Reproductive and feeding biology of the Nile tilapia, Oreochromis niloticus (Linnaeus, 1758) (Pisces: Cichlidae) in Lake Tinishu Abaya, Ethiopia

다국어 초록 (Multilingual Abstract)

Understanding the reproductive dynamics and feeding ecology of commercially important fish species is vital for developing effective fisheries management strategies. This is particularly important in African freshwater systems where overfishing and environmental degradation resulting in significant threats to aquatic biodiversity and food security. Here, we investigated the reproductive biology and trophic ecology of Oreochromis niloticus in Lake Tinishu Abaya, Ethiopia, during 2023–2024. A total of 648 specimens were collected from four selected sites using multi-mesh gillnets to ensure representative sampling across different habitats and size classes. The structure analysis revealed a pronounced male-biased sex ratio of 1:0.43 (M:F), which deviated significantly from the theoretical 1:1 ratio (χ2 = 101.14, p < 0.001), indicating potential demographic imbalances within the population.
Moreover, the sexual maturity analysis using logistic regression modeling determined that males attained first sexual maturity at a smaller size (Lm ~50~ = 15.9 cm TL) compared to females (Lm ~50~ = 16.7 cm TL), representing an interspecific difference of approximately 0.8 cm in total length. Likewise, the reproductive activity showed continuous year-round spawning with distinct seasonal peaks, as evidenced by the consistent presence of ripe gonads throughout the sampling period, though the highest reproductive intensity occurred during from January to May for both sexes. The fecundity analysis of 41 gravid females indicated a mean absolute fecundity of 353.63 ± 97.37 eggs per individual, with strong positive correlations observed between egg production and total length (R2 = 0.90) and body weight (R2 = 0.88). Seasonal variations in diet composition were evident, with phytoplankton dominance during the dry season (60.09%) and increased contributions of detritus and macrophytes during the wet season. Based on these findings, we recommend implementing size-based harvest regulations prohibiting the capture of individuals below 16.7 cm TL, establishing seasonal fishing closures during peak reproductive periods (January–May), and creating riparian buffer zones to protect critical feeding habitats, thereby ensuring the long-term sustainability of this economically important fishery resource in Lake Tinishu Abaya.