Testosterone concentration and aromatisation efficiency at different stages of gonad development: a case study with Mytilus edulis trossulus.

Sex steroid hormones occur in the bivalve tissues. Testosterone (T), various oestrogens, and progesterone have been reported in this group of organisms and the amounts of these hormones have been correlated with seasonal variation and reproduction. Yet, neither the role nor the origins of sex steroids are fully clarified. Thus, we tested the hypothesis that, apart from the esterification process, the aromatisation of androgens to oestrogens can help balance T levels during gonadal development in both sexes using Mytilus edulis trossulus as a model species. The highest testosterone concentrations were found in developed male and female gonads (IV reproductive stage of gametogenesis). The highest aromatisation efficiency was also found in the developed male and female gonads, but also in the gills. During the other stages of gametogenesis (II, III, V-I), a decrease in both testosterone concentration and aromatisation efficiency was observed in the gonads of males and females, as well as in the gills of males. However, the decrease in testosterone concentration did not affect the 17β-oestradiol concentration in mussel tissues. Thus, together with the esterification process, the ongoing aromatisation in bivalve tissues may help keeping balanced T levels. [ABSTRACT FROM AUTHOR]