A parasitological survey of the American lobster Homarus americanus from the Northumberland Strait, southern Gulf of St. Lawrence

Abstract

A parasitological survey was conducted on 233 lobsters from the Northumberland Strait. Routine macroscopic and histological examinations revealed that 93% were infected by one or more parasites. Parasites detected included a Spiruroidean nematode believed to belong to the genus Ascarophis, an unidentified flagellate, the annelid Histriobdella homari, and the sporozoan Porospora gigantea. The latter organism was by far the most common. Highest parasite frequencies occurred in lobsters whose carapace measurements exceeded 50 mm.

Pathogens, Parasites and Other Symbionts

“…Boghen (1978) found differences in prevalence in relation to size, with small juveniles (<50 mm CL) having a lower prevalence than larger juveniles and adults (>50 mm CL). This is likely to be due to a change in the diet of the larger juveniles, which are capable of handling larger molluscan prey.…”

“…It has also been reported from H. americanus off Nova Scotia where its prevalence was extremely low (0.6%) (Montreuil, 1954; and New England (1-2%) (Nickerson, 1894;Herrick, 1909), but not the Gulf of St Lawrence (Boghen, 1978) nor the Mid-Atlantic Bight (Van Engel, 1986). In N. norvegicus, prevalence is positively correlated with host size; lobsters <30 mm CL were not infected (Symonds, 1972).…”

“…Simon (1968) reported 100% prevalence on 27 lobsters examined off Woods Hole, Massachusetts. Boghen (1978) reported a low 11% prevalence from Northumberland Strait. Van Engel et al (1986) found only one specimen of H. homari from their survey of 218 lobsters from the Mid-Atlantic Bight.…”

“…Two species have been reported from the mid-and hindguts of lobsters. Porospora gigantea infects H. americanus (Montreuil, 1954;Théodoridès & Laird, 1970;Boghen, 1978; and H. gammarus (Théodor-idès, 1962), which at least in Europe uses Trochocochlea mutabilis as an intermediate host (Hatt, 1928), and P. nephropis infects N. nephrops (Leger & Duboscq, 1915;Tuzet & Ormières, 1961). Within the lobster, the characteristic trophonts can be found free in the lumen of the mid-and hindguts with their epimeres attached to the gut wall.…”

“…Off Nova Scotia, its prevalence has ranged from 43.6% to 84.2% ; in the Northumberland Straits, prevalence was >80% in juvenile and adult lobsters (>50 mm CL) (Boghen, 1978); and off the Magdalene Islands it reached a prevalence of 100% (Montreuil, 1954). However, it was absent from lobsters sampled in the MidAtlantic Bight (Van Engel et al, 1986), which may indicate the absence of a suitable molluscan intermediate host.…”