Biology Reference
In-Depth Information
to macroalgae. Increased production of toxic dinofl agellates are seen
when reefs are disturbed (hurricanes, blasting of reefs etc.). More than 400
species of fi sh, all found in tropical or warm waters, have been reported to
cause ciguatera (Halstead, 1978). The toxin accumulates in fi sh that feed
on the toxic algae or larger carnivores that prey on these herbivores. Toxin
can be detected in the gut, liver and muscle tissue by means of mouse-
assay and chromatography. Some fi sh may be able to clear the toxin from
their systems (Taylor, 1988).
Although the reported incidence of ciguatera poisoning is low (Taylor,
1988), it has been estimated that the worldwide incidence may be in the
order of 50,000 cases yearly (Ragelis, 1984). The clinical picture varies
but onset time is a few hours after ingestion of the toxin. Gastrointestinal
and neurological systems are affected (vomiting, diarrhea, tingling
sensation, ataxia, weakness). Duration of illness may be 2-3 d but some
may also persist for weeks or even years in severe cases. Death results
from circulatory collapse and 12% of fatal cases have been reported
(Halstead, 1978).
Paralytical Shellfi sh Poisoning (PSP)
Intoxication after consumption of shellfi sh is a syndrome that has been
known for centuries, the most common being paralytic shellfi sh poisoning
(PSP). PSP is caused by a group of toxins (saxitoxins and derivatives)
produced by dinofl agellates of the genera Alexandrium, Gymnodinium and
Pyrodinium . Historically, PSP has been associated with the blooming of
dinofl agellates (> 10 6 cells/liter), which may cause reddish or a yellowish
discoloration of the water. However, water discoloration may be caused
by proliferation of many types of planktonic species, which are not always
toxic, and not all toxic algae blooms are colored. The dinofl agellates bloom
as a function of water temperature, light, salinity, presence of nutrients and
other environmental conditions. However, the precise nature of factors
eliciting a toxic clone is unknown. Water temperature must be > 5-8°C for
blooms to occur. If temperatures decrease to below 4°C, the dinofl agellates
will survive as cysts buried in the upper layers of the sediments.
Mussels, clams, cockles and scallops that have fed on toxic dinofl agellates
retain the toxin for varying periods of time depending on the shellfi sh. Some
clear the toxin very quickly and are only toxic during the actual bloom,
others retain the toxin for a long time, even years (Schantz, 1984). PSP is
a neurological disorder, and the symptoms, include tingling, burning and
numbness of lips and fi ngertips, ataxia, drowsiness, incoherent speech. In
severe cases death occurs due to respiratory paralysis. Symptoms develop
within 0.5-2 h of a meal and victims who survive more than 12 h generally
recover.
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