This paper reports on sex-related differences in free steroid hormone concentrations including the concentrations of three naturally occurring estrogens (17β-estradiol E2, estrone E1, and estriol E3) and one androgen (testosterone T) in the tissues (gills and gonads) of the blue mussel Mytilus edulis trossulus sampled from the Gulf of Gdańsk (Baltic Sea, Poland). The dissimilarity in steroid concentrations between tissues was particularly evident in the T concentration with a level in gills almost three times higher compared to gonads (on average, 15.38 ng/g w.w. and 5.31 ng/g w.w., respectively, p=0.00008), suggesting its exogenous origin. In general, a tendency towards a skewed steroid profile related to sex, with E2 more abundant for males and T for females, was observed. Female gonads were characterized by a higher level of T than testis (4.61 ng/g w.w. for females and 0.70 ng/g w.w. for males, p=0.0121). At the same time, the level of E2 found in the testis was higher than in the ovary (4.81 ng/g w.w. and 3.86 ng/g w.w., respectively); however, the difference was not statistically significant. As for gills, similar trend with T and E2 being more abundant in males was observed. At the same time, no disturbances in the sex ratio and gametogenesis process were observed which suggests i) efficient deactivation of free forms of steroids, and/or ii) their little or no physiological role.
Keywords: Baltic Sea; Bivalves; Gills and gonads; Mytilus edulis trossulus; Sex; Steroid hormones.
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