Cyclic Variations of Ovarian Development, Hormones and Sex Related Genes of Rainbow Trout (Oncorhynchus mykiss) During Different Growth Stages

Abstract

This study aimed to investigate the reproductive biology of female rainbow trout (Oncorhynchus mykiss). Mature female (n.80) rainbow trout from different reproductive phases were collected. Through a transmission electron microscope (TEM), it was feasible to examine the oocyte at several developmental stages, namely the perinucleolus stage, cortical alveoli stage, vitellogenic stage, mature stage, and postovulatory stage. Progesterone and estradiol levels were measured at their lowest during the immature and spent phases, while reaching their highest levels during the maturing and mature stages. The total amount of saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), and polyunsaturated fatty acids (PUFA) was greater in mature ovaries compared to immature and maturing ovaries. Gene transcripts related to the production of steroids, specifically star, cyp11a1, cyp17a1 and hsd3b were expressed at low levels during the immature stage and showed a significant rise during the mature stage. The ovarian gene expression patterns during oogenesis exhibited distinct dissimilarities. The fatty acid content, essential for the development of fish ovaries, and the sex steroid hormonal profile, which play a key role in regulating oogenesis, are particularly significant. These results will enhance our comprehension of the reproductive biology and sustainable management of rainbow trout in their natural environment.