The relationship between ontogenetic variation of intestine length and feeding habits of five stream-dwelling fish species from the Ubatiba River were investigated. Analysed data were based on two size categories (juveniles and adults) and two food categories (animal and vegetal). Diet composition of each size category revealed that Astyanax janeiroensis and Geophagus brasiliensis changed food preference throughout ontogeny and switched from omnivorous/carnivorous to omnivorous/herbivorous and

more »

... rom omnivorous/carnivorous to omnivorous, respectively. These changes were followed by ontogenetic changes in the Intestinal Coefficient (IC). No ontogenetic differences were registered for IC and food categories consumed by Hoplias malabaricus but significant differences in the size of consumed preys as well as positive correlation between fish size (predator) and prey size was observed. Food items (within animal category) consumed by the adult Pimelodella lateristriga were mainly based on allochthonous arthropods whereas juvenile individuals fed with the same intensity on allochthonous and autochthonous arthropods; both juveniles and adult individuals of Mimagoniates microlepis were mainly allochthonous feeders. Mean IC values of Pimelodella lateristriga and Mimagoniates microlepis did not change along body growth. Although changes in food category consumption were not common among all the studied species, changes in the resource exploitation strategy was a rule among them, except for Mimagoniates microlepis.