Variations in abundance of intestinal helminths of gadwalls (Anas Strepera), mottled ducks (Anas fulvigula) and ring-necked ducks (Aythya collaris) wintering in eastern Texas

Abstract

Free-ranging anatids were collected during the winters of 1990 through 1992 in Freestone, Chambers and Jefferson Counties, Texas. Intestines from 62 gadwalls (Anas Strepera), 13 mottled ducks (Anas fulvigula) and 13 ring- necked ducks (Aythya collaris) were examined for endohelminths. There was no significant difference in total endohelminth abundance between male and female, or juvenile and adult ducks, nor a significant correlation between body weight and parasite load. Parasite diversity decreased through the winter, predominatly due to the increase in abundance of the genus Microsomacanthus. The highest relative density of helminth species occurred in the duodenum and cecae of the hosts. Only one helminth species (Cloacataenia megalops) was found in the cloaca. Twenty-one helminth species, including four genera and six species of Cestoda, one genus and seven species of Digenea, one species of Acanthocephala, and two species of Nematoda, were found. There were also unidentified pseudophylideans. The resident mottled duck was host to more endoheiminth genera than either the gadwall or ring-necked duck, including C. megalops, Diorchis spp., Dicronataenia coronula, Fimbriaria fasciolaris, Microsomacanthus sp. 1 and sp. 2, Sobolevicanthus filumferens, and a pseudophylidean (cestode); Cotylurus flabelliformes, Echinoparyphium flexum, Echinostoma revolutum, Notocotylurus attenuatus, Psilochasmus oxyurus, Psilotrema sp., Zygocotyle lunata (digenean); P. obtusus (acanthocephalan); Trichostrongulus tenuis and Ascaridia gaffl (nematode). Gadwalls were host to C. megalops, Diorchis spp., Hamatolepis teresoides, Microsomacanthus sp. 1 and sp. 2, a pseudophylidean (cestode); Apetemon gracilis, C. flabelliformes, E flexum, E revolutum, N. attenuatus, P. oxyurus, Z lunata (digenean); P. obtusus ; and T tenuis. Ring-necked ducks were host to C. megalops, Diploposthe laevis, Diorchis spp., F fasciolaris, Microsomacanthus sp. 1 and sp. 2, (cestode); C. flabelliformes, E flexum, E revolutum, P. oxyurus, Z lunata; and P. obtusus. In gadwalls, total endohelminth abundance increased from 75 in early winter (October-December) to 395 in late winter (January- April) (p = 0.01 1). Most of this increase is attributed to the genus Microsomacanthus. Polymorphus obtusus abundance increased from 0.5 in early winter to 5.0 in late winter (p 0.034); but most parasites did not exhibit a significant change in abundance through the winter. Zygocotyle lunata prevalence decreased through the winter.