Downstream Spread of the Digenetic Trematode Centrocestus Formosanus, into the Guadalupe River, Texas




Fleming, Byron P.

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An exotic heterophyid trematode, Centrocestus formosanus, was recently determined to have adverse effects on fishes in the Comal River, a tributary of the Guadalupe River. This prompted an investigation to determine if the parasite and its obligate first intermediate host, Melanoides tuberculata, a gastropod snail, was established in the Guadalupe River. O f the 22 species and 529 fish collected, 50 % of the species (n = 11) and 29 % (n = 152) of the individuals were infected between 28 May 2001 and 09 March 2002. The highest single intensity observed was 656 metacercarial cysts in Notropis amabilis. Among the infected species, prevalence ranged from 16-100%, mean intensities ranged from 46-616 cysts per fish, and relative densities ranged from 9-616 cysts per fish. In addition M. tuberculata were not collected at any site during the course of this one-year study. This prompted a series of fish-cage studies in order to isolate the source of cercariae that infected Guadalupe River fishes. Mean intensity of cysts in blacktail shiners Cyprinella venusta showed a consistent decrease in the Guadalupe River as cages were placed increasingly further downstream from the Comal River and Guadalupe River confluence. However, no infection was observed in caged fish in the Guadalupe River upstream from the confluence. The results of the cage studies and the lack of snails in the Guadalupe River indicate that fish were infected with cercariae released from snails upstream in the Comal River.



trematoda, snails as carriers of disease, Guadalupe River, Comal River


Fleming, B. P. (2002). Downstream spread of the digenetic trematode Centrocestus formosanus, into the Guadalupe River, Texas (Unpublished thesis). Southwest Texas State University, San Marcos, Texas.


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