Reproductive Biology of Male European Hake (Merluccius merluccius) in Central Mediterranean Sea: An Overview from Macroscopic to Molecular Investigation

The improvement of scientific knowledge about overexploited fishery resources allow us toprovide scientific advice for their management and stock protection. By using a multidisciplinaryapproach, the aim of the study was to characterize, for the first time in the Central Mediterranean Sea(GSA 17), the reproductive biology of males of M. merluccius, currently highly exploited. A multi-yearsampling from January 2017 to December 2019 was performed to exhaustively evaluate the sex ratioof the stock, while the 2018 annual sampling was selected to investigate the reproductive patternof males. Individuals in spawning conditions were found every month, proving that M. merlucciusis an asynchronous species, reproducing all year round, with a seasonal reproductive peak inspring/summer, as indicated by GSI. Five gonadal development stages were defined to fully describethe reproductive cycle of males. The macroscopic and histological L50, respectively 18.6 cm and15.4 cm, were both below the Minimum Conservation Reference Size (MCRS). According to themRNA levels, fsh and lh played a significant role during spermiation, whereas the gnrhr2a wasinvolved at the beginning of sexual maturity. In the testis, fshr and lhr reached maximum expressionlevels before the spermiation. The hormonal stimuli of 11-ketotestosterone and its receptor weresignificantly higher when the specimen was in reproductive activity