Alphonse Adite

Convergent evolution of weakly electric fishes from floodplain habitats in Africa and South America

An assemblage of seven gymnotiform fishes in Venezuela was compared with an assemblage of six mormyriform fishes in Zambia to test the assumption of convergent evolution in the two groups of very distantly related, weakly electric, noctournal fishes. Both assemblages occur in strongly seasonal floodplain habitats, but the upper Zambezi floodplain in Zambia covers a much larger area. The two assemblages had broad diet overlap but relatively narrow overlap of morphological attributes associated with feeding. The gymnotiform assemblage had greater morphological variation, but mormyriforms had more dietary variation. There was ample evidence of evolutionary convergence based on both morphology and diet, and this was despite the fact that species pairwise morphological similarity and dietary similarity were uncorrelated in this dataset. For the most part, the two groups have diversified in a convergent fashion within the confines of their broader niche as nocturnal invertebrate feeders. Both assemblages contain midwater planktivores, microphagous vegetation-dwellers, macrophagous benthic foragers, and long-snouted benthic probers. The gymnotiform assemblage has one piscivore, a niche not represented in the upper Zambezi mormyriform assemblage, but present in the form of Mormyrops deliciousus in the lower Zambezi and many other regions of Africa.

Trophic ecology and ecomorphology of fish assemblages in coastal lakes of Benin, West Africa

Abstract:The feeding ecology and morphological diversification of fish assemblages of two coastal lakes in southern Benin (West Africa) were examined to compare patterns of community organization. Though located only 18 km apart, the two fish assemblages had dissimilar species composition, and this is largely derived from differences in connectivity to the Gulf of Guinea, salinity and pH. Among the 35 and 20 species sampled from Lake Nokoue (connected with a sea) and Lagoon Toho-Todougba (no sea connection), respectively, only a few species dominated each system. Lake Nokoue was dominated by the perciform Gerres melanopterus and the clupeiform Ethmalosa fimbriata, and Lagoon Toho-Todougba was dominated by the characiform Brycinus longipinnis. In Lake Nokoue, the akadja habitat (dense stands of woody debris installed by humans to attract fishes) had high species richness compared to the other lake habitats. Multivariate procedures were used to examine trophic guilds and the relationship between morphology ...

Ecology and fish catches in natural lakes of Benin, West Africa

SynopsisA preliminary study of the ecology and commercial fish catches was carried out in the Toho-Todougba, Ahouangan and Dati lakes (1500 ha) in southern Benin (West Africa) over a period of 18 consecutive months. Water quality, species richness, and the reproductive biology of the dominant species, Sarotherodon galilaeus, were examined. Unlike Lagoon Toho-Todougba, lakes Ahouangan and Dati are less favourable for fish production because of their high total iron content and their relative low pH. The study revealed the existence of 19 species belonging to eleven (11) families: 16 species in Lagoon Toho-Todougba,12 in Lake Ahouangan, and 7 in Lake Dati. Lakes Ahouangan and Dati had a relatively high faunal similarity whereas Lagoon Toho-Todougba exhibited a relatively low faunal similarity with the former systems. In Lagoon Toho-Todougba, six cichlid species were the most important component of the fishery: Sarotherodon galilaeus, Tilapia guineensis, T. zillii, T. mariae, Chromidotilapia guntheri, Hemichromis fasciatus. Three catfish species Chrysichthys auratus, Clarias agboyiensis, and Clarias lazera were harvested in low abundances. Some other fish, such as Polypterus senegalus senegalus, Protopterus annectens and Heterotis niloticus were captured sporadically, with H. niloticus appearing more consistently in catches than the others. Although not abundant, Gymnarchus niloticus and the African pike, Hepsetus odoe, were almost always present in the catches. Ctenopoma kingsleyae appeared only in Ahouangan. Some predatory species, such as Notopterus afer and Xenomystus nigri, are encountered only in lakes Ahouangan and Dati. In Lagoon Toho-Todougba, Sarotherodon galilaeus had a sex ratio (♂: ♀) of 0.49:1, and size at maturation was estimated as 12.3 cm TL. The spawning period extended from May to September with the peak occurring in July. Fecundity was correlated to log-body length (r = 0.74) and log-body weight (r = 0.76). Fish catches were estimated at 389 kg ha−1 year−1; about 73% of which was Sarotherodon galilaeus. The overexploitation of juvenile fish and the use of this lagoon for the irrigation of palm tree plantations have reduced fish recruitment and mean size.

Genetic differentiation of a primitive teleost, the African bonytongue Heterotis niloticus, among river basins and within a floodplain river system in Benin, West Africa.

Examination of eight microsatellite DNA loci revealed high levels of genetic differentiation among populations of the African bonytongue Heterotis niloticus from three river basins that constitute important fishing areas in Benin. Low levels of population genetic differentiation were detected within the Ouemé-Sô River floodplain system. These results have important implications for conservation and management of stocks supporting important inland fisheries in West Africa.

Growth Performance, Feed Utilization and Body Composition of Clariasgariepinus (Burchell 1822) Fed Marine Fish Viscera-based-diet in Earthen Ponds

A 90-days experiment was conducted to study the effect of replacement of fishmeal (FM) with marine fish viscera (MFV) meal on growth performance, body composition and production of Clarias gariepinus fingerlings (mean weight 11.3 ± 0.1 g). Diets were three isonitrogenous (43% crude protein) and isoenergetic (20 KJ/g) diets containing 0% (D0), 30% (D30) and 50% (D50) of MFV, as FM substitute. Diet D0, without MFV, acted as a control. All these diets were compared to the commercial diet coppens developed for C. gariepinus. No significantly differences were found in final weight (range: 220.94-234.1 g), weight gain (range: 1937.2-1971.7%), specific growth rate (range: 3.30-3.37%/day), protein efficiency ratio (range: 1.93-2.09) and annual production (range: 378.3-415.0 kg/are/year) of fish fed coppens diet, D0 and D30 (p>0.05). Fish fed D50 showed significantly lower growth and feed utilization performances (p˂0.05). Moisture and crude protein were similar among dietary treatments (p>0.05). Lipid deposition in fish significantly increased with MFV level in diets, whereas ash content decreased (p˂0.05). The study indicates that MFV meal can be used up to 30% in formulation fish feed for promotion of Clarias gariepinus rearing in rural areas.