Trophic ecology of a nonnative population of suckermouth catfish (Hypostomus plecostomus) in a central Texas spring-fed stream

Introduced suckermouth catfishes (Family Loricariidae) are now established in a number of spring-influenced streams in North America but their impacts on native biota are not well documented. Purposes of this study were to quantify gut contents of the loricariid Hypostomus plecostomus from the San Marcos River in central Texas and to evaluate the role of H. plecostomus in the San Marcos River food web using stable isotope analysis. Gut content analysis indicated that H. plecostomus (N = 36) primarily consumed amorphous detritus (87% in biovolume), filamentous red algae (5.4%), and picoplankton (4.1%). Macrophytes, macroinvertebrates, and fish eggs were not found in gut contents. Stable isotopes demonstrate that H. plecostomus occupies a trophic position indicative of an herbivore and likely utilizes detritus of algal origin. The results from our study suggest that large populations of H. plecostomus in the San Marcos River may directly compete with several native herbivorous fishes and may be disrupting trophic flows and nutrient cycling in spring-influenced streams of central and west Texas.