Gonadic cycle and environmental modulation of P450 aromatase localization in Cerastoderma glaucum ovary from Monastir Bay

: The gonadic cycle of bivalve molluscs is highly variable and depends on several factors, including the geographical location and environmental conditions of the populations. The aim of this study was to analyse the gonadic cycle of Cerastoderma glaucum female by monitoring a population sampled in Monastir Bay (Tunisia) over a period of 13 months, correlating histological analyses of the ovary with environmental parameters. In addition, we studied the localisation of P450 aromatase, a key enzyme involved in the biosynthesis of 17β-estradiol, to understand its possible role in regulating the oogenesis process. Histological analysis of the ovary revealed the constant presence of oocytes at different stages of maturation, suggesting an asynchronous reproductive cycle, in which the reproductive phase of C. glaucum is continuous throughout the year, without periods of quiescence, and is characterized by three main reproductive events: one in spring, the most significant in summer and a final one in autumn. Environmental factors such as temperature appear to support the progression of gametogenesis, while salinity appears to influence the gamete release phase. Finally, the distribution of aromatase showed a clear correlation with oocyte maturation stages, suggesting a direct involvement of the enzyme in the progression of the female gonadal cycle. Aromatase expression therefore appears to respond to environmental changes, such as variations in water temperature, suggesting a possible mechanism of environmental regulation of reproductive function.