Ichthyotoxicity studies of milkfish Chanos chanos fingerlings exposed to aharmful dinoflagellate Alexandrium minutum

Milkfish (Chanos chanos Forsskal) fingerlings were treated with toxic, nont oxic dinoflagellate Alexandrium minutum cells or toxic algal extract in the water medium without any aeration, Mortality of fish increased with increa sing concentrations of toxic, nontoxic algal cells and water-soluble toxic algae extract, Milkfish fingerlings, which were exposed to toxic algae (1.5 X 10(4)-3.0 X 10(4) cells/ml) or algal extract [5.13 X 10(3)-2.05 X 10(4) cells/ml, 0.195 MU/10(4) cells (toxin concentration)] for 24 h, revealed by light microscopic observations a noticeable edema, hyperplasia and necrosi s of secondary gill lamellae. The same toxicological symptom was observed i n fish exposed to pure saxitoxin (STX) (6.475 X 10(-2) mug/ml) in the water medium. A higher critical oxygen pressure and oxygen consumption rate were also found in the milkfish fingerlings exposed to toxic algae extract (5.1 3 X 10(3)-2.05 X 10(4) cells/ml:) and STX (6.475 X 10(-2) mug/ml). The cell s of nontoxic A. minutum did not cause the gill damage to milkfish, and the extract of nontoxic algae did not cause an increase in oxygen consumption rate or critical oxygen demand of milkfish, From these results, we infer th at toxic cells and its: extract cause nonspecific response in gill tissues of milkfish. An instant increase in oxygen consumption rate and oxygen dema nd may be one of the major causes of fish death. (C) 2001 Elsevier Science B.V. All rights reserved.