Studies on the biology of larval nematodes from the musculature of cod and whiting in Scottish waters

Abstract

A total of 1841 cod and 2543 whiting from Scottish waters were examined for the presence of larval nematodes within the musculature. Larval Phocanema were common in the musculature of cod from the west coast of Scotland but rare in fish from the central northern North Sea. Larval Anisakis were most abundant in the musculature of cod and whiting from offshore northern North Sea areas but were much less common in other areas. Phocanema occurred only very occasionally in whiting. Anisakis and Phocanema rarely occurred together in the musculature of individual cod. Observed variations in infections of fish are possibly due to differences in the geographical distribution of the invertebrate and vertebrate hosts of the parasites. There has apparently been a large increase in the infection of cod and whiting with larval nematodes within the last twenty years probably due mainly to a greater abundance of Anisakis.

Infection with larval nematodes increased with age and length of the fish. Most Anisakis from the musculature were found in the hypaxial muscles whereas a much larger proportion of Phocanema occurred in the epaxials. In whiting over half the total burden ofAnisakis were found in the musculature rather than the viscera but in cod most larvae occurred in the latter site. There was a significant positive correlation between numbers of Anisakis in the viscera and musculature of whiting but not of cod. Phocanema was found in a number of fish species which may act as a source of infection for cod.