The biology of Parachanna obscura (Osteichthyes: Channidae) in Anambra River, Nigeria

Abstract

The biology of a commercially important teleost, Parachanna obscura was studied for a period of twelve months. Monthly samples of the species were randomly collected from fishermen in the lower reaches of Anambra River, Southeastern Nigeria for the twelve months. The haematological profile established were mean haematocrit of 22.5%, mean blood haemoglobin concentration of 7.23 g/dl, mean red blood cell sedimentation rate 31.25 µm, mean red blood cell count 3.72 (106/L), white blood cell count 2.81×104/L, mean cell volume 60.75 µm3 and mean corpuscular haemoglobin 19.5 pg. The blood groups are O+(10%), O- (90%), genotype AA (88%) and AS (12%). Digestive enzymes assays in the different gut regions of P. obscura revealed an array of glycosidase, proteases and lipases. The pattern of distribution and relative activity of the enzymes is consistent with its predatory diet. Total length (TL) ranged from 23.4 to 28.5 cm and weight from 86.0 to 140 g; males were not longer or heavier than females. Maturity occurred earlier in males than females; 50% of both sexes matured at 24.7 cm TL. Fecundity ranged from 126 to 1580 oocytes (mean 896 ± 477 oocytes). Total length was a better predictor of fecundity than ovary weight. Index of food significance (IFS) showed that insect (51.67%) was the dominant food group, followed by fish (15.66%) and frog eggs (8.02%). Food items of primary importance were ephemeroptera nymphs, chiromomidae, unidentified insects and fishes. Key words: Anambra River, Parachanna obscura, digestive enzymes, haematological profile, blood groups.