The 'herring worm' is often found in herring, mackerel, whiting and blue whiting, but it also occurs in many other species. Its scientific name is Anisakis simplex. It grows up to 2 cm long in fish, is almost colourless, and is found tightly coiled and encased in the guts and flesh, sometimes in considerable numbers, particularly in the belly flaps. Anisakis can migrate from guts to flesh in fish left ungutted after capture, notably in herring, mackerel and blue whiting.
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