Studies on the alimentary tract helminths of the black swan, Cygnus atratus (Latham)

Abstract

Helminth parasites in the alimentary tract of the Black Swan, Cygnus atratus, are surveyed and considered, together with some aspects of the ecology of the definitive and intermediate hosts. Thirteen helminth species were recovered from 294 Black Swans, comprising the seven cestodes Nematoparataenia paradoxa, Drepanidotaenia lanceolata, D. curiosa, Parabisaccanthes bisacculina, and three Hymenolepis species; the three nematodes Pectinospirura argentata, Amidostomum cygni, and Capillaria ellisi; and the three trematodes Echinostoma revolutum, Cathaemasia sp., and Paramonostomum sp. Three new species of Hymenolepis (Cestoda) are described. The range in measurements of genital organs, and the presence or absence of a pseudoscolex and accessory sacs are noted in the descriptions for the hymenolepid cestodes recovered (Drepanidotaenia and Parabisaccanthes). The life histories of Hymenolepis, Drepanidotaenia and Parabisaccanthes species are examined, and the intermediate host of Drepanidotaenia and Parabisaccanthes is identified for the first time in New Zealand. The trematode and nematode species recovered during this study are described. Other helminth life histories are reviewed and possible New Zealand intermediate hosts are suggested. Quantitative analyses are made of the helminth infections. The distribution of the various species along the alimentary canal is discussed. The level of infection in male and female Black Swans is similar. Cygnets have four helminth species fewer than older swans. The intensity of trematode and nematode infections is highest in the cygnets, and the intensity of cestode species is highest in juvenile swans. The prevalence of cestodes is highest in adult birds. Swans from the two collection sites, Lakes Waikare and Whangape, differed in the intensity of infection by P. argentata and Hymenolepis sp. B, and in the prevalence of D. curiosa. Seasonal fluctuations in infection levels are discussed. All helminths had two seasonal increases in infection levels, except for P. argentata, which had three increases. Interrelationships of the host-parasite environment are discussed in an attempt to explain composition and dynamics of the swan's helminth fauna.