Spatial and Temporal Variation of Centrocestus formosanus in River Water and Endangered Fountain Darters (Etheostoma fonticola) in the Comal River, Texas




Cantu, Valentin

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Spatial and temporal variations are commonly observed in parasite populations. However, factors that regulate these variations remain unclear. Temperature has been considered an important factor influencing variations in trematode populations, however in a constant thermal ecosystem such as the Comal River, Hays County, Texas, other factors such as variations in hydrology may play a more important role. Populations of Centrocestus formosanus were collected quarterly from river water, and in caged and resident fountain darters from 8 different sites of the Comal River for a year to determine the spatio-temporal patterns of C. formosanus. The hypothesis that current velocity influences the spatial and temporal variation of C. formosanus was also tested. Overall, my results showed C. formosanus cercariae and infections occur year-round in the Comal River. While seasonal variation was not pronounced due to relatively constant temperatures, seasonal abundances of the C. formosanus population slightly increased during the summer and spring. Heterogeneity of current velocities among the sites possibly influenced the spatial variations of C. formosanus at the Comal River. Although spatial and temporal variations in trematode populations may be influenced by current velocities at the Comal River, other factors such as water volume, photoperiod, and recruitment processes initiated by definitive hosts also may play an important role in structuring the trematode population. In this study, cercariometry was a stronger predictor of infections in caged fish than in resident fish. Considering the accuracy of cercariometry, reduced amount of time, labor, and cost, cercariometry may be the most practical field technique to predict spatial and temporal variations of C. formosanus at the Comal River.



etheostoma, trematoda, parasites, Texas


Cantu, V. (2003). Spatial and temporal variation of Centrocestus formosanus in river water and endangered fountain darters (Etheostoma fonticola) in the Comal River, Texas (Unpublished thesis). Texas State University-San Marcos, San Marcos, Texas.


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