Growth Allometry and Condition Factor of Some Mormyrids in Lower River Niger at Idah, Kogi State, Central Nigeria

The study examined the growth allometry and condition factor of six Mormyrids of lower River Niger at Idah, Kogi State of central Nigeria. Three hundred and thirty two (332) mormyrids namely Mormyrus rume, Mormyrus macrophthalmus, Mormyrops deliciosus, Hyperopisus bebe occidentalis, Gnathonemus petersii and Pollimyrus isidori were obtained monthly from the local fishermen between June 2024 and November 2024.The fish were caught using 5.1 cm and 7.3 cm gill nets as well as traditional valved basket traps. The collected specimens were transported in ice-packed plastic containers to maintain freshness. Species identification was carried out in the laboratory using established taxonomic references. Standard length and body weight of the specimens were measured to the nearest 0.1cm and 0.1g respectively. The length-weight relationship (LWR) was determined using the equation W = aLb, while condition factor was evaluated using the equation K = 100 × W/L3. Results revealed variations in LWR among species with M rume and P. isidori exhibiting positive allometric growth having b value of 3.1 and 3.2 respectively, M. macrophthalmus and G. petersii showed isometric growth (b = 3) while M. deliciosus and H. bebe occidentalis displayed negative allometry of 2.9 and 2.7 respectively. The condition factor analysis revealed significant differences (P < 0.05) among the species. G. petersii exhibited the highest condition factor (1.67) while M. deliciosus had the lowest (0.72). The findings highlighted the need for targeted conservation strategies to protect critical habitats and maintain resource availability, particularly for species with lower condition factors. Mitigating environmental stressors such as pollution and habitat degradation are essential for sustaining the health and growth potential of Mormyrid species in the lower River Niger. Long-term monitoring programs are recommended to assess population trends, growth dynamics, and environmental influences, ensuring adaptive management strategies that promote the sustainability of these ecologically significant fish species.