Seasonal changes in the infection of young saithe, Pollachius virens, with Anisakis simplex and other helminths: Árstíðarbroytingar í rundorma-infektión í seiði

Abstract

Samples of saithe, Pollachius virens, were taken approximately every second month, from Jan to Dec 1996. A total of 458 saithe (age 1-2 years and 3 singles 3 years old) were examined by pepsin-digestion and dissection for nematodes in the fillets and the viscera. For the 1- year old saithe the prevalence of infection in fillets and viscera of Anisakis simplex third stage larvae was increasing with time (from 40 % in May to 71 % in Dec). For the 2-year old the figures ranged from 18 % Jan, to 84 % in October (80 % in December), indicating an increase in infection with age and different levels between different age classes. The intensity of infection was increasing with time for the 1-year old, but appeared stable for the 2-year old. Similar patterns were observed for the intensity and prevalence of infection of saithe with third stage larvae of Pseudoterranova decipiens and Contracaecum sp., but the figures were generally lower than for A. simplex. The predominantly encapsulated nematodes Anisakis, Pseudoterranova and Contracaecum had almost fixed ratios among themselves, which reflects their stable environment. Other parasites found in the viscera were the nematodes Hysterothylacium aduncum (larvae and adults), Cucculanus sp. and the acanthocehpalean Echinorhynchus gadi. They exhibited a more complex and varying pattern of abundance and prevalence of infection, reflecting their unstable environment primarily in the gut lumen. A single record was made of the crustacean Clavella sp. (Laernoidea) and an unidentified plerocercoid of a cestode. The changes of the Anwafa'í-infectiorJ in saithe seem to have an inverse relationship with the changes of the primary production.