Histopathology of Zebrafish (Danio rerio) in Nonclinical Toxicological Studies of New Drugs

Zebrafish ( Danio rerio ) is a small-sized teleost fish natural of tropical regions, with a short life cycle and high homology toward humans. These features make zebrafish an attractive and promising model organism for nonclinical tests due to the ease of handling and cost–benefit compared to other models. The digestive, cardiovascular, urinary, nervous, and reproductive systems of zebrafish display feature similar to those of superior mammals, and due to its susceptible organs, the adult zebrafish has been used to test the toxicity of environmental compounds and potential drug candidates through histopathology analysis complementarily with other parameters. In such cases, the choice of the organ assessed relies on the type of compound tested, administration route, and biological activity. This chapter brings together histopathological nonclinical toxicity studies performed exclusively with zebrafish, highlighting significant histological changes found in its gills, liver, kidneys, and intestine. Based on the information presented here, it is expected that the researcher recognizes differences between healthy and changed tissue, without having to compare its result with other species.