Seafood Safety

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The conditions best suited for toxic dinoflagellate growth are not well understood. There have been a number of conflicting observations concerning optimal growth conditions, some of which are as follows:

  1. G. toxicus is negatively influenced by land runoff and high light intensity (Yasumoto et al., 1980 as cited in Carlson and Tindall, 1985).
  2. Dinoflagellates replicate rapidly when disturbed, such as, after major storms, and areas of construction or dredging (Craig, 1980).
  3. Highly toxic sites seem to be toward the leeward side of islands.
  4. Populations of dinoflagellates are affected by rainfall in varying degrees. Moderate rainfall may promote dinoflagellate growth by increasing dissolved nutrients in the water, through increased terrestrial runoff. However, heavy rainfall may inhibit growth by increasing dilution and/or turbidity (Carlson and Tindall, 1985).
  5. G. toxicus may specifically associate with macroalgae where high concentrations of nutrients are available for growth (Carlson and Tindall, 1985).
There are at least four known toxins which appear to be concentrated in the viscera, head or central nervous system of affected fish (Tosteson et al., 1988): ciguatoxin, scaritoxin, maitotoxin and ciguaterin. Ciguatoxin, the principal toxin, is lipid soluble (Kantha, 1987). Studies indicate that oral intake of as little as 0.1ug (11MU) of ciguatoxin could cause illness in an adult human (Yasumoto, 1985). Maitotoxin is water soluble and approximately three times more toxic than ciguatoxin (Yasumoto, 1985).

Contaminated Species

Tropical and subtropical coral reef fish can become ciguatoxic. The incidence of poisonous fish, however, is sporadic. All fish of the same variety and caught in the same area may not necessarily be toxic (Hokama et al., 1983). A study done in Hawaii indicated that if fish in one location are toxic, other fish in the vicinity are approximately 60% likely to be toxic. Both herbivorous and carnivorous fish can become toxic. Herbivorous fish become toxic by eating the toxic algae itself. Carnivorous fish become toxic by consuming toxic herbivorous fish. Generally, large fish are more poisonous than small fish because they consume greater amounts of the toxins (Craig, 1980). The fish most often implicated in cases of ciguatera include: barracuda (Olson et al., 1984 as cited in Tosteson et al., 1988); grouper (Craig, 1980; Lawrence et al., 1980); snapper (Craig, 1980; Lawrence et al., 1980); surgeon fish (Miyahara et al., 1987); jack (Craig, 1980; Hokama et al., 1983; Miyahara et al., 1987); and parrot fish (Bryan, 1986; Bryan, 1988).

Geographic Area

Ciguatera is found world-wide in fish between 35N and 34S latitude (Craig, 1980). It is a problem in the South Pacific, Japan Islands, U.S. and Bahamas. The only areas of the U.S. affected by ciguatera are: Florida, Hawaii, Puerto Rico and the U.S. Virgin Islands. There is evidence that ciguatoxic dinoflagellate populations experience seasonal fluctuations. In Hawaii ( ) and the Virgin Islands (Carlson and Tindall, 1985), the algae exhibits a bimodal pattern of abundance with population maxima occurring in conjunction with the peak periods of rainfall; April to May, and August to October. Studies in Puerto Rico indicate that populations of Ostreopsis lenticularis and Gambierdiscus toxicus experience a seasonal trend, although densities are highly variable (Ballantine et al., 1988). Peak populations tend to occur during the late summer and fall, and do not appear to be correlated to rainfall. Although additional data are needed, there appears to be a seasonal fluctuation in the toxicity of Ostreopsis as well. In a three year period in Puerto Rico, toxicity of Ostreopsis ranged from nontoxic to 182 MU/1,000,000 cells. In two of the three years, peak toxicities occurred in October.

