Studies on the biology of two species of catfish Synodontis schall and Synodontis nigrita (Ostariophysi : Mochokidae) from the Oueme River, Benin

The abundance and distribution, length-weight, condition factor, diet and reproduction of Synodontis schall and S. nigrita from the Oueme (Benin) are described. S. nigrita is less abundant than S. schall in the river. Both species are euryphagous with their diet containing a wide variety of food items that include various types of plankton, invertebrates and plants. This high diversity of the food composition indicates a wide adaptability to the habitats in which they live. This is an important strategy for survival and an advantage over the fish species competing for a specific food item. Size at maturity differs between species for both males (15 cm TL for S. schall and 21 cm TL for S. nigrita) and females (16 cm and 22 cm, respectively). Fecundity range is higher for S. schall (1841 15076 oocytes) compared to that of S. nigrita (2647 - 9212). Peak values of GSI for males and females in both species occurred from mid- to late July, indicating one season of major spawning activity per year.