Chapter 3.2.4 - EDCs: Focus on male fish reproductive alterations

Abstract

Reproductive disorders related to exposure to environmental contaminants are increasingly diagnosed in human and wildlife alike. Many of these conditions can be attributed to endocrine disrupting chemicals (EDCs), i.e., chemicals whose molecular mechanism of action involves disruption of hormone synthesis, distribution, transport, metabolism and/or action. Hundreds of natural or man-made chemicals fit these criteria and are known or suspected to interfere with physiological and endocrinological regulation of the development and function of reproductive organs. Among EDCs, plasticizers, metals, pharmaceuticals, insecticides, and alkylphenols have drawn special attention due to their adverse effects, such as changes in the development of embryos and fetuses; hormonal level changes, neurotoxicity, fertility decline, genotoxicity, among others. In this chapter we review some of the evidence supporting these chemicals as disruptive of the male reproductive axis in fish. Male fish share the same regulatory components of the reproductive axis as all vertebrates. Neurosecretory neurons in the hypothalamus, mainly GnRH neurons, regulate the release of gonadotropin hormones (GTHs)—follicle stimulating hormone (FSH) and luteinizing hormone (LH)—from the pituitary gland, which in turn control gonadal development, gametogenesis, and steroidogenesis. All chemicals reviewed showed some potential as endocrine disruptors of the reproductive axis in male fish. Selected metals, pesticides, and pharmaceuticals showed potential endocrine disruption at all levels of the axis. The effects of bisphenols and ivermectin are predominant at the testes level, affecting both spermatogenesis and steroidogenesis. It is essential to focus on reducing the impact of these contaminants in the aquatic environment, establishing clear policies and action plans for their use worldwide.