Sex steroid hormones and steroid secretory cells in the gonads of cyclostomes and fish

. The purpose of this work is to generalize data on the content of sex steroid hormones in cyclostomes and fish in connection with the different state of the gonads, as well as on the localization and ultrastructural organization of steroid secretory cells (SCs). Method used : generalization of literature data. Novelty : for the first time, data on the development of SC in the gonads of juvenile fish are presented on the scale of a literature review; changes in their localization and functional activity are shown. Results : Most of the data on the steroidogenic function of the gonads in fish were obtained in connection with the study of sex differentiation (inversion) and sexual maturation (spawning). The issues of the synthesis of sex steroid hormones and their molecular structure, blood levels in various states of the gonads, as well as the localization and ultrastructural organization of SCs are considered. It has been noted that SCs appear in the gonads long before sex differentiation and can be present among stromal, granulosa, and theca cells. In cyclostomes and fish — juvenile protogynous hermaphrodites in the gonads of genetic males, SCs do not appear in the membranes around the oocytes of the previtellogenesis period, which determines their deficiency of estrogen hormones and, as a result, sex inversion. With induced sex reversal, the development of the steroidogenic function of the gonads proceeds in the opposite direction to its natural development: in males, oocytes appear and steroid activity shifts from the stroma of the gonads into granulosa and theca; in females, on the contrary, secretory activity in the follicular membranes decreases and increases in the stroma of the gonads. Practical significance : the results of the analysis will give insight into the nature of sex steroid hormones, their dynamics in the blood, and their role in the implementation of various processes of gonadogenesis and gametogenesis before their practical use in fish farms.