Parasites Are Paramount: Vertical Trophic Positions of Parasitic Catfishes in a Tropical River Food Web

Abstract

The Neotropical catfish family Trichomycteridae contains parasitic fishes that include scale and mucus feeders (subfamily Stegophilinae) and blood feeders (i.e., ‘candirus’, subfamily Vandelliinae). The influence of parasitic catfishes on food web dynamics is unknown. Most ecological information on the feeding ecology of freshwater parasite catfishes has been based on visual observation of diets via stomach contents analysis, a method that does not provide information about the origin of ingested blood or mucus (interspecific interactions) or vertical trophic position of these parasites. We used stable isotope analysis of carbon (d¹³C) and nitrogen (d¹⁵N) to explore the role of parasitic catfishes in a river food web in Guyana, South America. We obtained tissue samples from over 100 fish species, including three genera of trichomycterid parasitic catfishes. Parasitic catfishes were estimated to have the highest trophic positions in the food web, which, given their small size (~5 cm total length), contributed to a weak relationship between trophic position and fish body size for the fish community. Ochmacanthus, a mucus-feeder, had higher d¹⁵N and estimated trophic position than the two blood feeders, Paracanthopoma and Vandellia. Results from stable isotope analysis indicate that parasitic catfishes should be considered among the top consumers in this hyperdiverse fish community.