The river flood pulse, benthic biofilm, and the nutrition of Prochilodus lineatus

Prochilodus lineatus (Valenciennes, 1837) is one of 270 fish species in the Rio Paraná system yet it comprises \u3e 50% of the fish biomass and is the only fish species in the system known to feed entirely on flocculent benthic biofilm. We studied the feeding behavior and diet of P. lineatus, and the composition of benthic biofilm in river channels, the moving littoral, and in isolated floodplain lakes at different stages of the Rio Paraná hydrological cycle. Prochilodus lineatus selectively ingests hydrolysis-labile-organic-matter rich in amino acids while selectively rejecting mineral matter and refractory organic matter. Assessed in terms of g AA assimilated · kJ−1 energy assimilated, the quality of food ingested by P. lineatus ranges from a maintenance level of 5 to 12 mg AA · kJ−1, a level expected to produce near maximum growth. The level of amino acids in benthic biofilm is highest in shallow waters during the advancing flood (the moving littoral), and P. lineatus have been observed to feed in littoral areas so shallow that their dorsal fins and backs are exposed. Feeding intensity increases with river height as the moving littoral expands. Feeding site selection, selective ingestion, and conditional feeding intensity each increase amino acid assimilation and together constitute a trophic strategy that allows P. lineatus to dominate the fish community of the Rio Paraná