Zebrafish sperm toxicity tests: An emerging in vitro and in vivo model for male reproductive toxicity

Male reproductive toxicity tests are a standard component of toxicological research, regulatory and safety assessment during drug development and environmental biomonitoring. Zebrafish (Danio rerio) has emerged as a valuable model for studying male reproductive toxicity, particularly through sperm toxicity tests. Thus, this review systematically analyzed the scientific literature concerning the Zebrafish Sperm Toxicity test (ZST), focusing on the effects of environmental chemicals on sperm quality and reproductive health. Results showed that over 80 chemicals have been studied for their adverse effects on zebrafish sperm, including synthetic estrogens, metals, pesticides, and antibiotics. Several endocrine disruptors, such as bisphenol A (BPA) and tributyltin (TBT), impairing sperm count, motility, and morphology by disrupting hormonal regulation and inducing oxidative stress. Methodological approaches were discussed, including sperm collection techniques and storage media, which are critical for experimental reproducibility. Exposure times vary widely, with chronic and long-term exposures being more common in in vivo studies, while in vitro studies typically involve shorter exposure periods. The most frequently adverse effects on zebrafish sperm were reduced sperm count, volume or density, motility, DNA and membrane integrity, and morphological alterations, with endocrine disruption being a primary mechanism of action and toxicity. The review underscores the need for standardized protocols and further research on emerging pollutants, transgenerational effects, and the development of advanced in vitro models to reduce reliance on in vivo experiments. Overall, the zebrafish sperm toxicity test is a suitable tool for assessing the impact of environmental contaminants on reproductive health, helping to protect human and environmental health.