The length-weight relationship is a valuable tool for the effective management and utilization of fish stock fauna. For successful restoration and sustainable management of the lower River Niger, it's crucial to have updated data on the length-weight relationship of its fish species, which is currently lacking. This study focuses on the relationship between the length and weight, and the condition factor of the five most abundant fish species found in the lower River Niger, Agenebode in Edo State Nigeria. This study was carried out for 21months using gillnets of different mesh sizes at three zones (lower, middle and upper streams) of the water body. Fish specimen was collected using nets mesh sizes (25.4, 38.1, 50.8, 63.5, 76.2, 88.9, 101.64, 114.3 and 127) mm. Sampling was carried every month to cover for two dry and two wet seasons. The fish specimens were photographed and placed in a box of ice-block to reserve its quality before transportation to the laboratory for identification, measurement and sorting. The biometric data was measured for individual fish to the nearest 0.01cm and 0.01 g, for Standard Length and the Body Weight respectively. The weight-length relationship was determined using the Fulton condition factor. The average of the weights and lengths of the classes were used to analyze the data according to the format compactible with Fisheries Stock Assessment Tool (FISAT II). The degree of association of the length-weight relationship was calculated from linear regression analysis. The exponential equation for the length-weight relationship for each species are: Wt=0.21859(SL)2.7981 for Xenomystus nigri; Wt=0.21859(SL)2.2821 for Synodontis clarias; Wt=-0.031452(SL)2.4364 for Brycinus nurse; Wt=0.0070454(SL)2.3859 for Clarias gariepinus and Wt=-0.011683(SL)2.2821 for Oreochromis niloticus. The five species studied exhibited allometric growth rate at b3, apart from Xenomystus nigri that had isometric growth rate at b = 3.

The value of the condition factor varied from 0.27435 for Clarias. Gariepinus to 3.17215 for Oreochromis niloticus. The combination of the five species and the monthly factors for each of the species studied showed significant difference in the condition factors: Xenomystus nigri (0.76328+0.043), Brycinus nurse (3.125+0.018), Synodontis clarias (0.60939+0.382) Clarias gariepinus (0.27435+0.008) and Oreochromis niloticus (3.17215+0.003).