Food and feeding habit of Mormyrus rume (Valenciennes, 1846) in Lake Geriyo, Adamawa, Nigeria

Mormyrus, a prominent fish within the Mormyridae family in Lake Geriyo and are commercially found in fresh, smoked, fried and roasted forms across the diverse markets of Adamawa, Nigeria. The feeding habit of elephant snout fish from Lake Geriyo was studied during the period of dry season between October, 2022 to March, 2023. A total of 134 samples of fish species were sampled monthly from commercial fishers’ catches at exactly 6:00am at the landing site. The major fishing methods employed by fisher folks for collecting the specimens were cast netting and set netting. The stomach contents were analysed using numerical and frequency of occurrence approaches. The results from this study indicated out of the 134 specimens collected during the study period, 69 were males, and 65 were females. Stomachs of 65 and 64 individuals were found to have recognizable food items. The higher percentage of identified food items by number were benthic insects and detritus which accounted for 69.713% and 64.155% respectively, while the higher percentage frequency of occurrence were detritus and chlorophytes accounted for 100% and 98.462% respectively. This revealed that M. rume is a bottom feeder, since benthic insects and detritus were the dominant food components. Diatoms, crustaceans, rotifers and protozoans had relatively lower contributions. The numerical analysis revealed insectivorous behaviour, the frequency of occurrence indicated detritivorous behaviour, and the relative contribution index demonstrated a preference for insects over detritus. Variation in stomach fullness revealed that 45.522% of the total stomachs examined were at a half-full capacity and females consistently showcase higher foraging intensity than males. The most influential factor affecting the foraging activity of M. rume was the cold phase of the dry season.