The Couffo basin is not well known, and neither are its aquatic living resources, such as fish fauna, which are subjected to high exploitation rates. The objectives of this study were to establish length-weight ratios (LWRs) and length-length ratios (LLRs) for the most important species in the catches and those of certain economic value. A total of 12,191 specimens belonging to 40 commercial species of actinopterygian fishes were caught with several fishing gears and methods between February 2018 and March 2021. Allometric coefficient b of the LWRs (BW = a × TL b ) ranged from 2.194 for Enteromius callipterus to 3.673 for Protopterus annectens with a mean of 2.902 ± 0.315. The growth of thirteen species was isometric, that of fourteen species was negatively allometric, and that of the remaining thirteen species was positively allometric. Coefficient of determination r2 for the LLRs of 39 of the 40 selected species mentioned above was significant and ranged from 0.781 in Gobionellus occidentalis to 0.997 in Elops senegalensis with a mean value of 0.951 ± 0.049. The results will be useful for further studies on assessments of population dynamics and the sustainable conservation of the already limited fish stocks in the Couffo River basin.