The Biology Of The West African Clariid, <i>Clarias macromystax</i> Gunther, 1864 (Osteichthyes: Clariidae) In A Nigerian River Basin

The biology of the West African clariid, Clarias macromystax, was studied in Anambra river basin, Nigeria.  The clariid occurred more abundantly and frequently in forest floodplain ponds than in other habitats, and was totally absent in the river systems.  Length ranged from 9.7 to 30.2 cm TL and weight from 9 to 168 g; females were heavier, but not longer, than males.  The b-values (2.4190-2.5209) of the total length-weight relationships exhibited negative allometric function.  Mean relative condition, K n , was better in females than males but showed a definite cycle in both sexes.  Over 50% of both sexes were mature at 15.1-20.0 cm TL in their first year of life.  Fecundity ranged from 2.136 x 10 3 to 37.250 x 10 3 (mean 14.942 x 10 3 ± 11.248 x 10 3 ) and correlated highly and positively with length, body weight and ovary weight.  Ovary weight was the best predictor of fecundity.  Communal spawning involving C. macromystax and C. agboyiensis occurred.  Feeding was carried out throughout the day with higher feeding intensity at night.  Food of primary importance were Caridina niloticus, Sudanonautes africanus, Odonata naiad, terrestrial Orthoptera, formicoid Hymenoptera, Dytiscidae, Oreochromis niloticus, Parachanna obscura, fruits and seeds, plant detritus and mud.  Diet breadth was season-dependent.  The clariid fed by foraging, shoveling and surface feeding.  E. clarias, Procamallanus laevichonchus and a larval spiruroid parasitized various organs.  C. macromystax is a new host record for these helminth parasites.