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Excretory/secretory (ES) products are molecules produced by parasitic nematodes, including larval Anisakis simplex, a parasite occurring in numerous marine fish hosts. The effects of these substances on host physiology have not been fully described. The present work elucidates the influence of ES substances on the fish immune system by measuring immune gene expression in spleen and liver of rainbow trout (Oncorhynchus mykiss) injected intraperitoneally with ES products isolated from A. simplex third stage larvae. The overall gene expression profile of exposed fish showed a generalized down-regulation of the immune genes tested, suggesting a role of ES proteins in immunomodulation. We also tested the enzymatic activity of the ES proteins and found that lipase, esterase/lipase, valine and cysteine arylamidases, naphthol-AS-BI-phosphohydrolase and α-galactosidase activities were present in the ES solution. This type of hydrolytic enzyme activity may play a role in nematode penetration of host tissue. In addition, based on the notion that A. simplex ES products may have an immune-depressive effect (by minimizing immune gene expression) it could also be suggested that worm enzymes directly target host immune molecules which would add to a decreased host immune response and increased worm survival.

A significant increase in the infection level of Baltic cod Gadus morhua with the anisakid nematode larvae Contracaecum osculatum and Pseudoterranova decipiens has been recorded during recent years due to the expanding local population of grey seals Halichoerus grypus, which act as final hosts for these parasites. Here, we report from an investigation of 368 cod (total length [TL] 6−49 cm; caught in ICES Subdivision 25) that the infection level of juvenile cod (TL 6−30 cm) with larvae of C. osculatum and P. decipiens is absent or very low, whereas it increases drastically in larger cod (TL 31−48 cm). A third nematode Hysterothylacium aduncum was rarely found. The study indicates that the prey animals for large cod act as transport hosts for the parasite larvae. Analyses of stomach contents of cod caught in the same area (2007−2014) showed that small benthic organisms (including polychaetes Harmothoë sarsi) are preferred food items by small cod, the isopod Saduria entomon is taken by all size classes, and sprat Sprattus sprattus are common prey items for cod larger than 30 cm. Parasitological investigations (microscopic and molecular analyses) of H. sarsi (100 specimens) and S. entomon (40 specimens) did not reveal infection in these invertebrates, but 11.6% of sprat (265 specimens examined) was shown to be infected with 1−8 C. osculatum third stage larvae per fish. Analyses of sprat stomach contents confirmed that copepods and cladocerans are the main food items of sprat. These observations suggest that the C. osculatum life cycle in the Baltic Sea includes grey seals as final hosts, sprat as the first transport host and cod as second transport host. It may be speculated that sprat obtain infection by feeding on copepods and/or cladocerans, which could serve as the first intermediate hosts. One cannot exclude the possibility that the size-dependent C. osculatum infection of cod may contribute (indirectly or directly) to the differential mortality of larger cod (> 38 cm) compared to smaller cod (< 30 cm) recently recorded in the Baltic cod population.

Viability of Cryptocotyle lingua metacercariae from Atlantic cod (Gadus morhua) after exposure to freezing and heating in the temperature range from -80 °C til 100 °C. Food Control, 50,[371][372][373][374][375][376][377] Viability of Cryptocotyle lingua metacercariae from Atlantic cod (Gadus morhua) after exposure to freezing and heating in the temperature range from À80 C to 100 C a b s t r a c tThe presence of parasites in fish products is a problem that concerns consumers and authorities due to the potential hazards it may cause. The majority of studies on the viability of parasites in marine fish products currently focus on nematodes of the family Anisakidae whereas only few are concerned with trematodes. In this study on the heterophyid trematode Cryptocotyle lingua (identified by morphometric and molecular techniques) we isolated metacercariae from Atlantic cod (Gadus morhua) and incubated the parasites in cod muscle tissue at different temperatures ranging from À80 C to 100 C and subsequently tested their viability. SEM images were made to assess the physical damage caused to parasites exposed to different temperatures. Temperatures between 50 C and 100 C and between À80 C and À20 C killed the metacercariae present in fish flesh in less than 2 h. Controls kept at 5 C survived for nine days. Extreme freezing temperatures caused minimal visual physical damage to cysts, but the tegument of metacercariae was severely affected at all temperatures when incubated for long periods.

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