Experimental infection of fish with larval sealworm, Pseudotertanova decipiens (Nematoda, Anisakinae), transmitted by amphipods

Abstract

Larval sealworm (Pseudoterranova decipiens, (Krabbe 1878)) were transmitted sequentially through copepods and amphipods to 12 phylogenetically diverse fish species. Although P. decipiens in amphipods were 0.82–7.08 mm long, only those ≥1.41 mm were infective to fish. Sealworm transmitted at 15 °C migrated to the musculature within 6 h in mummichog (Fundulus heteroclitus) and 12 h in rainbow smelt (Osmerus mordax) but were confined to the bolus in an Atlantic cod (Gadus morhua) stomach at 24 h. All sealworm in smelt, but only 12% of those in cod, occupied the musculature after 7 days. Death of 15 mummichog and a grubby (Myoxocephalus aenaeus) 10–20 days after exposure apparently resulted from damage to the brain, heart, aorta, liver, or spleen by feeding and migrating nematodes. Whereas 100% of the sealworm in grubby and 86–88% of those in mummichog and winter flounder (Pleuronectes americanus) were dead and encapsulated in host connective tissue after 56 days, all P. decipiens in smelt were viable and unencapsulated. With length increasing linearly at 0.421 mm day−1, sealworm larvae reached 27.29 (23.60–30.70) mm after 56 days in smelt at 15 °C. However, P. decipiens, which escaped the host tissue response in mummichog and flounder, were only 10.14 (6.00–21.80) and 12.42 (9.53–14.40) mm in length, respectively.

Review of experimental and natural invertebrate hosts of sealworm (<i>Pseudoterranova decipiens</i>) and its distribution and abundance in macroinvertebrates in eastern Canada

“…In a further set of experiments, McClelland (1995) demonstrated that only worms larger than 1.41 mm in length, and usually larger than 2.00 mm, were infective to fish. As sealworms cannot attain this size in microinvertebrate hosts such as copepods, these results imply that macroinvertebrates are an essential component of transmission.…”

Anisakiosis and pseudoterranovosis

“…In addition, associations between the prevalence of sealworm infections in commercial fish and seal populations are not fully understood (McClelland, 2002). Other abiotic factors, such as water temperature, are important in transmission (McClelland, 1982(McClelland, , 1990(McClelland, , 1995Measures, 1996;McClelland and Martell, 2001;McClelland, 2002).…”

“…For example, 12 different species of fish (marine, anadromous, and freshwater) including Atlantic salmon, brook trout, rainbow smelt, and Atlantic cod were susceptible to experimental infections by P. decipiens using experimentally infected amphipod intermediate hosts (McClelland, 1995). In some fish such as rainbow smelt, tissue responses to infections were absent.…”

“…Although Anisakis spp. appear to cause few pathologies in fish-unless the liver is heavily infected or there are large numbers of worms-sealworms can kill small fish, particularly when vital organs are damaged by migrating larvae (McClelland, 1995). Experimental evidence indicates that P. decipiens infection of some fish species affects their ability to swim and thus escape predators (Sprengel and Lüchtenberg, 1991).…”

“…Larvae may or may not be encapsulated and may lie coiled or fully extended in tissues, but this may be a function of host species, temperature, or age of infection (Ramakrishna and Burt, 1991;McClelland, 1995). Pseudoterranova spp.…”