Increasing intensities of Anisakis simplex third-stage larvae (L3) in Atlantic salmon of coastal waters of Scotland

Alexander J Kent,Robert A Briers,Karen Diele,Campbell C Pert,Sonja Rueckert

doi:10.1186/s13071-020-3942-5

Alexander J Kent, Robert A Briers + Show 3 more

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https://doi.org/10.1186/s13071-020-3942-5

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Abstract

BackgroundRed Vent Syndrome (RVS), a haemorrhagic inflammation of the vent region in Atlantic salmon, is associated with high abundance of Anisakis simplex (s.s.) third-stage larvae (L3) in the vent region. Despite evidence suggesting that increasing A. simplex (s.s.) intensity is a causative factor in RVS aetiology, the definitive cause remains unclear.MethodsA total of 117 Atlantic salmon were sampled from commercial fisheries on the East, West, and North coasts of Scotland and examined for ascaridoid parasites. Genetic identification of a subsample of Anisakis larvae was performed using the internal transcribed spacer (ITS) region of ribosomal DNA. To assess the extent of differentiation of feeding grounds and dietary composition, stable isotope analysis of carbon and nitrogen was carried out on Atlantic salmon muscle tissue.ResultsIn the present study, the obtained ITS rDNA sequences matched A. simplex (s.s.) sequences deposited in GenBank at 99–100%. Not all isolated larvae (n = 30,406) were genetically identified. Therefore, the morphotype found in this study is referred to as A. simplex (sensu lato). Anisakis simplex (s.l.) was the most prevalent (100%) nematode with the highest mean intensity (259.9 ± 197.3), in comparison to Hysterothylacium aduncum (66.7%, 6.4 ± 10.2) and Pseudoterranova decipiens (s.l.) (14.5%, 1.4 ± 0.6). The mean intensity of A. simplex (s.l.) represents a four-fold increase compared to published data (63.6 ± 31.9) from salmon captured in Scotland in 2009. Significant positive correlations between A. simplex (s.l.) larvae intensities from the body and the vent suggest that they play a role in the emergence of RVS. The lack of a significant variation in stable isotope ratios of Atlantic salmon indicates that diet or feeding ground are not driving regional differences in A. simplex (s.l.) intensities.ConclusionsThis paper presents the most recent survey for ascaridoid parasites of wild Atlantic salmon from three coastal regions in Scotland. A significant rise in A. simplex (s.l.) intensity could potentially increase both natural mortality rates of Atlantic salmon and possible risks for salmon consumers due to the known zoonotic role of A. simplex (s.s.) and A. pegreffii within the A. simplex (s.l.) species complex.

Highlights

Red Vent Syndrome (RVS), a haemorrhagic inflammation of the vent region in Atlantic salmon, is associated with high abundance of Anisakis simplex (s.s.) third-stage larvae (L3) in the vent region
36,563 Ascaridoidea larvae were collected from 117 Atlantic salmon
Prevalence and intensity parameters of all three anisakid nematodes recovered in Atlantic salmon are summarised in Table 1 and Table 2

Summary

Introduction

Red Vent Syndrome (RVS), a haemorrhagic inflammation of the vent region in Atlantic salmon, is associated with high abundance of Anisakis simplex (s.s.) third-stage larvae (L3) in the vent region. The nomenclature of species belonging to the genus Anisakis has been controversial [2]. There are four clades of sibling species within the genus Anisakis that have been widely accepted. Clade 1, known as the A. simplex (sensu lato) complex, consists of A. berlandi Mattiucci, Cipriani, Webb, Paoletti, Marcer, Bellisario, Gibson & Nascetti, 2014, A. pegreffii Campana-Rouget & Biocca, 1955, and A. simplex (Rudolphi, 1809) (sensu stricto). Clade 2 is formed by A. ziphidarum Paggi, Nascetti, Webb, Mattiucci, Cianchi & Bullini, 1998 and A. nascettii Mattiucci, Paoletti & Webb, 2009. Clade 3 is comprised of A. physeteris (Baylis, 1923), A. brevispiculata Dollfus, 1966 and A. paggiae Mattiucci, Nascetti, Dailey, Webb, Barros, Cianchi & Bullini, 2005, and Clade 4 contains A. typica (Diesing, 1860) Baylis 1920 [2]. Further genotypes Anisakis sp. 1 and Anisakis sp. 2 have been recognised and these show phylogenetic similarities to A. typica and A. physeteris, respectively; additional molecular genetic analyses are needed to fully clarify their taxonomic status [2]

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