African Catfish (Clarias gariepinus)
African Catfish (Clarias gariepinus)
INTRODUCTION TO AFRICAN CATFISH HATCHERY SET UP AND MANAGEMENT
In Europe, Clarias gariepinus was first introduced in the Netherlands in 1976. The first brood stock originated from the wild from 40 African catfish transferred from the Central African Republic (Hogedoorn and Vismans, 1980). Commercial farming of this species started in 1985 in recirculation aquaculture systems (RAS).
Much later catfish strains from Israel and the Republic South Africa were introduced. These strains were crossed for the production of fingerlings and resulted in the currently cultured “Dutch strain” African catfish.
On farmers level brood stock selection is mostly done in a very primitive way. To hold and monitor large populations of different African catfish strains strictly separate for long periods is very costly. The results are, if you are successful, visible after a couple of years and the next problem for the commercial farmer is keeping this advantage for him selve!
Another problem for the farmer producing African catfish fingerlings is to show his customer the benefit of an improved strain. Improvements in growth and feed conversion ratio of for example 5% are great achievements in the mind of a researcher, but for a farmer small differences and most probable not spotted without serious farm recordkeeping.
Practically spoken the market for African catfish fingerlings is first of all price driven. Next to this hatcheries focus on availability, size, uniformity and health status of the African catfish.
Most African catfish farmers (tropics and Europe) are small to medium sized farmers, not well organised, and simply do not have the means and abilities to do serious research on genetic improvements of their stocks. The little research done on African catfish genetics is done by universities but has never been seriously implemented in practice.
SELECTION OF AFRICAN CATFISH BROODSTOCK
African catfish farming is a relatively new industry. In Europe it started in the early eighties and in Africa only few farmers were active in an extensive way by that time.
The first broodstock came from the wild. In the Netherlands for example, wild African catfish was imported from Central Africa and the first generations the selection was based on growth. My personal opinion is that we were just performing selection of fish which were able to adapt to the intensive way of farming in warm water recirculation systems. Soon after the introduction of African catfish from Central Africa fish was brought in from Israel and RSA. In the Netherlands the strains were not kept separate and as a result the “Dutch African catfish” is a result of 3 strains.
Meat quality and dress out percentage are very important parameters for the processing industry. Variation is noticed between the strains from different locations in Africa. In the tropics the aspect of meat quality and dressing percentage are of less importance because the fish is consumed as a whole; no filets are taken from the fish and heads and intestines are not wasted.
HYBRIDISATION OF AFRICAN CATFISH
Within the family of Clariidae (Siluriformes) intergeneric hybrids were produced through interbreeding between species from the genera Heterobranchus and Clarias (Ref.). A well-known intergeneric hybrid is a crossbred between the Heterobranchus longifillis female and Clarias gariepinus male, the so called “Hetero-clarias”. Due to rearranging of genetic material from both species in the offspring, the intergeneric hybrids show characteristics of both parental species. A well known hybrid is the cross between a Heterobranchus longifillis female and a Clarias gariepinus male, called Heteroclarias .
In our hatchery in the Netherlands we are producing this hybrid for a group of farmers linked to a processing plant. This group is very keen in producing and marketing this type of fish. The filet of Heteroclarias is white in comparison with the pink/reddish colour of Clarias gariepinus filets and contains 30% more fat than Clarias gariepinus filets, which improves the taste. The gonads of hybrids are almost absent and not active. For this reason the dressing percentage is relatively high compared to Clarias gariepinus. The Heteroclarias fish filet can be used as an alternative for white filets from marine fish species.
As a fingerling producer of Heteroclarias we notice big differences in behaviour with the common African catfish. The Heteroclarias fingerlings show a wide variation in growth and severe cannibalism is noticed, especially when frequent grading is neglected. Next to this the Heteroclarias is easily stressed. After an age of 12 weeks, well graded fish show very equal growth and low mortality to the moment of harvesting at 1.4 kg.
In the tropics the Heteroclarias is considered superior over the Clarias gariepinus in growth in pond culture and is considered as better growing fish.
For a fingerling producer hybridisation has a major benifit. The hybrids are infertile and it is not possible for customers to continue breeding with those fish. The pure parent stock is kept on farm and is never shared with other farmers. The pure Heterobranchus longifillis strain matures at a age of 2 years, which is very late compared to Clarias gariepinus (1 year).
AFRICAN CATFISH BROODSTOCK MAINTENANCE
The purpose of good brood stock maintenance is to harvest good quality eggs and sperm. The brood stock should be individually tagged to have tracability for each batch of offspring and to have the possibility for a breeding programme. Th broodstock should be given enough time to recover from spawning and with the individual tagging it is possible to do proper record keeping.
Brood stock should be kept separately from other farm activities for obvious reasons:
To keep them away from stress and diseasesTo optimise their environment by constant light regime and constant water quality, to achieve whole year reproductive cycle
We prefer recirculation systems in a confined area with temperature control if necessary. In the tropics flow through systems can work too, if flushed with good quality bore hole water.
