Utility of Toxicity Tests with Embryos and Fry of Fish in Evaluating Hazards Associated with the Chronic Toxicity of Chemicals to Fishes

The hypothesis that concentrations of toxicants safe to fish over their entire life cycle can be estimated from the results of continuous exposure of embryos and newly hatched fry has been examined critically in the light of recent data.  The assumptions underlying the proposed hypothesis appear to be: (a) the chemical does not exhibit significant cumulative toxicity; (b) there is a single mode of action through which the effect of the chemical is manifested in a relatively short time frame; and (c) the effect is most severe on the critical life stages (that is, embryos and newly hatched fry), where parameters such as hatchability, survival, and growth can be measured readily. 

The majority of available data indicate that the hypothesis is valid.  In most cases, estimates of specific application factors derived from exposure of critical life stages reasonably approximate specific application factors empirically derived from chronic toxicity studies with much less cost, effort, and time required.  Other data suggest that exposure of critical life stages of fish can indicate to the researcher certain of those chemicals for which the underlying assumptions are not valid and for which the hypothesis is not applicable.  In all cases, estimates of specific application factors derived from critical life stage studies provide information equal or greater in predictive value than information derived from the use of an arbitrary general application factor.