A NEW SHORT-TERM MYSID TOXICITY TEST USING SEXUAL MATURITY AS AN END-POINT

The estuarine mysid, Mysidopsis bahia, is widely used in establishing acute and chronic toxicity of saline aqueous samples. Survival, growth and fecundity are some of the common endpoints analyzed in short-term chronic toxicity tests. The present study proposes use of a new sublethal endpoint, sexual maturity. A mysid is considered to be sexually mature if it shows presence of gonads that can be clearly distinguished as the testis or the brood sac. This endpoint can be measured by a K-factor, defined as the ratio of the total number of mysids achieving sexual maturity to the total number of surviving mysids. Three sets of parallel tests were conducted using cadmium chloride as a toxicant. Both tests in each set were initiated simultaneously using 8-day-old mysids. One of the two tests in each set was terminated after 96 h of exposure with survival, growth and sexual maturity evaluated as endpoints. The second test from each set was conducted over a 7-day period and survival, growth, fecundity and sexual maturity were evaluated as endpoints. Results indicate that sexual maturity is a sensitive endpoint and can be used as an estimator of chronic toxicity.