Temperature effects on the reproductive performance of fish

Introduction Scientists are increasingly being called upon to predict the outcomes of global temperature changes on fish populations. Both reproduction and early development in fish are particularly sensitive to temperature perturbations. Numerous in vitro and in vivo studies have shown that reproductive endocrine homeostasis in fish (Fig. 1) is responsive to changes in temperature. This includes alterations in the secretion and actions of hormones associated with all components of the hypothalamic–pituitary–gonadal axis which controls reproductive processes. By comparison, far fewer studies have considered the longer term consequences of altered temperature profiles on the reproductive cycle or larval development. Even fewer studies have considered the long-term ecological consequences of multigenerational exposures to elevated thermal regimes. Given the existing data and the need for a rapid response to questions on the outcomes of temperature change, our best informed judgement will have to be based, in large part, on information from short-term assays. This leads to the question of whether current methods of assessing the effects of temperature on the molecular and cellular events mediating reproductive processes can be used to predict effects at whole animal and population levels (Fig. 2). This chapter reviews our current understanding of the effects of elevated temperature on reproductive performance in fish. The initial focus is on endocrine homeostasis and the effect of temperature on hormone biosynthesis, metabolism and actions.