The impact of parasites, infections and diseases on the development of aquaculture in sub-Saharan Africa

Abstract

Total African aquaculture production in 1994 amounted to 76 660 metric tonnes (t). Of this, 53.8% (41 211 t) was produced by five countries bordering the Mediterranean, while the remainder (35 449 t or 46.2%) was produced by 30 sub-Saharan countries. These figures highlight the low-level intensity of aquaculture in sub-Saharan Africa. A comprehensive literature search was undertaken to gauge the extent of disease and pathogenic agents in fish and shellfish aquaculture in Africa south of the Sahara. The study revealed that bacterial infections as well as parasitic ectoprotozoans, cestodes, trematodes, nematodes, polychaetes and crustaceans are the most prevalent problems in African freshwater, brackish water and marine aquaculture. There have been isolated reports of viral diseases (infectious pancreatic necrosis (IPN), lymphocystis and spring viraema). Bacterial diseases are restricted to common agents such as Aeromonas, myxobacteria and some other ubiquitous facultative bacteria. Saprolegnia is the most common problematic fungus affecting fish under culture conditions. Currently the most widely used chemicals for prophylaxis and treatment include wide spectrum antibiotic formulations, malachite green, methylene blue, formalin, copper sulphate, salt, and several organ-ophosphates. From an aquaculture perspective it was noteworthy that disease and parasite infestation have been poorly studied in Africa as a whole and in sub-Saharan Africa in particular (South Africa being the exception). It is hypothesized that this is mainly due to the low-level intensity of aquaculture in the region. At present the paucity of research on fish diseases in Africa is not seen as a factor that will negatively impact on aquaculture development and as such is not a target research area. Africa is considered to be the sleeping giant of aquaculture and at the present moment it is relatively disease free. It is vitally important that African countries take steps to safeguard this status. One method of accomplishing this is to restrict the importation of fishes into Africa. The importation of ornamental aquarium fish as well as hybrid and genetically improved fish strains pose the greatest threats. The smorgasbord of fish and shellfish parasites and diseases that occur in Israel, for example, can to a large extent be ascribed to uncontrolled translocations. Every effort needs to be made to prevent a similar occurrence in Africa.