Symptoms & Treatment

Ciguatera exhibits both gastrointestinal and neurological symptoms (Lawrence et al., 1980). The time of onset is usually less than 24 hours. Gastrointestinal symptoms, which usually persist for 12 hours (range < 1 hour - 7 days), include: diarrhea, abdominal pain, nausea and vomiting. The most common neurological symptoms include: paresthesia (abnormal or impaired skin sensations), vertigo, ataxia (lack of muscle coordination), cold-to-hot sensory reversal, myalgia (muscular pain), itching (especially during any activity that increases skin temperature and blood flow). Neurological symptoms may recur intermittently with gradually diminishing severity for a long as six months. No deaths have been reported from ciguatera in the U.S. (Morris, 1980), although world-wide the mortality rate of ciguatera is 7-20% (Craig, 1980).

Ciguatera from consumption of herbivorous fish has reportedly been associated with more severe gastrointestinal complaints, whereas neurological and cardiovascular effects often predominate in poisoning by carnivores (Bagnis, 1968 as cited in Miyahara et al., 1987). This observation was supported in a study which demonstrated that different species of ciguatoxic fish accumulate different toxins (Miyahara et al., 1987).


World-wide, there may be as many as 50,000 cases of ciguatera per year (Ragelis, 1984). In the U.S., between 1970 and 1980, 94 outbreaks (418 cases) of ciguatera were reported to the CDC, making it the most frequently reported food-borne illness associated with consumption of seafood (Morris, 1980).

Detection & Prevention

MOUSE BIOASSAY (Kimura et al., 1982) - For lack of a better technique, the mouse bioassay is currently the laboratory method used to detect ciguatera. Concentrated lipid extracts of fish tissue are injected intraperitoneally into a 20 g mouse and the mouse is observed for toxic symptoms for 24 - 48 hours. Listed below are a number of general disadvantages of the mouse bioassay to detect marine toxins:

A number of other laboratory methods have been suggested as a replacement for the mouse bioassay and are described below:
MOSQUITO BIOASSAY (Chungue et al., 1984) - Toxins are extracted from fish and injected intrathoracically into mosquitoes. The mosquitoes are observed for one hour for signs of death. This technique requires only a small amount of fish tissue and results can be obtained within 2 hours.
IN VITRO GUINEA PIG ATRIUM ASSAY (Miyahara et al., 1979 as cited in Kimura et al., 1982) - Crude lipid extracts of fish are added to an isolated guinea pig atrium. The effects are expressed as the ratio of the amplitude of contraction occurring after the addition of extract as compared to the initial amplitude of untreated atrium.
"STICK" TEST (Hokoma et al., 1985; Hokoma et al., 1987a; Hokoma et al., 1987b; Hokoma et al., 1989) - Bamboo sticks, pretreated to help adsorb the toxin, are stuck into the fish flesh for 1 second. The sticks are then fixed with methyl alcohol and immersed in a solution of blue latex beads and ciguatoxin antibody. A positive result will change the bamboo stick to a dark-blue or purple color within 10 minutes. This procedure does not require extraction of tissue (although it is capable of testing extracted tissue), gives rapid results, and is inexpensive.
RADIOIMMUNOASSAY (Hokama et al., 1977; Kimura et al., 1982) - Sheep anti-ciguatoxin serum coupled with iodine-125 is added to a sample of fish tissue extract. Excess antibody is removed and the samples are analyzed with a scintillation counter. If ciguatoxin is present in the fish flesh, the DPM will be high. If the fish is free of toxin the DPM will be low. This procedure is sensitive and relatively specific, however, it is economically unfeasible for testing fish weighing <9 kg (Hokama et al., 1983).
ENZYME-IMMUNOASSAY (Hokama et al., 1983) - Sheep anti-ciguatoxin serum coupled to horseradish peroxidase is added to a sample of fish tissue extract and incubated at room temperature for 1 hour. The amount of toxin in the tissue is determined by measuring the absorbance at 405 nm.
Ciguatera toxins impart no unusual tastes, odor or color to the fish (Craig, 1980) and ciguateric fish cannot be made safe to eat by cooking, freezing, drying or smoking (Tosteson et al., 1988). Listed below are methods which have been suggested to avoid ciguatera:

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