Effects of ethyl carbamate (urethan) on the early development of the teleost Brachydanio rerio.

Abstract

1. Six typical developmental stages of the teleost, Brachydanio rerio , namely: early cleavage, blastulation, early to mid-gastrulation, late gastrulation (closure of the blastopore), optic vesicle, and optic cup were subjected to concentrations of 0.05–1.25 per cent urethan (ethyl carbamate) for periods varying from 4 to 32 hours and continuously. 2. The chorion is freely permeable to urethan, as evidenced by the fact that no significant differences in susceptibility occur when it is pricked. 3. Retardation of both growth and differentiation of embryonic structures occurs in concentrations of 0.25 to 1.25 per cent and results in the production of anomalies. 4. The effects are cumulative and proportional to the concentration, the duration of exposure, and to some extent the initial stage of development on subjection. The sensitivity, in general, decreases with age and differentiation. 5. No special type of teratological embryo is exhibited, but the results are consistent and reproducible. Developmental abnormalities include: edema of the coelomic cavities and hydropic degeneration of various body tissues, cardiac and systemic circulatory irregularities, disorganization and lack of differentiation of the central nervous system and the eye, malformation of the notochord and musculature, atypical pigmentation, and epithelial hyperplasia. 6. Vascular stasis in the extra-embryonic area and, more especially, the occurrence of extensive epithelial hyperplasia of the epidermis may be indicative of specific effects of the urethan, while the other anomalies resemble types resultant upon the application of a variety of physical and chemical agents to the developing embryo.