Analysis of fatty acids and sex steroid hormones in rainbow trout testes (Oncorhynchus mykiss) during the reproductive process

In the present study, we aimed to examine the cellular structure of the testes, thehormonal changes occurring throughout the reproductive cycle, and the fatty acidcomposition in rainbow trout. An electron microscopic analysis was conducted to investigatethe morphology and cellular changes during the development of the testes.Germ cells were observed in different stages of differentiation: primary spermatogonia(PSGs), secondary spermatogonia (SSGs), primary spermatocytes (PSCs), secondaryspermatocytes (SSCs), spermatids (SPDs) and spermatozoa (SZs). Differentiatedspermatozoa were observed within the cysts. Regarding steroid hormones, the maximumlevel of testosterone was in the mature stage, and the minimum level was in thespent stage; for 11-ketotestosterone,the highest level was in the maturing stage andthe lowest level was in the spent stage. In terms of the fatty acid composition, thelevels of C14, C15, C16, C18, C16:1n7, C18:1n7, C18:1n9, C20:4n6, n-3PUFAs, n-6PUFAs, C20:5n-3(EPA), C22:5n-3(DPA) and C22:6n3 (DHA) (g-1 of gonad wet weight)were the lowest during the immature stage and the highest during the mature stageof the testes. The major significance of the study is the sex steroid hormonal profile,the primary regulators of spermatogenesis and the fatty acid composition, which isimportant for the development of gonads and sperm. These data should contribute tothe knowledge regarding the reproductive biology of male rainbow trout, for whichresearch data remain scarce.