Comparison of metazoan parasites of Atlantic cod, Gadus morhua, from three geographical areas of coastal Newfoundland

This study compared metazoan parasites in the digestive tract of Atlantic cod, Gadus morhua , captured from 3 geographical areas off the northeastern (NE), southeastern (SE), and southwestern (SW) coasts of Newfoundland. Samples were obtained by line trawl and frozen after capture, and the digestive tract was subsequently examined for metazoan parasites following conventional parasitological methods. Mean abundance of nematodes, but not the trematodes, and an acanthocephalan was significantly greater in cod taken from the NE than from the SE or SW areas, which were generally similar. Four species of trematodes, 3 nematodes, and an acanthocephalan, Echinorhynchus gadi , were the dominant parasites observed. Differences in mean abundance among samples from different areas might be related to the types of prey consumed rather than to environmental factors. The dominant parasites were probably acquired by cod on the NE coast after feeding on capelin, Mallotus villosus , which serve as paratenic hosts for several helminth species. Previous studies on tagging, feeding, and prevalence of 3 parasites have revealed differences in the populations of cod from the NE than from the SW or SE areas. Results from the present study, indicating geographical differences in parasite mean abundance and prevalence from the digestive tract of Atlantic cod between SW and NE areas, support the view of distinct coastal cod stocks off Newfoundland.

Influence of climatic changes on the parasites of Atlantic cod Gadus morhua off coastal Labrador, Canada

A study was conducted in 2000 and 2003, following the collapse of the commercial fishery in 1990, to compare metazoan parasites of Atlantic cod Gadus morhua, captured off coastal Labrador, with samples taken in 1980 and 1986. Fish were captured by otter trawl offshore in the North Atlantic Fish Organisation subarea 2J. Parasites were removed from the digestive tract, stained, identified and compared between the different groups. Both the prevalence and mean abundance of trematodes, larval nematodes and E. gadi were significantly lower in fish taken in 2000 and 2003 than in 1980. While mean values of trematodes and nematodes declined in 1986, those of Echinorhynchus gadi remained unchanged in 1986 and 1990. Four-year-old cod sampled in 1990 harboured significantly fewer E. gadi than older age groups. The most commonly occurring trematodes included Podocotylereflexa, Lepidapedon elongatum, Derogenes varicus and Hemiurus levinseni while the larval nematode, Anisakis sp. was predominant. Comparison of offshore samples taken in 2000 and 2003 with others taken in previous years suggests an overall decline of parasites coincident with a change in climatic conditions, the absence of a major food source, namely capelin Mallotus villosus, of cod and ultimately the decline of the Labrador population.

Nematode infestation of fillets from Atlantic cod, Gadus morhua, off eastern Canada

The prevalence and intensity of larval nematodes in fillets of Atlantic cod, Gadus morhua, were examined and compared with similar data from a previous survey conducted about 30 yr ago. Anisakis simplex occurred more often in the nape of the fillet, whereas Pseudoterranova decipiens was the predominant species in napeless fillets. The results suggest an increase in both the prevalence and intensity of P. decipiens in fillets of cod, especially those originating from the Gulf of St. Lawrence and coastal Nova Scotia.