ECOLOGY AND FISH CATCHES IN NATURAL LAKES OF BENIN, WEST-AFRICA

A preliminary study of the ecology and commercial fish catches was car ried out in the Toho-Todougba, Ahouangan and Dati lakes (1500 ha) in s outhern Benin (West Africa) over a period of 18 consecutive months. Wa ter quality, species richness, and the reproductive biology of the dom inant species, Sarotherodon galilaeus, were examined. Unlike Lagoon To ho-Todougba, lakes Ahouangan and Dati are less favourable for fish pro duction because of their high total iron content and their relative lo w pH. The study revealed the existence of 19 species belonging to elev en (11) families: 16 species in Lagoon Toho-Todougba, 12 in Lake Ahoua ngan, and 7 in Lake Dati. Lakes Ahouangan and Dati had a relatively hi gh faunal similarity whereas Lagoon Toho-Todougba exhibited a relative ly low faunal similarity with the former systems. In Lagoon Toho-Todou gba, six cichlid species were the most important component of the fish ery: Sarotherodon galilaeus, Tilapia guineensis, T. zillii, T. mariae, Chromidotilapia guntheri, Hemichromis fasciatus. Three catfish specie s Chrysichthys auratus, Clarias agboyiensis, and Clarias lazera were h arvested in low abundances. Some other fish, such as Polypterus senega lus senegalus, Protopterus annectens and Heterotis niloticus were capt ured sporadically, with H. niloticus appearing more consistently in ca tches than the others. Although not abundant, Gymnarchus niloticus and the African pike, Hepsetus odoe, were almost always present in the ca tches. Ctenopoma kingsleyae appeared only in Ahouangan. Some predatory species, such as Notopterus afer and Xenomystus nigri, are encountere d only in lakes Ahouangan and Dati. In Lagoon Toho-Todougba, Sarothero don galilaeus had a sex ratio (male:female) of 0.49:1, and size at mat uration was estimated as 12.3 cm TL. The spawning period extended from May to September with the peak occurring in July. Fecundity was corre lated to log-body length (r = 0.74) and log-body weight (r = 0.76). Fi sh catches were estimated at 389 kg ha(-1) year(-1); about 73% of whic h was Sarotherodon galilaeus. The overexploitation of juvenile fish an d the use of this lagoon for the irrigation of palm tree plantations h ave reduced fish recruitment and mean size.