Title: Shift in size at first maturity of Nile perch (Lates niloticus) in Lake Victoria.

Nile perch (Lates niloticus) in Lake Victoria plays a critical role as it provides resources for millions of people in Tanzania, Uganda, and Kenya. Concerns about the sustainability of fisheries have emerged because of fluctuations in catch rates and changes in population structure. This study investigates whether the size at which Nile Perch reaches maturity (L50) has changed over the years and whether it is linked to overall stock size. The regional acoustic survey data collected between 2015 and 2022 were analysed using R. The analysis revealed a significant decrease (p < 0.05) in the size at maturity (L50) for Nile perch, with females maturing at a larger size (46.9 cm total length) compared to males (41.6 cm total length). This indicates the potential threats to fishery sustainability and lake ecosystems. Additionally, L50 differed significantly (p < 0.05) between the quadrants of the lake. Areas with a higher estimated biomass had larger L50 values, suggesting a potential link between food competition and maturity patterns. The study also found a larger Nile perch concentrated in the middle and along the coastline, suggesting that these areas provide better growth conditions. The observed decrease in the L50 highlights the need for further research to understand the causes and potential consequences for the fishery and lake ecosystems.