Variation and classification of chemically-induced zebrafish malformations for the ICH S5 (R3) guideline: an atlas for zebrafish teratogenesis.

Exposure of embryos or fetuses to harmful substances, such as teratogens, can result in embryonic or fetal death and a wide range of malformations. Zebrafish models have emerged as a valuable tool for assessing developmental toxicity and safety profiles of chemical compounds. Our previous research demonstrated that zebrafish larvae exhibit developmental abnormalities that mirror those observed in mammalian studies for more than 80% of the known Reference Compounds listed in the ICH S5 (R3) guideline. In this study, we presented high-resolution images depicting pharmaceutical-induced malformations across multiple anatomical regions, including the body axis, somites, notochord, fins, head, eyes, otoliths, jaw, heart, abdomen, and whole body. Frequent co-occurrence of specific defects, such as body axis and notochord malformations, was observed as described previously. Some physiological and morphological features, including heartbeat rate alterations and swim bladder inflation, were deemed dispensable for MEFL testing in zebrafish. Reproducibility was confirmed through inter-laboratory testing conducted both within our group and by other groups, supporting the reliability of zebrafish MEFL testing as an alternative approach in line with ICH S5 (R3).