Spatial and seasonal changes in the diet of Oligosarcus hepsetus (Characiformes, Characidae) in a Brazilian Reservoir

Abstract

We assessed spatial and seasonal changes in the diet of Oligosarcus hepsetus in order to describe the strategy developed by this species that allows their very high abundance in Lajes reservoir, Rio de Janeiro, Brazil. Fish samplings were carried out using gill nets, deployed during ca. 12 and 24 hours, between April 2001 and May 2002. A total of 289 individuals were examined, of which 97 showed gut contents. We used the index of relative importance (IRI) to compare probable dietary shifts, and the frequency of occurrence (% OC) to analyze possible ontogenetic influences on feeding. O. hepsetus showed carnivorous habits, feeding preferably on fish and insects, the latter of which occurred in 71.0% of the guts presenting contents. O. hepsetus consumed different items along the three reservoir zones: insects (61.0% IRI) and Cichla monoculus (38.9% IRI) in the lower zone; Lepidoptera (57.0% IRI) in the middle zone; and C. monoculus (77.0% IRI) in the upper zone. Food items changed seasonally with C. monoculus predominating in autumn 2001, and Hymenoptera and Lepidoptera in the winter. In spring almost all food was Lepidoptera (99.8% IRI), while in the summer Hemiptera dominated in the diet. In autumn 2002 Hemiptera (97.0% IRI) was dominant, in significant contrast with the previous autumn. Individuals smaller than 190 mm SL fed heavily on insects, while fishes predominated in the diet of individuals larger than 190 mm SL. Shifts in prey-capture ability among length classes suggest decreasing intraspecific competition. A higher food plasticity seems to be the strategy employed by this opportunist species, which used food resources available in the reservoir.Key words: food habit, diet, Characiforms, reservoirs. RESUMO

Feeding of Oligosarcus hepsetus (Cuvier, 1829) (Characiformes) in the Serra do Mar State Park - Santa Virgínia Unit, São Paulo, Brazil

“…The Alimentary Preference Degree for the items consumed by Oligosarcus hepsetus showed that the items were occasional, and when these were grouped, the first three items were secondary: Insects (nymphs and pupas); Insects (adults) and Fish. This result was confirmed by Araújo et al (2005) in Lajes Reservoir, where Oligosarcus hepsetus showed a carnivorous feeding habit, feeding only on insects and fish and varying its diet according to the seasons and the zones of the reservoir.…”

“…Hahn et al (2000) found only fish in the stomachs of individuals of Acestrorhyncus lacustris over 10 cm long in the Itaipu Reservoir. Araújo et al (2005) observed a similar situation, in which Oligosarcus hepsetus larger than 19 cm fed principally on fish, in contrast to smaller individuals which fed principally on insects. Similarly, Gealh and Hahn (1998) found for Oligosarcus longirostris in the Segredo Reservoir, that smaller individuals fed on insects, crustaceans and fish, whereas larger ones (>16 cm) were exclusively piscivorous.…”

“…Similarly, Gealh and Hahn (1998) found for Oligosarcus longirostris in the Segredo Reservoir, that smaller individuals fed on insects, crustaceans and fish, whereas larger ones (>16 cm) were exclusively piscivorous. Araújo et al (2005) reported that larger Oligosarcus hepsetus were apparently able to capture higher-quality prey, i.e., which was larger, heavier and probably richer in energy. The increase in size is related to morphological changes (size of buccal aperture and swimming speed) that may facilitate catching fish.…”

“…The cachorro-magro, Oligosarcus hepsetus, is a small to medium-sized carnivore, occurring widely in most of the freshwater ecosystems in southeastern Brazil. It mainly inhabits shallow, densely vegetated microhabitats in small streams or along the banks of larger rivers (Araújo et al, 2005).…”

Population structure, condition and diet of Oligosarcus paranensis (Menezes & Gery, 1983) (Osteichthyes: Characidae) at two reservoirs in South Brazil

“…Oligosarcus has also been recorded in reservoirs (Castro 1996, Gealh & Hahn 1998, Araújo et al 2005, Luz-Agostinho et al 2006, Terra & Araújo 2011, and, in the specific case of O. paranensis, ichthyofaunal suveys have reported its occurrence in the Atibainha, Cachoeira, Taiaçupeba and Itupararanga Reservoirs in the State of São Paulo (Castro & Arcifa 1987, Smith & Petrere Junior 2008 and at Fiú, Mourão, Capivari and Rio dos Patos Reservoirs in the State of Paraná (Luiz et al 2003). The abundance of this species varied among those ecosystems; however, at Fiú and Mourão, O. paranensis stood out during captures (the most and the second most abundant species, respectively).…”