Phycotoxins: Physiology and Production

Introduction Phycotoxins ([phyco = seaweeds and algae] plus toxins) are a diverse group of poisonous substances produced by various aquatic plants in marine and fresh waters throughout the world. Not all aquatic plants produce toxins; and among those that do, not all, even from the same genera and species, produce toxins at all times and under all circumstances. In addition, problems with toxins occurring in shellfish are experienced commonly when no algal blooms have been noted, e.g. much of the chronic Paralytic Shellfish Poisoning in the Bay of Fundy, the recorded instances of Diarrhetic Shellfish Poisoning on the Nova Scotian south shore, and the domoic acid in scallops from Georges Bank in 1995 to name a few. The problems caused by phycotoxins in freshwater are often the result of blooms of cyanobacteria (formerly known as bluegreen algae) which make the waters toxic, resulting in large losses among wildlife and domestic animals. In the marine environment the most newsworthy occurrences have been major intoxications among people who have eaten filter-feeding shellfish (molluscs) which have fed on toxigenic algae, thereby accumulating large amounts of the toxins. Many of these toxic episodes have resulted in fatalities and others in temporary and permanent disabilities. In addition, a number of studies have implicated marine toxins in large fish kills in the wild (adult and larval fish), major kills of marine mammals (whales, porpoises, and seals), as well as threats to cage cultured finfish, e.g. the microcystin-like toxin causing Netpen Liver Disease resulting in serious mortalities among farmed salmon.