Surveys of larval sealworm (&lt;i&gt;Pseudoterranova decipiens&lt;/i&gt;) infection in various fish species sampled from Nova Scotian waters between 1988 and 1996, with an assessment of examination procedures

G Mcclelland,Dj Martell

doi:10.7557/3.2959

Abstract

Between November 1988 and October 1996, >10,000 fish from the Breton Shelf, Sable Island Bank and the northeastern Gulf of Maine were examined for larval anisakines. Larval sealworm, Pseudoterranova decipiens, occurred in 30 of 39 species surveyed, including 8 new host records, Enchelyopus cimbrius, Lycodes reticulatus, Eumesogrammus praecisus, Lumpenus lumpretaeformis, Lumpenus maculatus, Cryptacanthodes maculatus, Artediellus atlanticus and Triglops murrayi. The parasite was most prevalent and abundant in mature demersal piscivores and benthic consumers. Sealworm densities (nr kg-1 host wt.), however, were greatest in small benthophagous fish including mature E. cimbrius, A. atlanticus, T. murrayi and Aspidophoroides monopterygius, and juvenile Hippoglossoides platessoides. ANOVA revealed that geographical disparities in sealworm prevalence and abundance were highly significant in 14 of 20 species tested, although significant disparities between samples from each of the three areas were evident only in H. platessoides. Almost invariably, infection parameters were greatest in fish from Sable Island Bank. ANOVA also indicated that sealworm prevalence and/or abundance increased significantly in Sable Island Bank populations of Gadus morhua, H. platessoides, and seven other species between 1985-1986 and 1989-1990. Routine examinations, in which host flesh was sliced and candled, proved as efficacious as digestion in warm (35° C) pepsin-HCl for detection of larval sealworm in the flesh of large frozen fish. Procedures employing fresh (iced) samples, digestion at ambient temperature and microscopy are recommended, however, for surveys of small benthic consumers. Many of the sealworm infecting the latter hosts are tiny (2 to 10 mm in length) nematodes, which escape detection by routine inspection, and may not survive in warm pepsin-HCl solution.

Highlights

As they lack direct economic significance, small benthophagous fish, which include the juveniles of commercially important demersal species as well as underutilised species, are often overlooked as potential reservoirs of Pseudoterranova decipiens larvae
All fish from the Breton Shelf and Gulf of Maine, and the majority of those from Sable Island Bank were sampled between February 1989 and October 1990
Additional specimens of benthic consumers such as fourbeard rockling, Vahl’s eelpout, snakeblenny (Lumpenus lumpretaeformis), wrymouth (Cryptacanthodes maculatus), hookear and mailed sculpin, alligatorfish and spiny lumpsucker were collected from Sable Island Bank between October 1991 and August 1993

Summary

Introduction

As they lack direct economic significance, small benthophagous fish, which include the juveniles of commercially important demersal species as well as underutilised species, are often overlooked as potential reservoirs of Pseudoterranova decipiens larvae. Recent field and laboratory studies have shown, that they may be essential in the transmission of sealworm to larger, commercially exploited fish, if not directly to definitive (seal) hosts (McClelland 1995). In an earlier survey of Sable Island Bank on the central Scotian Shelf (McClelland et al 1990), larval sealworm were found in 26 of 32 marine fish species. While it was most prevalent and abundant in large demersal piscivores, P. decipiens often occurred in greatest density (nr/unit host weight) in small (juvenile and mature) benthic consumers (Fig. 1). It was apparent that sealworm larvae recently transmitted to these hosts would be considerably smaller than those detected by candling procedures typically employed in seal-

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