ASSESSMENT OF THE ESTUARINE HERMAPHRODITIC FISH RIVULUS-MARMORATUS ASA USEFUL EURYHALINE SPECIES FOR ACUTE TOXICITY TESTS AS SHOWN USING CADMIUM

The estuarine hermaphroditic teleost Rivulus marmoratus was sensitive to toxic effects of cadmium showing low 96-h LC50 values of 0.8-32.8 m g Cd/L for different life stages at 10 parts per thousand salinity, 25 -degrees-C, and pH 7.0. Toxicity was greater at higher temperatures, a t higher pH, and at lower salinity. Tolerance to cadmium increased aft er pretreatment with a low dose of cadmium, but the effect decreased w hen intervals between pretreatment and challenge treatment were longer than 4 d. The gill lamellae and kidney tubules were the primary targe t organs for acute toxic effects of cadmium in adult fish. These resul ts suggest that R. marmoratus, which is small, physiologically toleran t, hardy, and easy to breed, may prove to be a useful euryhaline model for estuarine metal toxicity studies.