Gonad Development of Black Sea European Flounder, Platichthys flesus, Under Culture Conditions

Diversification of cultured fish species leads to a more resilient aquaculture sector in the face of challenges. The European flounder, Platichthys flesus, is a demersal fish species with great culture potential due to its commercial value. A comprehensive understanding of gonadal development could provide valuable information to understand spawning biology of the species and identify spawning season. Yet detailed information about the gonadal development of the European flounder is not available. In this study, gonadal development and the timing of gonadal differentiation in a Black Sea population of European flounder were investigated by histological examination. Wild European flounder broodstock was captured from the Black Sea before the spawning season and acclimated to culture conditions. Produced offspring were reared in a hatchery for two years in tanks with a seawater flow system at natural water temperature. In July, starting from 15 months of age, five female and five male fish were sampled monthly for a year to assess gonadal development. The hatchery-reared European flounder first reached sexual maturity at around 2 years of age and gonadal development of the testis and ovaries was classified into six successive stages. The gonadosomatic index (GSI) of females increased from July to April and then decreased in May and June while the GSI of males increased from November to January and then decreased in May and June. These results suggest that European flounder in the Black Sea begin to mature in the fall and 2-year-old males and females could be used as broodstock for reproduction in spring under culture conditions.

Automated summary

Diversification of cultured fish species can improve the resilience of aquaculture. This study investigated the gonadal development of the European flounder in the Black Sea and found that they begin to mature in the fall. Two-year-old males and females can be used as broodstock for reproduction in spring.