With the purpose of determining the principal food resources responsible for maintaining the fishery yield in a section of the São Francisco River, 6 sampling of the fish fauna were made downstream from the Três Marias Dam, from September 1996 to July 1997. A total of 1,127 individuals of 35 species were captured, using gillnets with mesh sizes varying from 3 to 16 cm. The stomach contents of 33 species were examined in order to determine their diets. Five trophic guilds were established, in the following order of importance: ilyophagous, herbivorous, piscivorous, terrestrial invertebrates feeders, and aquatic invertebrates feeders. The resources sustaining the fish fauna were mainly of allochthonous origin. The ichthyonenosis appears to be mainly dependent on the detritus chain. The ciliary forest and seasonal flooding pulses are the main suppliers of food for the fish fauna.
This study aimed to identify shifts in the Serrasalmus brandtii Lütken, 1875 diet related to body size. Specimens were collected from April 1992 to January 1993 at the Cajuru Reservoir, in the Pará River, São Francisco River Basin, by seining the shore with nets of nylon, 1 mm opening, and with gill nets. Stomach contents of 152 individuals measuring 15-192 mm SL were examined. Food items were identified and weighed separately. For qualitative analysis, the frequency of occurrence method was used. The relative importance of each food component was determined based on the alimentary index (IA i ). The frequencies of occurrence data were subjected to cluster analysis using the Canberra coefficient of dissimilarity and UPGMA as the cluster method. Distinctive gradual changes in food habits, associated with body size, were identified in this species. The smaller individuals fed predominantly on microcrustaceans and insect larvae. The intermediate size classes ingested insects, fish fins, fish scales, and chunks of fish flesh, in this order of importance. For the larger pirambebas, fish was the most abundant food category identified, followed by insects.Key words: Serrasalmus brandtii, body size, trophic ecology, reservoir, similarity. RESUMOModificações na dieta da pirambeba Serrasalmus brandtii Lütken, 1875 (Osteichthyes, Serrasalminae), em relação ao tamanho corpóreo no reservatório Cajuru, bacia do rio São Francisco, Brasil
ABSTRACT. Stomach contents of Holoshesthes heterodoll Eigenmann, 1915 (Teleostei, Cheirodontinae), collected in the depletion zone ofCajuru reservoir when it was at its maximum water levei in two stations with different vegetal densities, were studied in order to investigate the influence ofthe flooded vegetal biol11ass on the food quantity and quality ingested by fi sh. Eighteen individuais from each station were examined. The standard length was 1.53±O.05 cm and 1.52±O.05 cm, respective1y at the lower biomass (8.19 kg dly weightJha) and higher biomass (38.10 kg dly weightJha) sampling stations. The stomach repletion Index (SRl) was applied for the quantitative ana1ysis. The alimentmy index (IA i) was used for the quali-quantitative analysis, with the volume of the items obtained through the points method. SR! did not show values significatively difterent between the two stations, p::::O.05 , by applying the Mann-Whitney test. ln both situations, Cladocera was the most important item. There were no correlation between the flooded vegetal biol11ass in lhe depletion zone and lhe intake of food by H. helerodon. However, as there were no empty stomachs, possibly even the lower vegetal biol11ass was enough to provide abundant feeding resources. KEY WORDS. Fish feeding, reservo ir, depletion zone, water leveI, vegetal biomass, Holoshesthes helerodol1.Reservoirs of tropical regions are young lakes and dominate fresh-water bodies in several are as (FERNANDO 1994). ln Brazil, and particularly in Minas Gerais State, the high number of dams, built for electric energy generation retains a significative portion of the superficial water volume (ELETROBRÁS 1990).The construction of hydroelectric dams and the consequent formation of artificiallakes arouses great changes in the fish community structure. The migratory species, also called piracema species, cannot transpose the barrier to complete their reproductive cycle, becoming less abundant upstream and downstream from the barrier and, in several times, absent in reservoirs (AGOSTfNHO et aI. 1992). ln these, the ichthyofauna becomes dominated by non-migrating species, of smaller size and low longevity (AGOSTINHO et aI. 1992). The changes tend to grow worse in rivers with successive dams (GODfNHO 1993).
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