Length at first maturity of 42 freshwater fish species in the Itaipu Reservoir reveals strong reproductive-size relationships

The length at first maturity (L50) was estimated for 42 freshwater fish species caught by professional fishers in the Itaipu Reservoir, located in the Paraná River basin, Paraná State, Brazil. Sampling was conducted between March 1988 and October 2024 at 63 professional fishing sites within the reservoir’s area of influence. Estimated L50 values ranged from 8.20 to 81.70 cm. For 19 species, L50 values were reported for the first time. Additionally, updated L50 estimates were provided for 16 species, and new maximum lengths were recorded for 28 species. Statistically clear sex-based differences in L50 were observed in seven species, with males exhibiting higher L50 values than females in five species. Moreover, we recorded strong associations among L50, Lmax, and L100, which provide practical alternatives when reproductive data are limited and support size-based proxies in data-limited contexts. These estimates can support the development of sustainable fishery management strategies and the implementation of minimum mesh-size regulations to help prevent overfishing of commercially targeted species in the Paraná River basin.