**1. Introduction**

Toxicology is the science of researching on the negative effects that chemical or physical agents may exert on living organisms under particular exposure conditions. It is a science that attempts to evaluate all the hazards, such as molecular toxicity, cytotoxicity, organ toxicity, etc., that are associated with a substance, as well as to quantitatively determine the exposure conditions under which these hazards or toxicities are induced [1, 2]. Additionally, toxicology is the science that studies the occurrence, character, frequency, mechanism, and risk elements associated with the adverse effects of toxic substances [2].

Many biological models can be applied for toxicity evaluation. Cell culture system is often used in vitro because it is economical and time-saving. But it is very difficult to infer the health of the whole organism, including humans, only from the results of in vitro cell tests. On the contrary, in vivo studies may provide improved prediction of biological reactions in intact systems (whole animal) but are generally expensive, time-consuming, and often elaborate, requiring extensive facilities and infrastructure [3]. Zebrafish (*Danio rerio*), as a classical model vertebrate organism, offers many practical advantages that can overcome these limitations to be highly suitable for application in toxicologically relevant research. Zebrafish can be employed as an outstanding in vivo model system to evaluate biological reactions and is a powerful platform to analyze in detail the mechanisms by which substances induce specific biological responses. Further, conditions in high-order vertebrates can be inferred from the results obtained using zebrafish because there

is a remarkable similarity in cellular structure, signaling processes, anatomy, and physiology, particularly in the early stages of development [4–8]. Current estimates show that more than 90% of the human open reading frames are homologous to those in the genes of this fish [9]. Thus, investigations using this model system can reveal subtle interactions that are likely to be conserved across species.
