Diversity and dynamics of fish ovaries: Insights into reproductive strategies, hormonal regulation, and ovarian development

Abstract

Fish ovaries exhibit a remarkable diversity in shape, size, and organization, reflecting the myriad reproductive strategies employed by different species. This review delves into the intricate biology of fish ovaries, highlighting their structural diversity and the hormonal regulation that governs ovarian development and oocyte maturation. Key hormones include pituitary gonadotropins (GTHs) and maturation-inducing hormones (MIHs), which initiate oocyte growth and maturation. GTHs stimulate ovarian production of estradiol-17β and 17α,20β-DP, which induce oocyte maturation via MPF formation. Sex steroids like estrogens and progestogens, synthesized from cholesterol, play crucial roles. Other hormones, including growth hormone, prolactin, thyroid hormones, IGFs, ACTH, and melatonin, influence ovarian activity. The review also explores the varied reproductive strategies among fish, including oviparity and viviparity, and discusses how environmental factors like water temperature and photoperiod influence ovarian histology. Understanding the complex interplay between these factors is essential for advancing fisheries management, conservation, and aquaculture practices. Additionally, the evolutionary trajectory of fish ovaries underscores their adaptation to diverse ecological niches, contributing to the survival and reproductive success of fish species. The ovarian stroma provides structural support and houses various cell types, including dendritic cells (DCs), endocrine cells, and telocytes, contributing to follicle growth and hormone production, essential for reproductive success in fish. Fish ovaries are a crucial aspect of fish biology, with their structure and function intricately regulated by hormonal, environmental, and seasonal factors.