We examined the distribution and co-occurrence of the exotic digenetic trematode Centrocestus formosanus, its exotic intermediate host the red-rim melania snail Melanoides tuberculatus, and rates of infection of fish in 10 spring systems throughout western Texas during 1999 and 2011. Four of the spring systems (East Sandia Springs, Independence Creek, Big Bend National Park Refugium Pond, and Clear Creek) did not contain red-rim melania snails in 1999 and 2011. Four spring systems that were populated with snails (San Felipe Creek, San Solomon Springs, Phantom Lake, and Diamond Y Springs) contained the trematode and were positive for branchial infection in fish except Diamond Y Springs which contained uninfected snails and fish. Since 1999, two additional spring systems, Pinto Creek and Devils River, contained the trematode. We found a high prevalence of branchial infection for fish collected regardless of species. Seventeen of the 21 species of fish collected from the spring systems were positive for infection by trematodes. On average, the most infected genera were Micropterus and Lepomis followed in decreasing order by Etheostoma, Dionda, Astyanax, Cichlasoma, Notropis, Cyprinella, Gambusia, Ictalurus, and Hypostomus. Seven state-listed or federally listed species we collected had a relatively high percentage (mean = 52%) of developing metacercarial cysts except E. grahami (mean = 14%). Our laboratory study suggests that, for Gambusia, rates of infection by trematodes are species–specific with G. affinis having significantly more cysts than did G. nobilis and G. gaigei. Our work extended the documented range of red-rim melania snails and C. formosanus in Texas.
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Vol. 59 • No. 2