Steroid hormones, selenium, and zinc in the gonads – gametes – larvae biological system of the mussel Mytilus galloprovincialis Lam.

Abstract

Assessment of the interaction of marine farms with the environment in the industrial cultivation of the mussel Mytilus galloprovincialis is very important. In the mussel farm – environment system, biotic fluxes of chemical compounds through gonads, gametes (sperm and eggs), and larvae make a considerable contribution to this interaction. Since gonads play a key role in the mussel reproduction, it is interesting to study the budget of materials, that are directly involved in this process. Out of these materials, testosterone, estradiol, fatty acids, and some trace minerals, such as Se and Zn, are known to affect spawning, growth, and development. The molluscs absorb these materials from food and water. These materials are partly metabolically assimilated by mussels and partly excreted into the environment with gametes. The aim of this study was to estimate the components of the budget of steroid hormones, fatty acids, and two essential trace elements (Zn and Se) in mussel gonads, gametes, and larvae. The total testosterone and estradiol in gonads and gametes were quantified by enzyme-linked immunosorbent assay. The contents of the trace elements were found using inductively coupled plasma mass spectrometry. The fatty acid composition was determined by means of gas chromatography–mass spectrometry. The contents of Se and Zn in mussel gonads and gametes were found to depend on the stage of the reproductive cycle. In female gonads, Se and Zn concentrations were higher than in male ones. The highest concentration of Se was recorded in eggs: (14.7 ± 2.9) μg·g−1 dry weight (d. w.). In sperm, it was (14.4 ± 1.8) μg·g−1 d. w. Zn content in gonads before spawning was higher than in gametes. In male gonads and in sperm, its values were (27.5 ± 3.7) and (19.3 ± 6.4) μg·g−1 d. w., respectively. In female gonads and eggs, the contents of zinc were (53.6 ± 10.9) and (49.3 ± 8.2) μg·g−1 d. w., respectively. In spring, the mean values of Se and Zn assimilation degree (q) in gonads of the mussel were within 0.1–0.6. The limit values of the alimentary accumulation coefficient (Klim) of Se and Zn ranged 0.6 to 1.4. While spawning, mussels excrete polyunsaturated fatty acids (PUFA), which are probably used by other marine organisms. Up to 56.2 % of PUFA are excreted with sperm, and 48.1 %, with eggs, whereas in larvae this fraction does not exceed 10.2 %. The data obtained indicate that the molluscs assimilate sex hormones, fatty acids, selenium, and zinc to maintain vital processes: prostaglandins are synthesized from PUFA in the body, and testosterone esters are formed from testosterone. Se and Zn, when coupled with proteins, play a key role in the reproduction and formation of larval shells.