COMPARATIVE HISTOLOGY OF TESTES OF BROWN (SALMO TRUTTA M. FARIO) AND CALIFORNIA (ONCORHYNCHUS MYKISS) TROUT DURING THE SPAWNING PERIOD

The testes of fish are paired organs, of a variable shape in different species of fish. Their structure in the salmonid species is lobular. With the histological assays, we established that the lobes were separated by the connective tissue septa, which, given the intensity of spermatogenesis in the studied groups of fish (Salmo trutta m. Fario; Oncorhynchus mykiss) sporadically disappear, in fact, they break. In the space between the lobes there are also cross-sections of blood vessels with visible erythrocytes. During the spermatogenesis, in the interstitium there are clearly observable interstitial endocrine (Leydig) cells that excrete steroid hormones. The intensity of the spermatogenesis in the studied fish varies, which is concluded on the basis of the presence of the spermatogenesis cells. In nature, the reproductive cycle in fish is mostly based on an annual cycle, and that is why different stages of reproduction take place at a different temperature and during a different photoperiod. Hence, regardless of the same time period, the spawning time in November, different types of breeding, and finally salmon farming, point to the very important factors that influence reproduction - diet and microclimatic conditions.