Age and growth of Oreochromis niloticus in the Samandéni Reservoir, Burkina Faso: a scale-based study

Résumé fourni par la source

Oreochromis niloticus is a key species supporting inland fisheries in tropical African reservoirs, including the recently impounded Samandéni Reservoir in Burkina Faso. However, age-based information required for reliable stock assessment remains limited for this reservoir. This study estimated age structure, growth parameters, and population characteristics of O. niloticus using scale readings from 318 specimens collected monthly between October 2021 and September 2022 at three sampling sites: Badoville (n = 114), Sadina (n = 100), and Dioufoulma (n = 104). Monthly sample sizes were relatively uniform, ranging from 25 to 28 individuals, ensuring consistent temporal coverage throughout the study period. Scale annuli were examined and validated using marginal increment analysis. The population exhibited a unimodal length-frequency distribution ranging from 10.0 to 32.0 cm (mean±SD: 20.38±0.17 cm). The sex ratio was significantly male-biased (2.06:1, χ² = 38.04, p < 0.001). Length–weight relationships indicated isometric growth for the pooled population (b = 2.96), negative allometry in males (b = 2.92), and isometric growth in females (b = 3.09). Marginal increment analysis confirmed annual annulus formation, with minimum values occurring in February during the dry season. The von Bertalanffy growth model showed rapid juvenile growth followed by a progressive decline after maturation. Age classes ranged from 0+ to VI+, with dominance of intermediate age groups (II+ to IV+), suggesting continuous recruitment and moderate exploitation pressure. These results provide the first validated scale-based age and growth parameters for O. niloticus in the Samandéni Reservoir and contribute essential baseline information for sustainable fisheries management.