Farmed Catfish of Africa

Figure 2: Whole catfish being smoked in Nigeria (left) and smoked catfish fillet for sale in Netherlands (right)

Figure 3: Small smoked catfish for sale by a roadside hawker in Uganda

Nigerian catfish farmers claim that demand exceeds supply and they easily sell everything they produce.  The fillet is large and free of bones, and the Central African market does not object to the red colour of the flesh.  Unfortunately, catfish has proven more difficult to market elsewhere in Africa and across the globe, resulting in lower production levels in these countries (Table 1).

Table 2: Production of catfish (tons in 2015) and farm gate value for non-African countries that farm the species

The value of catfish in the African market is moderate to high at $3.2/kg in Nigeria and $2.2/kg in Uganda (Figure 4), although this pales against the $5.6/kg in Saudi Arabia and $6.96/kg in Bulgaria!

Breeding catfish in captivity starts by preparing the adults under appropriate water quality conditions with a diet that includes plenty of live foods, such as fish, xenopus, earthworms and chicken liver.  This diet will cause the gonads to develop generous quantities of eggs and sperm, ready to be stripped by the farmer at will.  Twelve hours prior to the desired stripping time the female is given a booster injection of Aquaspawn (based on gonadotropin releasing hormone) at a rate of 0.5m?/kg body mass, to mature the eggs in preparation for release from the ovary.  Such injected females are placed alone in cages in tanks with suitable water quality.  At the expected time the farmer inspects the females’ vent for free-flowing eggs, if she is not yet ready she is returned her to her cage for a further hour and then checked again.  Once the females’ eggs flow freely in response to gentle pressure against her belly, she is wrapped in a damp (almost dry) towel that covers her head, and then stripped into a dry plastic bowl by repeatedly applying gentle pressure down the length of her body from behind her pectoral fins to the vent.  The stripping process takes about a minute to complete; continue stripping her gently until she is only releasing small numbers of eggs.  Stop stripping her at this point to avoid damaging her.

The eggs are weighed, two males are killed and some sperm from each added to the eggs.  At this point we add an equal volume of water from the incubation tanks to the spawning bowl and mix the water, eggs and sperm gently for about 30 seconds.  Thereafter the eggs are distributed evenly across a fine net drifting in the incubation tank, keeping them as a single layer.

Catfish eggs should be incubated at 27-28°C and hatch after 24 hours.  At this stage they utilise they yolk sac and hide in the dark corners of the tank.  After a further 36-48 hours they will have absorbed the yolk sac and started moving around the tank purposefully looking for feed.  You can now start feeding them newly hatched brine shrimp larvae, rotifers, sieved daphnia and other small live feeds.  Two days later you can commence with feeding them fine artificial catfish feed.

In many parts of Africa, the catfish hatchery utilises concrete or plastic tanks.  Commercial farmers tend to utilise glass tanks as this allows for careful inspection to ensure they remain clean, and they can be stacked vertically utilising less floor space without hindering the ability of the operator to view and manage the fish.  If the fry are to be hatched in outdoor tanks or ponds (bad idea!), then be sure to sterilise the container and only fill it just prior to adding the eggs or fry in an effort to protect the vulnerable fry from predatory insects and crustaceans.

Figure 4: Concrete tanks such as these in Uganda are not ideal for the hatchery phase but deeper concrete tanks work well for rearing the fish to market size

Catfish grow extremely rapidly and the hatchery fish should attain a mass of 10g after 8 weeks.  During this time they should be kept indoors to exclude predators and to enable the workers to size sort them every week.  Failure to do so results in the faster growing fish, known as shoots, eating their siblings which quickly reduces the number of fish in the tank.

Hatchery phase catfish are initially extremely fragile and a mortality rate of 75% in the hatchery is normal.  Given that each female provides around 50 000 eggs per kilogram of body mass, and does so every 2 months, catfish are extreme prolific breeders.  Once the fish attain 10g they are very tough and can be moved from the small hatchery tanks into larger tanks or even earth ponds.  Tanks work well for catfish as they can be stocked to attain super high densities exceeding 500kg/m3 at harvest, and grow well under these conditions provided that the water quality remains good.  In earth ponds they are stocked at far lower densities, and they are more difficult to manage, so earth ponds are not well suited to commercial catfish farming.  Cage culture does work for catfish in tropical areas but has not yet become very popular.  Between 10g and the market size catfish should be sorted twice again to remove shooters and keep similar sized fish together.  The primary responsibility of the farmer during the growout stage is to ensure the fish receive adequate and appropriate feed, that the water quality remains optimal and that the density is correct.  Meet these simple requirements and your catfish should grow extremely fast from 10g to 1kg in 4 months.

Figure 5: Catfish fry (left) and fingerlings (right) in hatchery tanks

In tropical Africa catfish are often stocked into tanks that have no water flow, but the total volume is replaced daily.  Provided that the density is modest and the fish waste does not overwhelm the fish prior to the next water change, this method is effective with a low investment cost and low risk option.  Larger scale commercial producers utilise recirculating systems to hold catfish at super-high densities and maintain good water quality whilst the fish are being fed a diet for maximum growth.  Such systems can produce 20 tons of fish p.m. from a mere 400m2.  Naturally these systems require a substantial capital investment and do have a higher risk than the low-density systems.

Figure 6: Earth ponds being used to farm catfish in Uganda, such systems are not very productive and complicate the regular management these fish require

Figure 7: Concrete tanks being used for farming catfish inside a greenhouse tunnel in South Africa; such commercial systems are highly efficient in terms of water and space usage, and enables the exclusion of diseases and predators

Some catfish farmers make their own feeds based on locally available ingredients but as the industry matures most growers, and certainly the commercial farmers, utilise commercial feeds formulated for optimal growth of the catfish and minimal wastage.  Live feeds are always beneficial, especially for the hatchery and breeders.

Catfish fry are sensitive to various pathogens and parasites but as they grow they become robust towards these pests.  As such, hatcheries rely on ultra violet sterilisers to control bacterial proliferation but growout systems do not utilise sterilisation.

Catfish are fast growing, produce huge quantities of eggs, can breathe atmospheric air and are tolerant of adverse water quality.  This enables them to be farmed at a lower cost than any other fish species, making North African Catfish one of the worlds’ ultimate aquaculture species.  The popularity of the species as an eating fish is also growing and the future of the farmed catfish of Africa looks very bright.

References: 
All production statistics were sourced from:
http://www.fao.org/fishery/statistics/global-aquaculture-production/en