First record on size at sexual maturity and optimum catchable length of 10 marine fishes from the Bay of Bengal (Bangladesh) through multi-models approach: a key for sound fisheries management

Appropriate management systems for the protection of fishes are mostly relying on the information of size at sexual maturity and optimum catchable length. The purpose of this research was to estimate the size at sexual maturity (Lₘ) and optimum catchable length (Lₒₚₜ) of 10 marine fish species from the Bay of Bengal (Bangladesh) through multi-models using commercial catches from October 2019 to September 2020. Also, we calculated the Lₘ and Lₒₚₜ of these species from worldwide water bodies based on maximum length (Lₘₐₓ). A total of 2967 specimens of 10 fish species were evaluated in the current study and total length (TL) was noted up to 0.1 cm using a measuring board, while body weight (BW) and gonad weight (GW) are weighed by digital electronic balance with 0.01 g accuracy. To assess the Lₘ, three different models such as (i) empirical model based on Lₘₐₓ, (ii) the relationship between TL (total length in cm) vs. GSI (gonadosomatic index in %), and (iii) logistic model were considered and Lₒₚₜ was assessed based on L∞. The estimated lowest Lₘ was 11.8 cm (Lₘₐₓ-based), 12.8 cm (TL vs. GSI), and 13.7 cm (logistic model) for Thryssa setirostris and highest Lₘ was 23.3, 20.5, and 22.0 cm for Priacanthus macracanthus through Lₘₐₓ, TL vs. GSI, and logistic-based models, respectively. From these three models, the lowest mean value of Lₘ was obtained for T. setirostris (12.7 cm) and highest was recorded for P. macracanthus (21.9 cm). Fifty percent of mature marine species was in 14.9 cm TL and 90% species was in 19.5 cm TL. The smallest Lₒₚₜ was obtained as 13.4 cm TL for T. setirostris and largest was 28.2 cm TL for P. macracanthus. This study was generated data on Lₘ and Lₒₚₜ for 10 newly marine species, which are globally absent. Therefore, this study will be helpful for developing sustainable management strategies and conservation of marine fishes through the implementation of mesh size based on the size at sexual maturity (Lₘ) and optimum catchable length (Lₒₚₜ).