PRODUCTIVITY OF FEMALE BROOD STOCK
In our farm the productivity of the female (fecundity) expressed as % of the body weight is between 5-15%. The egg size tends to increase with the size of the female. In larger fish the number of eggs per gram of eggs is lower than in smaller broodstock. On average we count 500 eggs per gram. The average females we are using in our farm have a weight of 6 kg and produce 300-600 gram of eggs (150.000-300.000 eggs).
Egg production of African catfish
A female is selected from one of the broodstock tanks. With a small tube it is possible to sample the eggs out of the ovaries to check if the nucleus has migrated to the side and the egg size has a diameter of 1 mm or above. Most farmers do not perform this check, they just select by eye.
In captivity females do not perform final ripening of the eggs without hormonal treatment. The injection of gonadotropin releasing hormone in the form of natural pituitary glands or synthetic products like OVAPRIM induces the final step of ripening called vitelogenisis. In this final step the eggs are provided with yolk and take up water.
The period between injection with hormones and stripping of the eggs depends on the temperature of the water and the type of hormone used. Through trial and error the perfect time for stripping can be determined. Too early or to late stripping results in bad egg quality and thus poor spawning results.
Too early stripping: very dry egg mass. It is difficult to completely strip the female because the eggs do not flow out. The female often dies because of the stress and internal injuries. Too late stripping: the egg mass is fluid. Often the female has released a lot of eggs in the preparation tank already and stripping is very easy.
Stripping an African catfish female
Several hours after stripping we perform final stripping to remove all ripe eggs from the ovaries of the female. This is to prevent that these ripe eggs die inside the ovaries and start to deteriorate. This will harm the fish and can cause death of the broodstock female. The females have to stay in recovery for a couple of days before putting them back to the broodstock tank.
PRODUCTIVITY OF MALE BROOD STOCK
Sperm Harvesting
Male Clarias gariepinus do not release sperm after treatment with hormones like many other fish species. The males have ripe sperm all year round. The fish should be at least 1 year old to have ripe gonads. A lot of variation can be seen between males of the same age in ripeness and size of testis. In practice farmers sacrify males in order to dissect the testis out of the abdomen. By making incisions in the testis tissue the sperm can be collected. As a consequence new male broodstock needs to be added to the broodstock population sacrificing the males is a big constraint on genetic programmes.
Some farmers are using operation on the males. After tranquilizing the fish, a small incision is made in the belly of the fish and with a syringe with needle some sperm is taken out of the testis. Finally the incision in the belly is stitched using veterinary stitching materialand the male is able to recover in 1 to 2 weeks. During this time the wound closes completely.
Unlike the sperm of mammals sperm of fish is not active, but will become active as soon as it is in the water. The sperm is active for less than a minute, so it has to find an egg quickly before all the energy has gone. This is the reason that during the proces of sperm collection all materials, hands and the fish should be dry. Although these precautions are taken, the sperm can be activated accidently. The sperm concentration of good males is more than a million per ml!
Cryo conservation of sperm has been done on an experimental scale by Universities and the method is quite successful. The problem of this method for farmers is that they have to be equipped with a laboratory and should have permanent availability of liquid nitrogen to keep the sperm preserved.
FERTILISATION OF AFRICAN CATFISH
The eggs and sperm are collected in a dry glass or porcelain bowl and a dry small glass or porcelain cup respectively. A simple but effective way of fertilization is to bring the eggs and sperm together in the egg collection bowl, mix it gently before adding water.
In literature adding certain fertilizing solutions during fertilization is reported as being very benificial, because they are thought to extend the life of the sperm in order to improve the fertilisation rate. I prefer not to use any extra fluids because any extra handling can give a problem too.
Artificial propagation of African catfish is a relatively simple procedure and many farmers are very skillful in doing it. Millions of larvae are hatched weekly in a country like Nigeria but until today there still is a shortage of good quality fingerlings and juveniles. Reproduction of African catfish is following a certain procedure, but farming the larvae for 1 or 2 months to juvenile stage comes down to the capabilities of the individual farmer.
INTRODUCTION TO THE AFRICAN CATFISH HATCHERY
African catfish hatcheries in general can be very profitable, provided it has a good culture system and dedicated hatchery staff. Because many farmers lack knowledge, proper management ideas and/or a properly build hatchery, the results between farmers can vary from 200 eggs needed for 1 juvenile to 5 eggs needed for 1 juvenile (an African catfish juvenile being a 2 month old fish of approximately 8 grams).
In Europe African catfish hatcheries are strictly equipped with recirculation systems (climate conditions do not allow to do otherwise). In the tropics hatcheries are either recirculation systems only or a combination of recirculation systems, flow through systems, and small ponds.
In many African countries the juvenile production is by far not meeting the demand. This results in high prices and often inferior quality of African catfish fingerlings/juveniles being sold. Many African entrepreneurs are attracted to start a hatchery, but only very few succeed. On the long term I personnaly do not believe in small backyard farmers producing some fingerlings but in medium sized operations using recirculation technology well distributed over the country providing people with fingerlings/juveniles of good quality and support people in growing those fish to table sizes fish. What I can see from my experience is that hatcheries in Africa but also in Europe are considered as the centres of knowledge for other farmers.
