Hong-Nong Chou1*, and Chih-Yu Chen2, 1Institute of Fisheries Science, and 2Department of Zoology, National Taiwan University, Taipei, Taiwan 10617, Chinese Taipei
Abstract
It was reported frequently that abrupt deaths occurred to the cultured shrimp and fish when Alexandrium minutum bloomed in the ponds. It was also found that fish mortality increased with the increasing of concentrations of algal cell or algal extract when milkfish (Chanos chanos Forsskal) fingerlings were treated with toxic A. minutum or its cell extract without appling any aeration during experiment. Milkfish fingerlings, which were exposed to toxic algae (1.5 x 104 cells/ml~3.0 x 104 cells/ml) or toxic algal extracts (5.13 x 103 cells/ml~2.05 x 104 cells/ml) for one day, revealed a noticeable edema, hyperplasia and necrosis of secondary lamellae in gill by light microscopic observations. Similar toxicological symptoms were also observed in fish treated with pure saxitoxin (6.475 x 10-2mg/ml). At the same treatment it was found the fingerlings showed a higher oxygen consumption rate and a higher demand of critical oxygen pressure. However treating the milkfish finglings with the cells of nontoxic A. minutum or the algal cell extract did not give any damage effect to the gill, nor raise the oxygen consumption rate or critical oxygen demand of the fish. However, finglings died from suffocation in a cell concentration (2.10 x 104 cells/ml) of nontoxic A. minutum without aeration support in 24 hrs. Paralytic shellfish poisoning toxins showed similar stress effects and toxicological damages as heavy metals.
Keywords: Alexandrium minutum, gonyautoxins, paralytic shellfish poisoning toxins, Chanos chanos, ichthyotoxicity