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Seal Worms in Fish

Small round worms, varying in color from creamy white to dark brown, are occasionally found in the flesh of fish, particularly cod. These seal worms, or nematodes as they are called by scientists, also known as Terranova decipiens or Porrocaecum decipiens, spend part of their life cycle in seals. Eggs passed into the water by seals hatch, are eaten by small fish and shrimp-like animals which are in turn eaten by larger fish such as cod. Only fish caught in areas frequented by seals are affected in this way and only a small portion of the total catch is taken from such areas.

The occurrence of nematodes in fish is a natural phenomenon which cannot be prevented and is not indicative of mishandling or spoilage. Fillets from fish taken from areas where seals abound are carefully examined by passing them over an illuminated glass top table. The light shining through the fillets aids in the detection and reduces the chances of fillets containing seal worms reaching the consumer. While the operation is routinely checked by federal government inspectors, it is not 100% effective and in spite of taking every reasonable precaution, fillets containing the worms do reach the market.

The seal worm is destroyed by commercial freezing and storage as well as by normal cooking temperatures. Fish is fully cooked when the colour of the flesh becomes opaque and flakes easily when tested with a fork.