A Review on Environmental Contaminants-Related Fertility Threat in Male Fishes: Effects and Possible Mechanisms of Action Learned from Wildlife and Laboratory Studies

Simple Summary:Public concern regarding environmental contaminants (ECs)-related reproductivedisorders has increased due to increasing global rates of infertility. All kinds of ECs are on riserapidly in developing and industrializing low- and middle-income countries. The aquatic envi-ronments throughout the world are repositories for enormous amounts of ECs. As the biology ofthe reproductive system is highly conserved in vertebrates, wildlife or laboratory studies on fishprovide significant information to establish a detailed risk assessment, and to identify novel or moresensitive endpoints for ECs-related reproductive disorders. The adverse effects of ECs on endocrineregulation of reproduction in male fishes have been extensively studied and reviewed; however,our knowledge on the effects and mechanisms of action of ECs on determinants of male fertility islimited. The present study is a state-of-the-art comprehensive review on the ECs-related fertilitythreat in male fishes with emphasis on the ECs effects on sperm production, morphology, genome,and motility kinetics. After a brief introduction to reproductive biology, fertility indicators, anddeterminants of fertility in male fishes, wildlife evidences for reproductive disorders were reviewedin fishes from the polluted aquatic environment. The laboratory studies show that ECs detected inaquatic environment are capable of causing fertility threat at environmentally relevant concentrationsassociated with a decrease in fertility determinant(s). This study suggests an urgent need to betterelucidate mechanisms through which ECs affect sperm functions to cause fertility threat.Abstract:Increasing global rates of diminished fertility in males has been suggested to be associatedwith exposure to environmental contaminants (ECs). The aquatic environments are the final reposi-tory of ECs. As the reproductive system is conserved in vertebrates, studies on the effects of ECson fertility endpoints in fishes provide us with valuable information to establish biomarkers in riskassessment of ECs, and to understand the ECs-related fertility threat. The aim of the present reviewwas to evaluate associations between ECs and fertility determinants to better understand ECs-relatedmale fertility threat in male fishes. Wildlife studies show that the reproductive system has beenaffected in fishes sampled from the polluted aquatic environment. The laboratory studies show thepotency of ECs including natural and synthetic hormones, alkylphenols, bisphenols, plasticizers,pesticides, pharmaceutical, alkylating, and organotin agents to affect fertility determinants, resultingin diminished fertility at environmentally relevant concentrations. Both wildlife and laboratorystudies reveal that ECs adverse effects on male fertility are associated with a decrease in spermproduction, damage to sperm morphology, alternations in sperm genome, and decrease in spermmotility kinetics. The efficiency of ECs to affect sperm quality and male fertility highly dependson the concentration of the contaminants and the duration of exposure. Our review highlighs & nbsp;that the number of contaminants examined over fertility tests are much lower than the number ofcontaminants detected in our environment. The ECs effects on fertility are largely unknown whenfishes are exposed to the contaminants at early developmental stages. The review suggests the urgentneed to examine ECs effects on male fertility when a fish is exposed at different developmental stagesin a single or combination protocol. The ECs effects on the sperm genome are largely unknownto understand ECs-related inheritance of reproductive disorders transmitted to the progeny. Toelucidate modes of action of ECs on sperm motility, it is needed to study functional morphology ofthe motility apparatus and to investigate ECs-disrupted motility signaling.