Safety Hazards- Seafood

Seafood is subject to a wide range of safety hazards, some of which are unique to seafood. Fortunately, most are controllable and occur infrequently, although in some cases the controls are not easy and better ones are needed.

Bacteria
Other than raw molluscan shellfish, seafood is only rarely a source of illness caused by bacteria from the environment. Most pathogens are introduced in the processing environment. As aquaculture becomes a more important source of food, however, care must be taken that bacteria are not carried from contaminated ponds to workers and consumers.

Viruses
Several viruses infectious to humans enter aquatic habitats through sewage. Most concentrate in shellfish and can be present and infective even when bacterial indicators of fecal pollution are absent. Viruses probably cause the bulk of seafood-associated disease, particularly the Norwalk agent, which is linked to the consumption of raw or undercooked molluscan shellfish. Viruses can also be introduced during handling by food plant workers.

Toxins
After Norwalk virus, the two most frequently reported illnesses from seafood are from toxins. The first is scombroid poisoning, which occurs as a result of decomposition in certain species of finfish, primarily tuna, mahi-mahi and bluefish. It is completely preventable through good handling practices. The second is ciguatera poisoning from consuming predatory, tropical and subtropical-fish such as grouper, snapper, barracuda, and Spanish mackerel. These toxins originate in marine algae and can be concentrated by passage along the food chain. Ciguatoxic fish are generally confined to very localized geographic areas where blooms of the algae occur.

Parasites
Parasites such as the anasakine nematode (round worm) naturally infect many fish and ocean mammals. When human infections from marine parasites occur it is almost always from the consumption of raw fish (sushi, sashimi) or undercooked fish. These infections could be completely avoided by adequate cooking or by commercial freezing if the fish is to be consumed raw.

Chemical Contaminants
The presence of toxic chemicals in the aquatic environment leads to the potential for contamination of fish and shellfish. These chemicals include pesticides, other industrial chemicals such as polychlorinated biphenyls (PCB's) , heavy metals (such as lead, cadmium, and mercury), and petroleum hydrocarbons. Marine species, especially deep sea varieties, comprise the majority of commercial fish consumed in this country. Generally speaking, these fish have little potential to contain chemical contaminants at levels of toxicologic concern. Fresh water and estuarine species, especially non-migratory bottom feeders, are generally the most exposed to a variety of chemical contaminants.

References: http://www.hhs.gov/asl/testify/t960522b.html