Biological assessment of Oreochromis niloticus (Pisces: Cichlidae; Linne, 1958) in a tropical floodplain river

Biological assessment of Oreochromis niloticus was conducted monthly between January, 2004 and December, 2006 in 3 zones [(Zone I: upper Cross River (savanna wetlands) Zone II: middle Cross River(savanna/forest wetlands) and Zone III: lower Cross River (forest wetlands)] along 200 km length of the inland wetlands of Cross River, Nigeria. Major items in the diet of O. niloticus were algae and plant 38and 20.4% (Zone I), 21.7 and 18.0% (Zone II), 20.2 and 26.9% (Zone III), respectively. Diet breadth ranged from 0.820 - 0.913. Food richness and Gut Repletion Index were 12 and 100%, respectively. Sex ratio was 1: 1 (Zone1), 1:0.78 (Zone II) and 1: 0.89 (Zone III). Mean allometric coefficients (b) of the lengthweight relationship were 2.194 ± 0.215 (Zone I), 2.935 ± 0.333 (Zone II) and 3.03 ± 0.202 (Zone III).Fecundity varied from 70 eggs for fish (total length (TL) = 11.00cm and weight (W) = 37.9 g) to 502 eggs (TL = 25.8cm and W = 198.8g) in Zone I, 60 eggs (TL = 13.3cm and W = 19.8g) to 709 egg (TL = 26.5, W= 317.0) in Zone II and 110 eggs (TL = 13.7cm, W = 24.0g) to 811 eggs (TL = 22.8cm, W = 278.8g) in Zone III. Relationship exists between fecundity and body size. Mean condition index ranged from 0.770 ± 0.128 minimum for males at Zone I to 1.188 ± 0.157 maximum also for males at Zone III. Therefore, male O. niloticus were in better condition than females and the forest wetlands of Cross River (Zone III) offered more favourable living conditions for the species than the savanna wetlands (Zone I and II)