Assessment of the interaction of marine farms and 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 the gonads, gametes (sperm and eggs), and larvae make a considerable contribution to this interaction. Because 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. Among these materials, testosterone, estradiol, fatty acids, as well as some trace minerals such as selenium and zinc are known to affect spawning, growth, and development. The mollusks 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 elements of the budget of steroid hormones, fatty acids, and some biologically important trace elements (Zn and Se) in mussel gonads, gametes and larvae. The total testosterone and estradiol in the gonads and gametes was quantified by enzyme–linked immunosorbent assay. The concentration of the trace elements was found using inductively coupled plasma mass spectrometry. The fatty acid composition was determined by means of gas chromatography–mass spectrometry. The concentrations of selenium and zinc in mussel gonads and gametes were found to depend on the stage of the reproductive cycle. In female gonads, the concentrations of selenium and zinc were higher than in male ones. The highest concentration of selenium was found 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. The concentration of zinc 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 concentration of zinc was, respectively, 53.6 ± 10.9 and 49.3 ± 8.2 μg·g-1 d. w. The mean values of selenium and zinc assimilation degree (q) in gonads of mussels in spring were in the range of 0.1–0.6. The limit values of the alimentary accumulation coefficient (Kp) of selenium and zinc ranged from 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 mollusks 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. Selenium and zinc, when combined with proteins, play a key role in the reproduction and formation of larval shells.