What is one of the main limitations of Danio rerio, the zebrafish in toxicity studies? Embryos are transparent Only 82% of its genes are related to human diseases It requires an aqueous environment The shell of the egg is impermeable to toxins

The main limitation of zebrafish in toxicity studies out of the options provided is that **Only $82\%$ of its genes are related to human diseases.**<br /><br />While zebrafish are a popular model organism due to their transparent embryos, quick development, and ease of genetic manipulation, the fact that not all their genes have human homologs means that they may not always accurately reflect human responses to toxins. A toxic effect observed in zebrafish might not occur in humans, or vice versa, due to these genetic differences. The other options are not limitations: transparent embryos are an advantage, the aqueous environment is their natural habitat, and the chorion (shell) is permeable to many toxins, making them useful for study.<br />