Distribution of helminths in the digestive tracts of New Zealand freshwater eels

Abstract

The distributions of the nematode parasites Paraquimperia sp., Spirocamallanus sp., and Cucullanus sp. in the intestines and recta of Anguilla dieffenbachii and A. australis from Lake Ellesmere and the South Branch of the Waimakariri River were studied over two years. Peak occurrence of Paraquimperia was in the anterior intestine of A. australis and mid intestine of A. dieffenbachii. Male and female Spirocamallanus sp. established in the mid intestine, but as female worms grew they attached more anteriorly and thus maintained the mid body in the mid intestine, prevented the tail end entering the rectum, and maintained the vulvae close to male worms. Cucullanus sp. was most often found in the mid intestine, but occurred throughout the intestine, possibly because of migration with food. Paraquimperia and Spirocamallanus extended their range with crowding; Cucullanus increased in density in the mid intestine. Posteriad movement, with or without subsequent evacuation, was a general feature of all species in both hosts, held live or examined after death. Chilling and freezing slowed or arrested loss from dead hosts. Larger worms (Spirocamallanus sp.) moved and were lost more rapidly than small worms (Paraquimperia sp.); worm loss was more rapid from A. dieffenbachii than from A. australis.

Distribution of helminths in the digestive tracts of New Zealand freshwater eels

“…The distributions of S. anguiilae and T. opisthorchis were consistent in pattern from eel to eel, but variation did occur in the extension of each species along the tract in relation to the other species in individual eels (Hine 1980a). In single infections, or in concurrent infections in which numbers of one species were low (<10), the distributions were different from those in fish in which both species occurred together in higher numbers (>10) of each species ( Fig.…”

“…The positive association between S. anguiilae and T. opisthorchis may be explained by the similarity of their life cycles (MacFarlane 1952), concurrent infection of hosts at all stages of the life cycle, and consequently concurrent acquisition by the eel definitive host (MacFarlane 1952, Hine 1980a. As well as selective site segregation, with some interactive site segregation in the alimentary tracts of eels, personal observations (P.M.H.)…”

“…Of the 7 out of 297 A. dieffenbachii in which both nematodes occurred concurrently, they did so in the same 10% sector in only two eels. This strong negative association may account for the relative incidence of these nematodes in each host species: Paraquimperia is common in A. australis, but less common in A. dieffenbachii; Spirocamallanus is common in A. dieffenbachii, but rare in A. australis (Rid 1973, Hine 1978, 1980b. Rid (1973) attributed the lack of Paraquimperia in A. dieffenbachii to host food preferences and, because only immature Spirocamallanus were found in A. australis, concluded that it is extending its host range from A. dieffenbachii into A. australis.…”

“…Although both host species occur separately in some habitats, there is overlap in other habitats (Hine 1978). When overlap of host distribution occurs, A. australis maintains the Paraquimperia population so that it is available to crossinfect A. dieffenbachii, should Spirocamallanus be absent from that host.…”

“…Although site segregation by fish helminths is well known (Awachie 1968, MacKenzie & Gibson 1970, Halvorsen & MacDonald 1972, Holmes 1973, Evans 1977, and selective site segregation modified by interactive site segregation of the flukes Stegodexamene anguillae and Telogaster opisthorchis occurs in New Zealand eels (Hine 1980a), temporal segregation is less common (Miller 1943, Cannon 1972. Competitive exclusion by fish helminths has also been recorded (Esch et al 1976), but this term has sometimes been confused with site segregation (Chappell 1969, Amin 1975.…”