Distribution and abundance of sealworm (&lt;i&gt;Pseudoterranova decipiens&lt;/i&gt;) and other anisakid nematodes in fish and seals in the Gulf of St. Lawrence: potential importance of climatic conditions

David J Marcogliese

doi:10.7557/3.2962

Abstract

Prevalence and abundance of sealworm (Pseudoterranova decipiens) and other anisakid nematodes were determined in a variety of fishes from the Gulf of St. Lawrence in 1990 and 1992. Sealworm abundance and prevalence were also determined in three species of seals in the Gulf between 1988 and 1992. Atlantic cod (Gadus morhua) and shorthorn (Myoxocephalus scorpius) and longhorn sculpin (M. octodecemspinosus) were the fishes most heavily infected with sealworm. Grey seals(Halichoerus grypus) proved to be the most important definitive hosts for sealworm in the Gulf. Abundance of sealworm increased, whereas that of Anisakis simplex and contracaecine nematodes decreased, from north to south in the Gulf. Abundance of sealworm increased compared to earlier surveys in most areas of the Gulf, but decreased in both cod and grey seals during the course of this study. In contrast, abundance of Contracaecum osculatum and Phocascaris spp. in grey seals and cod continued to increase during the study period. Observed increases of nematodes are attributed to growing populations of grey seals (for sealworm) and harp seals (for Contracaecinea). Levels of A. simplex remained relatively constant between 1988 and 1992 in both grey seals and cod. There is no evidence suggesting that observed patterns in nematode abundance were due to changes in grey seal diet. Nor was there any evidence of competition between P. decipiens and C. osculatum in grey seals affecting either sealworm abundance or fecundity. The trends detected herein are attributed to climatic events in the Gulf of St. Lawrence, where water temperatures in the cold intermediate layer consistently decreased between 1986 and 1994. It is suggested that low temperatures inhibited development and hatching of sealworm eggs, but not those of C. osculatum.

Highlights

Sealworm (Pseudoterranova decipiens) is an anisakid nematode found in the flesh of commercially important groundfish such as Atlantic cod (Gadus morhua)
While three sibling species of P. decipiens exist in the North Atlantic, designated A, B, and C (Paggi et al 1991), it is presumed that sealworm from the Gulf of St
Trends in sealworm abundance Typically, with the exception of a sample of Atlantic cod from Anticosti Island in 1990, sealworm abundance is much higher in fish (Templeman et al 1957, McClelland et al 1985, 1987, Boily and Marcogliese 1995, Marcogliese 1995) and seals (Marcogliese et al 1996) from the southern Gulf than from the northern Gulf

Summary

Introduction

Sealworm (Pseudoterranova decipiens) is an anisakid nematode found in the flesh of commercially important groundfish such as Atlantic cod (Gadus morhua). This parasite poses a cosmetic problem for the fishing industry in North Atlantic waters, as its large larvae are visible and distasteful to consumers. Over 60 species are infected in the North Atlantic alone (McClelland et al 1990). While three sibling species of P. decipiens exist in the North Atlantic, designated A, B, and C (Paggi et al 1991), it is presumed that sealworm from the Gulf of St. Lawrence belong to P. decipiens B (see Boily and Marcogliese 1995, Marcogliese et al 1996, Marcogliese, 2001), formally referred to as P. decipiens (sensu stricto) (Paggi et al 2000)

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Conclusion