2 research outputs found
Infection levels and species diversity of ascaridoid nematodes in Atlantic cod, Gadus morhua, are correlated with geographic area and fish size
Atlantic cod (Gadus morhua) is among the most important commercial fish species on the world market. Its
infection by ascaridoid nematodes has long been known, Pseudoterranova even being named cod worm. In the
present study, 755 individuals were sampled in the Barents, Baltic and North Seas during 2012–2014.
Prevalences for Anisakis in whole fish and in fillets in the different fishing areas varied from 16 to 100% and
from 12 to 90% respectively. Abundance was also greatly influenced by the sampling area. Generalized additive
model results indicate higher numbers of Anisakis in the North Sea, even after the larger body size was accounted
for. Numbers and prevalence of Anisakis were positively related to fish length or weight. The prevalence of
parasites in whole fish and in fillets was also influenced by the season, with the spring displaying a peak for the
prevalence in whole fish and, at the same time, a drop for the prevalence in fillets. Whereas 46% of cod had
Anisakis larvae in their fillets, the majority (39%) had parasites mainly in the ventral part of the fillet and only
12% had parasites in their dorsal part. This observation is of importance for the processing of the fish. Indeed,
the trimming of the ventral part of the cod fillet would allow the almost total elimination of ascaridoids except
for cod from the Baltic Sea where there was no difference between the dorsal and the ventral part.
The presence of other ascaridoid genera was also noticeable in some areas. For Pseudoterranova, the highest
prevalence (45%) in whole fish was observed in the Northern North Sea, whereas the other areas had prevalences between 3 and 16%. Contracaecum was present in every commercial size cod sampled in the Baltic Sea
with an intensity of up to 96 worms but no Contracaecum was isolated from the Central North Sea. Non-zoonotic
Hysterothylacium was absent from the Baltic Sea but with a prevalence of 83% in the Barents and the Northern
North Sea.
A subsample of worms was identified with genetic-molecular tools and assigned to the species A. simplex (s.s.),
A. pegreffii, P. decipiens (s.s.), P. krabbei, C. osculatum and H. aduncum. In addition to high prevalence and
abundance values, the cod sampled in this study presented a diversity of ascaridoid nematodes with a majority of
fish displaying a co-infection. Out of 295 whole infected fish, 269 were co-infected by at least 2 genera