Abstract
Experimental and natural invertebrate intermediate hosts of sealworm (Pseudoterranova decipiens) as well as transmission experiments of sealworm from invertebrates to fish are reviewed and summarized. Experimental hosts include copepods, mysids, cumaceans, isopods, amphipods, decapods, annelids, and molluscs. Invertebrates collected from eastern Canada between 1989 and 1995 were checked for nematode infections by microscopic examination of dissected animals or enzymatic digestion of bulk samples. Third-stage larval sealworm were found in mysids (Neomysis americana, Mysis stenolepis) from Passamaquoddy Bay, the Bras d’Or Lakes, inshore Cape Breton, Sable Island and Sable Island Bank. Infected amphipods (Amphiporeia virginiana, Americorchestia megalophthalma, Gammarus spp.) were found only on Sable Island. Typical infection rates in macroinvertebrates were 1-4/1000. No sealworm infections were found in approximately 18,000 amphipods examined from Sable Island Bank, the site of the most heavily infected fishes in eastern Canada. In Wallace Lake, a brackish pond on Sable Island, infection rates were much higher in mysids than in amphipods. Estimates of rates of transmission of sealworm from invertebrates to fish were derived from infection levels in Wallace Lake and feeding experiments involving sticklebacks and invertebrate prey. It is concluded that mysids may be much more important than amphipods in transmitting sealworm to fish hosts.
Highlights
Sealworms (Pseudoterranova decipiens) are parasitic nematodes (Anisakidae) whose adults infect stomachs of seals.Eggs are passed with the feces and sink to the bottom at a rate of 1.01 x 10-4 m/s (McConnell et al 1997), where free-living larvae hatch.There is debate over how many moults occur in the egg, and whether an L or an L stage larva hatches (Koie et al 1995, Measures and Hong1995)
Three sibling species designated Pseudoterranova decipiens A, B and C have been found in the North Atlantic, with types B and C occurring in Canadian waters (Paggi et al 1991)
McClelland (1982) successfully infected 12 species of harpacticoid copepods and one cyclopoid with larvae hatched from eggs obtained from gravid female sealworms recovered from harbour and grey seals (Table 1)
Summary
Sealworms (Pseudoterranova decipiens) are parasitic nematodes (Anisakidae) whose adults infect stomachs of seals. Development and hatching are temperature, but not salinity, dependent (Brattey 1990, Measures 1996) These larvae are infective to invertebrates, which transmit the larvae to fish when ingested (McClelland et al 1983). Three sibling species designated Pseudoterranova decipiens A, B and C have been found in the North Atlantic, with types B and C occurring in Canadian waters (Paggi et al 1991). All sealworms recovered from seals and fish off Nova Scotia, Newfoundland, and the Gulf of St. Lawrence are P. decipiens B (Paggi et al 1991, Brattey and Davidson 1996, Brattey and Stenson 1993). Experimental and natural infections of sealworm in invertebrates are reviewed and integrated together with new developments in understanding the sealworm life cycle
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