Infection levels of two ascaridoid nematodes (Anisakis simplex and Pseudoterranova decipiens) in Atlantic cod (Gadus morhua) off Newfoundland and Labrador, and on the Flemish Cap.

Parasitic nematodes infecting the flesh of commercially important fish species pose an aesthetic and economic problem for the fishing industry. They also have potential health implications as they may cause disease in humans. The musculature of 811 Atlantic cod (Gadus morhua) from five cod stocks in the Northwest Atlantic off Newfoundland and Labrador, and on the Flemish Cap, were examined for two ascaridoid nematodes, Anisakis simplex sensu lato and Pseudoterranova decipiens sensu lato. I evaluated the distribution of these nematodes within the musculature of Atlantic cod, and investigated whether prevalence, abundance, or density varied among cod stocks or in relation to fish length. I used similar examination techniques to previous studies conducted during the 1940-50s and the 1980s, and compared infection levels to these studies. In all areas, prevalence and abundance of A. simplex s.l. increased substantially relative to historical studies. The highest infection levels of A. simplex s.l. were observed in fish from Northwest Atlantic Fisheries Organization (NAFO) Division 3M. The results are consistent with a possible increase in abundance of some cetaceans, the definitive hosts of A. simplex s.l.; although population trends of most cetaceans are not well known. In most areas, infection levels of P. decipiens s.l. also increased since the 1980s. The area with the highest abundance of P. decipiens s.l. was the west coast of Newfoundland (Divisions 3Pn4R). Greater abundances could be related to an increase in abundance of grey seals (Halichoerus grypus) that serve as definitive hosts. Major changes in marine food webs following the collapse of groundfish stocks in the late 1980s and early 1990s, as well a