The study evaluated some population parameters of Sarotherodon melanotheron melanotheron within a lagoon complex in southern Benin: Lake Nokoué and Porto-Novo Lagoon. Data on the total length, total weight, and sex were recorded monthly between January and December 2015 for 1,745 specimens captured by local fishermen. The asymptotic length L∞ was estimated at 24.68 cm. The growth rate K was 0.86. The total, natural, and fishing mortalities were estimated at 2.46, 1.71, and 0.75 y−1, respectively. The size at first sexual maturity was 8.9 and 9.2 cm, respectively, for males andfemales. The size at first capture was estimated at 9.2 cm, which indicates that fish spawn at least once before capture. The current exploitation rate of 0.31 remains below the maximum exploitation rate Emax which was 0.604 but was equal to the exploitation rate retaining 50% of the biomass of the stock (E0.5 = 0.324). This suggests that the stock of S. m. melanotheron is not overexploited in the complex. However, it is recommended that the actual rate of exploitation be kept as it is to ensure a sustainable management of these fish populations.

The length–weight relationships (LWRs) and length–length relationships (LLRs) are presented for 18 commercial actinopterygian fish species found in Lake Nokoué and the Porto‐Novo Lagoon. The fish were collected monthly from fishermen from June 2015 to May 2016. The sample size, length range, weight range, LWRs, LLRs, 95% confidence intervals of b, coefficient of correlation r2 and growth type are given for each species. Values of b were between 2.495 (Elops lacerta) and 3.235 (Polydactylus quadrifilis), and r2 values between 0.884 (Elops lacerta) and 0.999 (Acanthurus moroviae). The present study introduces what will serve as the first references regarding LWRs and LLRs for two species (Eleotris vittata and Lutjanus goreensis) in Lake Nokoué and the Porto‐Novo Lagoon. These results will be very useful for future investigations pertaining to population assessment and sustainable conservation practices for the fish stocks in both study areas.

There is a lack of information on many biological and ecological aspects of the critically endangered European eel during its growth phase in inland waters, such as when the sedentary life stage begins, mobility according to age and response to habitat alteration. We used mobile radio frequency identification (RFID) telemetry technology to track tagged eels over 6 years after their restocking as glass eels in six typologically different rivers. We also cross-referenced telemetry data with those of several electrofishing monitoring sessions to better understand the mobility and behaviour of eels. The relative abundance (maximum 52 individuals km−1) and detection rate (maximum 28%) of eels were not significantly correlated with the time/age after restocking. Eels were present in all restocked rivers, but their abundance was low and mobility was high in a slightly acidified, oligotrophic river that had experienced a great loss of fish habitat heterogeneity. This loss of habitat heterogeneity was due to flooding events and machinery works in riverbeds to restore the altered riverbanks. Four years after glass eel release, restocked eels became sedentary and moved from shallow to deep microhabitats with riverbeds dominated by blocks as the bottom substrate. After this age, they exhibited high fidelity to the residence site. This study provides new insights concerning the biology and ecology of eels restocked as glass eels in freshwaters, which should lead to improved management plans for the species through the implementation of more effective conservation measures and strategies.