Some aspects of the reproductive biology of tilapia black-chinned, Sarotherodon melanotheron (Rüppel, 1852) in relation to macrophyte abundance in three marginal lagoons, Southeast of Côte d'Ivoire

Sarotherodon melanotheron is a cichlid species found in abundance in most of estuaries and lagoons of West African. In recent decades, these fish are facing problems with pollution, wetland degradation, macrophyte proliferation and fishing pressure. This study examined some aspects of its reproductive biology and the possible influence of macrophyte proliferation on the reproductive parameters. A total of 1054 fish were collected monthly with cast nets, gillnets, traps, harpoons and hawks between 2017 and 2019. The temperature, transparency, pH, total dissolved solids (TDS), conductivity and dissolved oxygen (DO) were recorded in situ. Water samples were taken, stored in polyethylene bottles (500 mL) and kept at a temperature below 4°C for further determination of nutrients (ammonium-nitrogen NH4+, nitrate NO3−, nitrite NO2− and phosphate PO43−). The overall sex ratio was in favour of males in all lagoons. The length at first sexual maturity (L50) was approximately equal between males and females from the same lagoon. However, it increased as the macrophyte abundance decreased from Ono to Hebe lagoons. The spawning activity started in dry season and became intense in rainy season in Ono and Kodjoboue lagoons or at the end of the dry season in Hebe lagoon. The presence of females with ripe gonads throughout the year gives evidence of multiple spawning and attested that this species reproduces in all seasons. The absolute fecundity was higher in Ono lagoon, indicating a better food supply due to the high abundance of macrophytes.