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Reproductive process in fish is significant physiologically and is of considerable interest, not only for basic research but also for practical application, given the many different species of fish, their key position in vertebrate phylogeny and the increasing importance of aquaculture as a food resource. Seasonal reproduction is governed by endogenous circannual rhythms (biological clocks), which are entrained by various external factors. In facts, fishes correctly integrate environmental cues using specific sensory systems, and then transduce these cues into a cascade of hormones along the entire pineal-brain-pituitary-gonadal axis. 

Disrupting this system, it have recently point out a great number of chemicals pour for the industry that have negative impacts on the reproductive capabilities of multiples water species of vertebrates. Reproductive studies performed mostly in hormonal regulation of reproduction have traditionally been the references for studies in fish reproductive biology. However, the efforts of research scientists around the world have produced significant findings that allow us to identify more elements controlling the full gametogenetic capacity of a mature fish. Interestingly, the gonad is regulated by the hypothalamus-pituitary-gonad (HPG) axis, but it also modulated in an autocrine and paracrine way. This local regulation has recently been pointed out as important for normal gametogenesis and reproductive efficiency. The objective of the present book is to compile the main novel findings that reflect current thinking on fish reproductive biology. 

One chapter is devoted to pituitary as the central endocrine organ in the HPG axis that regulates gonad differentiation. Also two chapters look at different aspect of the HPG axis and revised our knowledge on the hormonal mechanisms that transduce all the environmental cues ensuring that reproduction takes place at the time of year most favourable for the survival of progeny. The public interests in estrogen have been aroused to its actions on male reproduction and a great number of studies have been developed in that sense in mammals and recently in teleosts.

 The role of estrogen in the male reproductive functions is a very novel field of research in teleosts and one chapter of this book revises the role of estrogen in spermatogenesis and spermiogenesis at multiple target sites in hypothalamus-pituitary-testis axis. The studies performed in the recently years have pointed out the great importance of a group of regulatory factors that work in side the gonad and modulate gametogenesis and steroidogenesis. In this sense, a group of chapters review the local regulatory factors of gametogenesis in both testis and ovary. In testis, the novel researches focus on cell to cell interaction inside the gonad that allows the complex regulation of gametogenesis.

Two chapters comply with these studies, one focuses on direct intercellular communication, cell adhesion and the formation of intercellular junctions between germ cells and another one focuses on the regulatory role of the reproductive functions of the immune cells present in the interstitial tissue of the gonad. One chapter looks at to the regulatory mechanism display in the ovary at endocrine and paracrine levels, focussing on proteins and peptides produced in the ovary with local regulatory roles. 

The last chapter that complies with local regulatory mechanism in both testis and ovary introduce us into the recent advances obtained in this field applying genomic approaches. Finally, one chapter brings us up to date on the effects of environmental pollutants in fish reproductive success and subsequent population dynamics. An extended overview of the most important compounds classes that induce endocrine disruption and the present and future approaches to predicting potential endocrine disrupting chemicals is show in this last chapter.