurrence is a disaster in many countries of Africa because of it high growth it cover lakes, streams and irrigation channels completely) and it is not allowed to transport it.
The eggs are sticked to the roots of nile cabbage/water lettuce5 (Pistia stratiotus) which floats inside a happa which is placed in a concrete basin. The nile cabbage works as well as the water hyacinth. It floats well, it has a well developed fine root system and the eggs stick nicely. The nile cabbage is not a “waterpest”, it is easy to found and its use is therefore recommended.
The eggs are sticked to a brush which floats inside a concrete basin. This method works very well the eggs are completely under water the only disadvantage is the price of the brush (50 shilling per piece).
The eggs are sticked to submerged waterweeds and placed inside a happa which is placed inside a concrete basin. Large number of eggs can be “sticked” within seconds to the submerged weeds. The disadvantage however is that the weeds sinks to the bottom of the happa. After hatching the larvae are hiding in the water weeds and it takes considerable time to remove the weeds in such a way that no larvae will be removed also
The eggs are sticked to bundles of sisal placed inside a happa. The sisal bundles were under water by means of a iron nut. The eggs stick well to the sisal6. The disadvantage is however that only a limited number of eggs sticks to one bundle of sisal as the sisal fibre stick all together once the are in contact with the water.
The eggs were sticked to the top/flowers of papyrus and placed inside a happa in a concrete basin. This method does not work well as the eggs do not stick well to the papyrus flowers.
The eggs were spread out on the bottom of a happa of 1m3 which was placed in a pond. This method works well but it is recommended to treat the eggs daily with 0.1 ppm malachite green.
4 ppm = parts per million or 1 mg/litre
It is possible to incubate the eggs and hatchlings in stagnant water (oil drums/barrels) but a low egg/hatchling densities is essential and should not exceed 100–150 per litre (or 0.1 gram of eggs per litre).
The hatched larvae (1–1.5 mg) are kept in the incubators and do not have to be fed as their food resource is the yolk sac. After 3–4 day the yolk sac will be absorbed and the hatchling developed into a small catfish which is in need of zooplankton for its further development and survival and further nursing is done in earthen ponds.
