or red tide, a phenomenon characterized by a sudden, rapid multiplication
of algal cells caused by environmental factors not yet fully understood.
The phycotoxins are taken up by predators feeding on plankton, either
directly as in the case of bivalve molluscs, or through several trophic
levels as in fi sh. Man then consumes these food items. Marine biotoxins
are responsible for a substantial number of seafood- borne diseases. The
known toxins are shown in Table 4.9.
Table 4.9 Aquatic biotoxins
Where /when produced
in fi sh ante mortem, feed,
pufferfi sh ( Tetraodontidae ) mostly ovaries,
> 400 tropical/subtropical fi sh sp.
shellfi sh poison
fi lter feeding shellfi sh, mostly digestive
glands and gonads
fi lter feeding shellfi sh
” ” ”
” ” ” (blue mussels)
Shellfi sh and crabs edible tissue, viscera
The toxins and the diseases they can provoke have been described and
reviewed by Taylor (1988), Hall (1991), WHO (1984, 1989) and Todd (1993).
Some of the more important aspects are discussed below.
Unlike all other biotoxins algae do not produce tetrodotoxin that accumulate
in live fi sh or shellfi sh. The precise mechanism in production of this very
potent toxin is not clear, but quite commonly occurring symbiont bacteria
are involved (Noguchi et al., 1987; Matsui et al., 1989). Tetrodotoxin is
mainly found in the liver, ovaries and intestines in various species of
puffer fi sh, the most toxic being members of the family Tetraodontidae , but
not all species in this family contain the toxin. The muscle tissue of the
toxic fi sh is normally free of toxin, but there are exceptions. Puffer fi sh
poisoning causes neurological symptoms within 10-45 min after ingestion.
Symptoms are tingling sensation in face and extremities, paralysis,
respiratory symptoms and cardiovascular collapse. In fatal cases death
takes place within 6 h.
Ciguatera poisoning results from the ingestion of fi sh that have become
toxic by feeding on toxic dinofl agellates, which are microscopic marine
planktonic algae. The principal source is the benthic dinofl agellate
Gambierdiscus toxicus , which is living around coral reefs closely attached