Abstract
AIM: This study aimed to evaluate influence of hydrological variation, ontogeny and interspecific variation in the feeding activity and diet composition for P. nattereri and S. marginatus in floodplain of Negro River, South Pantanal. METHODS: The samples were taken with the use of gillnets and cast nets of different sizes, from October/2005 to August/2008. RESULTS: We sampled 748 specimens, 442 of P. nattereri and 306 of S. marginatus. We identified 31 items in the dry and 14 in the flood season for P. nattereri, and 29 items in the dry and eight in the flood season for S. marginatus. For both species, fish was the predominant food item in both seasons. The PERMANOVA results showed that the diet varied significantly between the two species (p<0.001), during ontogenetic development (p<0.001) and seasonally (p=0.024). The ancova results suggests that the intensity of food intake was higher in the dry season (p<0.001) for both species. The niche breadth varied only between studied species with S. marginatus presenting higher niche breadth than P. nattereri. CONCLUSION: Piranhas feed more during dry season, probably because in this period food is more varied and abundant, due to the concentration of fish in the main river channel. There were ontogenetic changes in the diet, with no feeding overlap between the two species, probably because of differences in preference for some items and differences in feeding behavior displayed during hunting attacks.
Highlights
Studies on the feeding of fishes provide important information for a better understanding of the relationships between components of the ichthyofauna and other organisms of the aquatic community, and are an efficient approach to understand community structures (Polis and Winemiller, 1996)
Twenty-nine food items were recorded in the dry season, and eight in the flood for S. marginatus and for P. nattereri, 31 items were recorded in the dry season, and 14 in the flood
Studies in different Brazilian rivers have reported that many piranha species exploit a wide variety of food items, including arthropods, fish, other vertebrates, scales and plant remains (MachadoAllison and Garcia, 1986; Goulding et al, 1988; Sazima and Machado, 1990; Costa et al, 2005), fish is the most preferred (Piorski et al, 2005; Trindade and Jucá-Chagas, 2008)
Summary
Studies on the feeding of fishes provide important information for a better understanding of the relationships between components of the ichthyofauna and other organisms of the aquatic community, and are an efficient approach to understand community structures (Polis and Winemiller, 1996). Knowledge of food sources used by fish may provide insight into the habitat, food availability in the environment and some aspects of behavior, while information about the intensity of food intake may be useful to complement studies of competitive interactions or resource partitioning among species (Schoener, 1974; Hahn et al, 1997). Pygocentrus nattereri Kner, 1858 and Serrasalmus marginatus Valenciennes, 1837 are piranhas, are widely distributed in rivers of the Pantanal, and are the most abundant predators in the Negro River (unpublished data). Both species are of medium size, with a high, strongly compressed body. Piranhas are predators that feed on pieces of fins, scales and other body parts of their prey (Agostinho and Marques, 2001; Pompeu and Godinho, 2003; Costa et al, 2005)
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