DECREASED TOXICITY OF COPPER AND MANGANESE IONS TO SHRIMP NAUPLII (Penaeus stylirostris STIMPSON) IN THE PRESENCE OF EDTA

Abstract

AbstractAlthough ethylenediaminetetraacetic acid (EDTA) is used routinely in the intensive culture of penaeid shrimp larvae to increase both the percentage of eggs that hatch and the survival of larvae, the mode of action is not known. To explain EDTA's beneficial effect this study compares the toxicities of copper and manganese divalent ions in the presence and absence of 10 mg EDTA/liter seawater. Toxicity was evaluated in terms of the percentage of Penaeus stylirostris nauplii surviving after 12 and 24 hours of exposure to either copper or manganese and in terms of the percentage of nauplii that metamorphose to the protozoeal stage.In the absence of EDTA, copper and manganese ions were toxic to nauplii with copper causing 100% mortality at a much lower concentration (20 μM) than manganese (20,000 μM). In the presence of EDTA, survival of nauplii exposed to copper was increased but survival of nauplii exposed to manganese was not affected.At concentrations lower than the levels that reduce survival, copper ions (0.2 μM) and manganese ions (2 μM) reduce the percentage of nauplii that metamorphose to protozoea. In the presence of EDTA, the percentage of nauplii that metamorphose to protozoea is increased with both nauplii exposed to copper ions and nauplii exposed to manganese ions.The beneficial effects of EDTA are probably due to the chelation of copper and manganese ions by EDTA. Chelation lowers the free concentration of these ions and thus reduces their toxicities.