Fish kills induced by phycotoxins.
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文摘
A bloom of 1.3 × 108 cells/litre of the phytoplanktonic organism Heterosigma carterae occurred near the tip of Cap Finisterre, Brittany. It was associated with a mass mortality of salmonids, farmed in cages at Camaret. A large part of them was lost over 2 days in September 1994. All of the Atlantic salmon and some of the salmon trout succumbed. Heterosigma carterae is known to produce a water-soluble ichthyotoxin. At about the same time in Tunisia, north of Sfax in the Gulf of Gabès, a bloom of the alga Gymnodium sp. with up to 60 × 106 cells/litre killed practically all the wild fish. This event occurred over 10 days during October 1994. ThisGymnodium sp. appears close to G. cf nagasakiense, which has well-known ichthyotoxic effects. Its toxin is a glycolipid, of which one of the components is the polyunsaturated fatty acid, C18-5n3, also characteristic of G. cf nagasakiense. In the events both in Brittany and Tunisia, the fish showed signs of respiratory distress, spasms and episodes of excitement with disorientated swimming, then they turned over and died within a half to several hours. In both cases, histological investigation revealed lesions, mostly involving the branchial epithelium. Unlike in previous reports, however, the lesions were of limited extent. In both cases, haemolytic tests were carried out, after filtration, on water taken from the blooms. The results showed only slight activity for the Brittany event, but very marked activity in Tunisia. From literature searches and observations made in Tunisia, fish kills are sometimes accompanied by mortalities of birds that have eaten the fish. However, no allusion appears to have been made to any effects in humans who ate the fish during blooms, in either a healthy or a weakened state. This suggests a similarity between the toxic actions of the two species during blooms, even though the chemical nature of the active molecules appears to be quite different.