Condition Factor and Feeding Ecology of Auchenoglanis occidentalis from River Mada, North-Central Nigeria

Abstract

The condition factor and feeding ecology of Auchenoglanis occidentalis were investigated in River Mada, Akwanga Local Government Area, Nasarawa State, Nigeria, using specimens obtained fortnightly from artisanal fishers between November 2020 and October 2021. Length–total weight relationships were derived from log₁₀-transformed total length (TL) and body weight (BW) data for males, females and combined sexes, and Fulton's condition factor (K) was determined monthly. The combined-sex regression equation was log₁₀(BW) = 1.108 + 0.908 log₁₀(TL) (R² = 0.284; b = 0.908), while males (b = 0.823, R² = 0.245) and females (b = 1.027, R² = 0.336) both showed negative allometric growth, indicating that fish increased more in length than in weight. Mean monthly K values ranged from 0.865 to 4.775, peaking in March, May and June, and declining sharply in July, a pattern attributed to reproductive and feeding cycles. Stomach content analysis of 522 specimens (438 with food; vacuity index = 16.09%) revealed a broad, omnivorous diet dominated by worms (IRI = 1425.01), plant material (IRI = 1106.02), insects (IRI = 1010.68) and fish remains (IRI = 971.11), with minor contributions from insect parts, algae, molluscs, mud and sand. Mean gut length and weight were 23.74 ± 0.53 cm and 3.48 ± 0.10 g, respectively, and both increased with increasing stomach fullness. These findings confirm that A. occidentalis in River Mada is an opportunistic, benthic-feeding omnivore that, despite a negative allometric growth pattern, maintains good physiological condition for much of the year, driven largely by feeding intensity and reproductive cycling.