HEAVY METAL. CONCENTRATIONS IN SEA WATER FROM GRASS PRAWN HATCHERIES AND THE COAST OF TAIWAN

Abstract

Of the 1500 million postlarvae produced last year, the average survival rate was estimated at lower than 20%. The intent of this study was to examine heavy metal as a potential contributory factor to their mortality. Although the concentrations of heavy metals in most areas were lower than the maximum permissible levels recommended by Japanese Fishery Agency and U.S. Coastal Sea Water Quality Criteria. Those hatheries with the lowest survival rates, however, were at Chyijin peninsula of Kaohsiung where the waters contained significantly high concentrations of iron and heavy metals.

Since most of the prawn hatchery farmers buried the inlet pipe under the sand beach and pumped the sea water from beneath the ground in the tidal zone instead of using coastal sea water directly, both waters were analyzed. The results indicated that except for manganese, the heavy metals in the coastal sea water were in higher concentrations than those in underground sea water. The higher manganese concentration found in the underground sea water was probably caused by dissolution from the manganese-containing sediments. Pretreatment of sea water before use was recommended.