Reproductive aspects of European hake, (Merluccius merluccius, Linnaeus, 1758) based on histological depiction of both sexes in the Eastern Mediterranean (Aegean Sea)

Despite European hake's (Merluccius merluccius) economic and ecological significance, there are still significant gaps in our knowledge. The present study updates some aspects of European hake's reproductive biology and for the first time microscopically showcases all reproductive stages for both sexes from the Aegean Sea (Eastern Mediterranean), which were sampled using commercial bottom trawls between May 2021 and October of 2022. The reproductive cycle of 861 individuals (413 males and 448 females) was assessed, with gonad-somatic index (GSI) exhibiting a seasonal cycle peaking in late spring (May) and attaining lowest values in late summer (August). A highly significant seasonal and sex effect and their interaction on the GSI was further exhibited. The oocyte diameter frequency distribution of the different maturity stages exhibited significant size differences between the juvenile virgin stages (I and II) and adult immature and maturing stages (III, IV and V), due to the presence of cortical alveolar oocytes. Male to female ratio for the entire population was not significantly in favor of females (0.92:1), however sex ratio exhibited a significant male prevalence in smaller sizes (less than 30 cm in total length) and a female prevalence in larger sizes. Females reached the onset of sexual maturity (L50) at higher sizes (38.93 cm) compared to males (29.44 cm) with onset of sexual maturity for both sexes reached at significantly higher length compared to other published Mediterranean studies.

Automated summary

This study provides new insights into the reproductive biology of European hake by analyzing samples from the Aegean Sea. The results show seasonal variations in the reproductive cycle and significant differences in sex ratio and onset of sexual maturity between different size ranges.