Distribution, abundance, size and feeding habits of Brienomyrus brachyistius (Gill, 1862) (Teleostei: Mormyridae) in a Nigerian rainforest stream

Brienomyrus brachyistius (Gill, 1862) constitutes 64% of the total number of all mormyrid species caught from the upper and middle reaches of Ikpa River in the rainforest zone of south-eastern Nigeria. It inhabits shallow marginal areas and swamp-pools with aquatic macrophytes. B. brachyistius feeds primarily on benthic invertebrates (with chironomid larvae predominating), algae, detritus and secondarily on zooplankton, miscellaneous invertebrates and mud/sans; allochthonous invertebrates and macrophyte material are of incidental importance. The diet varies slightly with growth and season. Feeding activity is higher in the small-sized guild (< 10 cm TL) than large-sized guild (≥ 10 cm TL); it is intense at night but declines during the day and is higher in the dry season than during the rains. Seasonal fluctuations in hydrometeorological regimes (rainfall, water level, flow rate) are critical factors that affect the food and feeding habits of the fish; flood has a depressive influence on food variety and feeding intensity.