By Professor Ross G. Cooper
Formerly: Department of Physiology, University of Zimbabwe, Harare, Zimbabwe.
There are 23 species of catfish in Zimbabwe. They are carnivorous and scavenging fish characterised by scaleless bodies and conspicuous feelers or barbels around the mouth. They range in size from the spotted catlet and rock catlets, barely reaching 6cm to the vundu (Heterobranchus longifilis) weighing 50kg or more. They have good aquaculture potential in commercial fishponds. The airbreathing catfish (family Clariidae) have additional breathing organs (spongy structures above the gills) which allow them to breathe atmospheric air, permitting them to survive in stagnant water and out of water for a long time. They have a uniform dark brown dorsal surface extending down over the flanks almost onto the white throat and belly. They have broad flat heads, small eyes, four pairs of well-developed sensory barbels, a small swim bladder and long dorsal and anal fins. The sharp tooth catfish is the most common fish in Zimbabwe and the only fish found in all ten recognised river systems. Exceptionally large specimens reach 30kg (Zimbabwean National Angling Record: 30.84kg, D.F. Marsberg, 1947, Middle Zambezi River), making it the second-largest fish in the country after vundu. They are hooked on spoons, and on baits including bird entrails, blue-mottled soap and meat. The fish will also strike at fishing flies! It is a popular angling fish, difficult to land because of its habit of holing up or using the river current to assist it. It has much longer whiskers than other airbreathing catfish and there is a large adipose fin between the dorsal fin and tail. Their diet consists of aquatic food, terrestrial organisms like insects and birds, and offal.
They will consume fish and other prey like snakes, frogs, juvenile crocodiles, snails, shrimps, aquatic larvae and insects, terrestrial insects, grain seeds, fruit berries (especially Syzigum trees), juvenile and adult birds. They often congregate under heronries and consume chicks that fall out of nests. In rapids, the fish is a powerful and fast swimmer, although it is more a stalker of prey than an active predator. They hunt in packs, often encircling fish and chasing them into the shallows where they are swallowed whole. They also congregate in large shoals where floodplains drain back into main rivers after the rainy season. Therein they lie in wait in deeper water and virtually scoop up the shoals of small fish and juveniles of the larger species as they leave the shallow water. Breeding takes place during the rainy season when shoals of ripe fish move out into shallow flooded grasslands to spawn and up 500,000 eggs are laid by each female often commencing during or soon after a heavy downpour. Once laid, the adults move quickly back into deeper water. The eggs hatch in ca.36hr. and the fry tends to remain in the grassy flooded areas, relatively safe from the large fish predators, until falling water levels force them back into the main river. Adults are often trapped in isolated pools in floodplains and non-perennial rivers and have been observed living in mud. There is no evidence that they can aestivate, although the exposed fish provide food for hungry predators and birds. Once the rains start, this fish begins extensive migrations and will colonize newly inundated vleis and watercourses, drainage ditches and the pans which have died out the previous winter.
Figure 1 Adult African catfish (Clarias gariepinus) ca. 85cm long Figure 2 Young Clarias specimens with spotted skin ca. 15cm long
The African sharp-toothed catfish, Clarias gariepinus, is a common fresh-water fish with large barbels found in many river systems in Zimbabwe (Fig. 1), and the young have spotted skin (Fig. 2). The literature includes a number of ecological studies of this fish, although these have not been adequately extended to investigations of its physiological adaptation to food intake and metabolism. C. gariepinus is unique in that it contains two embedded lateral liver lobes in its musculature connected via bile ductules and blood vessels to the main liver lobe in the body. A new avenue in the ecological adaptations of organ metabolism of this fish could be explored by considering possible functional differences between its lobes. The fish can be farmed in large commercial fish ponds, harvested and sold to the local market. From an angling perspective, knowledge of the storage capacity of the liver might be useful indirectly for determining the best waterways to catch the fish given their associations with food intake. Additionally, the embedded lobes consumed with the meat may pose a significant health hazard due to the possible accumulation of environmental toxins, heavy metals and pollutants therein. However, if these lobes together with the main liver are carefully removed and discarded with the other entrails, the meat will if thoroughly cooked in order to destroy helminth parasites, be very nutritious. Indeed, the fish is commonly filleted and the meat marinated in a salt, pepper, herb and vinegar mix overnight before being grilled in an oven or over an open fire. The meat adorned with gravy and fresh lemon juice is delicious and well-eaten with vegetables and rice or sadza.
Professor B.E. Marshall, Dr. P. Lund and Mr. L. Dube formerly of the Department of Biological Sciences, University of Zimbabwe provided advice.
Barson, M. Mabika, N., Cooper, R.G. and Nhiwatiwa, T. 2014. Histopathology and helminth parasites of African catfish Clarias gariepinus (Burchell, 1822) in relation to heavy metal pollution in a subtropical river system. Journal of Applied Ichthyology 30: 923-929.
Bell-Cross. G. and Minshull, J.L. 1988. The Fishes of Zimbabwe. Bulawayo: The National Museums and Monuments of Zimbabwe. pp. 294.
Cooper, R.G. 1993. A histological and ultra-structural investigation of the liver and its embedded lobes in the African catfish Clarias gariepinus (Burchell – 1822). B.Sc. (Hon.) Degree, Department of Biological Sciences, University of Zimbabwe, Zimbabwe. pp. 69.
Cooper, R.G. 2004 A histological and ultra-structural investigation of the liver and its embedded lobes in the African catfish Clarias gariepinus (Burchell – 1822). Discovery and Innovation 16(1&2): 41-46.
Cooper, R.G. 2007. Healthy meat eating? Poster – Proceedings of the 3rd Annual Faculty Research Conference, Sharing Research: a Faculty wide perspective, November 23rd, Birmingham City University, UK: 45.
Cooper, R.G. 2008. Are freshwater fish safe to eat? Indian Journal of Physiology and Pharmacology 52(2): 209-210.
Cooper, R.G. 2008. Eating the African Catfish (Clarias gariepinus). Museum News Oct: 6.
Cooper, R.G. 2010. Clarence the Catfish. ISBN: 978-0-557-30913-9. Morrisville, N.C.: Lulu Press Inc.. pp. 31.
Cooper, R.G. 2011. Eating the African Catfish (Clarias gariepinus). African Fisherman Magazine 22(2): 27.
Cooper, R.G. and Tennett, A. 2008. Transient observations of wildlife along a tributary of the Gwebi River, Mount Pleasant, Harare, Zimbabwe. Zimbabwe Wildlife Journal Oct: 4-5.
Donnelly, B.G. 1973. Aspects of behaviour in the catfish, Clarias gariepinus (Pisces: Clariidae), during periods of habitat desiccation. Arnoldia Rhodesia 6(9): 1-8.
Nhiwatiwa, T., Barson, M., Harrison, A.P., Utete, B. and Cooper, R.G. 2011. Metal concentrations in water, sediment and African sharptooth catfish, Clarias gariepinus, from three peri-urban rivers in the upper Manyame catchment, Zimbabwe. African Journal of Aquatic Science 36(3): 243-252.
Tabex Encyclopedia Zimbabwe. 1987. Harare: Quest Publishing. pp. 431.