Diet seasonality and resource partitioning by large catfishes in the Madeira River, Brazil

ABSTRACT Large catfishes form a diverse group with complex life histories, different habitat requirements and home range sizes, which may be related to several ecological aspects. Being among the main top predators in Amazonian river channels, they play a critical role in trophic dynamics, making their conservation particularly significant. However, our ecological understanding of this group remains limited. We evaluated the trophic seasonality and interspecific relationships among large pimelodid catfishes with different life histories and habitat uses in the Madeira River, in the Brazilian Amazon. The dataset was compiled through collaboration with local communities and commercial fishermen at 15 fishing sites, with samplings conducted between April 2009 and September 2011. A total of 225 stomachs contained food items that were identified at the taxonomic level of family. The diet was described for eight species, of which diet seasonality was tested for four, while diet dissimilarity and overlap were estimated for seven regarding only the low-water season. The large pimelodids fed upon many fish families. Most Brachyplatystoma species did not exhibit seasonal shifts in prey consumption. Diet overlap was higher among congeneric and channel-restricted species, particularly Brachyplatystoma platynemum, B. rousseauxii, and B. vaillantii. Despite the diet overlap, some degree of trophic niche partitioning was observed, even among channel-restricted Brachyplatystoma species, mainly when comparing B. filamentosum to the other congeneric species.