This study analyzed the structure of the gill rakers of Parapimelodus valenciennis and Parapimelodus nigribarbis (planktivorous), Serrasalmus maculatus and Hoplias malabaricus (piscivorous), Iheringichthys labrosus (benthophagous) and Hypostomus commersonii (detritivorous) and related it with the body size and feeding habits of these species. The species of Parapimelodus and H. commersonii showed long, filiform and closely spaced gill rakers, similar to those of species that use the gill rakers as a filter to assist in the retention of small particles. The widely spaced gill rakers of I. labrosus probably allow the retention of insect larvae, but not particles of inorganic matter. In H. malabaricus and S. maculatus the gill rakers are most likely related to prey capture and swallowing, as observed in other piscivorous species. In general, gill raker length and the distance between gill rakers have a positive relationship with fish length. The gill rakers show adaptations related to the diet of the fish, but morphological variation may occur even between species whose feeding habits are the same.
filtering; gill arches; feeding behavior
