Seafood Safety

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Detection & Prevention

Toxins in shellfish cannot be destroyed by normal cooking, freezing or smoking. The best prevention of DSP is by detecting the toxins in shellfish before they reach the market. The following are methods which are currently used, or are being developed, for the detection of DSP:
RAT BIOASSAY (Hagel, 1990) - This technique is currently used in the Netherlands to monitor DSP. White rats are fed the hepatopancrease of suspect shellfish and observed. Consistency of the feces and refusal to consume the shellfish are used to test for the presence of DSP toxins.
SUCKLING MOUSE ASSAY (Humano et al., 1985) - The suckling mouse assay is based on the fluid accumulation in the mouse intestine as a reaction to the acidic toxins (okadaic acid and dinophysistoxin -1 and -3). Shellfish extract is intragastrically administered to 4 - 5 day old mice. After 4 hours the mice are sacrificed, the intestine removed and the fluid accumulation ratio (expressed as the ratio of intestinal weight to remaining body weight) is determined. This method is more sensitive to DSP toxins and less influenced by free fatty acids and other contaminants than the mouse bioassay. However, it requires maintaining a mouse colony and it is difficult to obtain a quantitative estimate of the amount of DSP toxin present (Sullivan, 1988).
CYTOTOXICITY ASSAY (Underal et al., 1985, as cited in Sullivan, 1988) - This procedure is based on measuring the leakage of lactate dehydrogenase from rat hepatocytes following treatment with an extract of shellfish tissue.
HPLC (Lee et al., 1987) - Shellfish extracts are esterified with 9-anthryldiazomethane (ADAM) and analyzed with an HPLC. This method is most effective when okadaic acid and Dinophysistoxin -1 are the principal toxins, and is limited in its ability to detect the other toxins.
STICK TEST - The stick test used to detect DSP is based on an enzyme immunoassay procedure and can detect nanogram levels of okadaic acid.

Puffer Fish Toxicity


Puffer fish, also called fugu or blowfish, contain the potent toxin, tetrodotoxin. It is unclear whether the fish itself produces the toxin, or like ciguatera, it is introduced to the fish by ingestion of toxic algae. Tetrodotoxin acts on both the central and peripheral nervous systems (Kantha, 1987).

Contaminated Species

There are approximately 80 species of puffer fish which are known to contain tetrodotoxin (Kantha, 1987). The domestic species of puffer, sometimes called sea squab, is much less poisonous than the Japanese species, but should be handled by experienced chiefs only.

Geographic Area

Puffer fish are found in the Pacific, Atlantic and Indian Oceans. Cases of puffer fish poisoning occur most commonly in Japan where fugu is considered a delicacy.

Symptoms & Treatment

Symptoms of poisoning usually begin within 10 minutes of consuming puffer fish. The victim first experiences numbness and tingling of lips, tongue and inner surfaces of the mouth. This is followed by weakness, paralysis of limb and chest muscles, decreased blood pressure, and quickened and weakened pulse. Death can occur within 30 minutes (Horwitz, 1977; Kantha, 1987).

Cases of puffer fish poisoning should be treated by maintaining adequate respiration, circulation and renal functions. There is some evidence that recovery of muscle power is accelerated by administration of an anticholinesterase (Torda et al., 1973 as cited in Kantha, 1987).


From 1972 to 1974, there was one outbreak, involving two cases, of puffer fish poisoning reported to the CDC (Horwitz, 1977). According to USFDA reports there are an average of 19 fatalities from puffer fish poisoning in Japan each year (Anonymous, 1989). Other sources report that puffer fish toxicity is the number 1 cause of fatal food poisoning in Japan and is responsible for approximately 100 fatalities/year (Anonymous, 1989).

Detection & Prevention

In Japan, chefs are required to have at least three years experience before they are allowed to handle fugu. According to Japanese reports, no cases of poisoning have been attributed to puffers prepared by certified chefs. Problems only occur when inexperienced individuals try to prepare fugu (Anonymous, 1989).

The USFDA has recently lifted an import ban on one type of puffer fish, the tiger fish. Unlike some species of puffer, which may have toxins in the entrails, liver, ovaries, skin and muscle; tetrodotoxin is only found in the liver of the tiger fish (Anonymous, 1989). Before importation to the U.S., the FDA requires that all tiger fish are cleaned, toxic tissues are removed and fish are laboratory certified to be tetrodotoxin-free. Japanese chefs preparing the fish for export to the U.S. are required to have at least 13 years of experience in handling fugu.


Anisakis Simplex or Herring Worm


Anisakis simplex, commonly called herring worm, is a parasitic nematode whose final hosts are dolphins, porpoises and sperm whales (Oshima, 1972, as cited in Pinkus et al., 1975). In the larval stage, the stage which infects fish, the parasite is usually 18-36 mm in length, 0.24-0.69 mm in width and whitish in color (Pinkus et al., 1975). Anisakis larvae are more prevalent in the Pacific than the Atlantic since the Pacific has a large population of whales, one of the final hosts of Anisakis (Myers, 1979; Schantz, 1989).
Humans are accidental hosts of Anisakis larvae. Anisakiasis, the illness caused by Anisakis simplex, is associated with the presence of a marine mammal population and eating raw or undercooked fish (sushi, sashimi, lomi lomi, ceviche, sunomono, Dutch green herring, marinated and cold smoked fish).

Contaminated Species

Generally, both prevalence and intensity of Anisakis infection increase with size and age of fish (Smith and Wootten, 1978; McGladdery and Burt, 1985 as cited in McGladdery, 1986). Those species which feed primarily on benthic organisms have a lower incidence of Anisakis contamination, while fish that predominantly feed on other fish generally have a high incidence of contamination (Myers, 1979). The types of fish commonly infected with Anisakis larvae include: herring (Hauck, 1977; Smith, 1984; Schantz, 1989); Atlantic and Pacific cod, (Myers, 1979; Rodrick and Cheng, 1989; Schantz, 1989); Pacific salmon (Deardorff et al., 1986; McKerrow et al., 1988); sole (Myers, 1979; and Cheng, 1976 as cited in Roderick and Cheng, 1989); mackerel (Schantz, 1989; Smith, 1984); pollock (Smith, 1984); whiting (Smith, 1984); bonito (Pinkus et al., 1975); squid (Pinkus et al., 1975; Olson, 1986; Oshima, 1987); and Pacific rockfish (Schantz, 1989; McKerrow et al., 1988).

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