The Predominant Definitive Avian Hosts of the Invasive Asian trematode, Centrocestus formosanus, in the Headwaters of the Comal, San Antonio, and San Marcos Rivers of Central Texas
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Centrocestus formosanus is a heterophyid trematode of Asian origin that encysts as a metacercaria in the gills of many fishes, and presumably uses local piscivorous birds as definitive hosts. It has been reported to be a serious pathogen of the endangered fountain darter, Etheostomafonticola, in the Comal River (Comal County, Texas). The gills of the darters can be so extensively damaged by this trematode that the worm threatens the survival of the fish in its habitat during low-water conditions. The research objectives were to determine the predominant definitive host of C. formosanus, particularly in the Comal River, and to recover and identify other helminths encountered in the digestive system of the birds during necropsy.
Twelve species of migratory piscivorous birds were collected and examined for adult worms. The birds were collected from three aquatic habitats between San Marcos and San Antonio, inclusively, all of which are dominated by water from the Edwards Aquifer. All birds were then transported on ice to the lab and immediately dissected. The entire digestive tract of the birds was excised, slit longitudinally, and examined briefly for helminths. Specimens found live were fixed using taxon-specific protocols. The intestine and its contents were examined under a dissecting microscope for helminths, with adults of C. formosanus being the focus of the search.
Based on presence/absence of adult Centrocestus, the avian species that was designated as the predominant definitive host for the parasite in the study area is the Green Heron (Butorides virescens). Of the ten Green Herons collected, two were heavily infected with heterophyid trematodes, some of which were identified as Centrocestus sp. No evidence was found that any of the other eleven avian species might be important definitive hosts for C. formosanus in the study area. Other parasites recovered during the necropsies included several species each of Trematoda, Nematoda, Cestoda, one species of Acanthocephala, and one species of Giardia.
CitationKuhlman, T. A. (2007). The predominant definitive avian hosts of the invasive Asian trematode, Centrocestus formosanus, in the headwaters of the Comal, San Antonio, and San Marcos rivers of Central Texas (Unpublished thesis). Texas State University-San Marcos, San Marcos, Texas.
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