Oligosarcus

Abstract: A new characid species is described from the rio Jacui basin, a coastal drainage from southern Brazil. Itis morphologically most similar to its sympatric congeners Oligosarcus jenynsii and O. jacuiensis , but can be distinguished from both species in having the interorbital region wider and the pectoral fin shorter and additionally from O. jenynsii in having a smaller orbital diameter.

Abstract: The analysis of the distribution patterns presented by examples of freshwater fishes restricted to headwater habitat: the anostomid Leporinus octomaculatus, the characins Jubiaba acanthogaster, Oligosarcus perdido, Moenkhausia cosmops, Knodus chapadae, Planaltina sp., the loricariid Hypostomus cochliodon, and the auchenipterid Centromochlus sp. provided evidences of a relatively recent shared history between the highlands of the upper rio Paraguay and adjoining upland drainage basins. Restricted to headwater of the uplands in the upper rio Paraguay and adjoining basins, these species provide biological evidence of the former extension of the central Brazilian plateau before the origin of the Pantanal Wetland. Disjunction took place due to an ecological barrier to these rheophilic taxa represented tectonic subsidence related to the origin of the Pantanal Wetland. Molecular analysis of Jubiaba acanthogaster revealed that the sample from the upper rio Xingu basin are the sister-group of a clade that includes samples from the upper rio Arinos (upper rio Tapajos) plus the upper rio Paraguay basin, supporting the assumption that the origin of the upper rio Paraguay basin causing vicariance between this basin and the upper rio Tapajos is the least vicariant event in the evolutionary history of the group. A analise do padrao de distribuicao apresentado por exemplos de peixes de agua doce neotropicais restritos a habitats reofilicos de cabeceira: o anostomideo Leporinus octomaculatus, os caracideos Jubiaba acanthogaster, Oligosarcus perdido, Moenkhausia cosmops, Knodus chapadae, Planaltina sp., o loricariideo Hypostomus cochliodon e o auquenipterideo Centromochlus sp. fornecem evidencias de uma historia compartilhada relativamente recente entre as terras altas do alto rio Paraguai e bacias de terras altas vizinhas. Restritas as cabeceiras das areas altas nas bacias do alto rio Paraguai e bacias vizinhas, estas especies fornecem evidencias biologicas da preterita extensao do Planalto Central Brasileiro anteriormente a origem tectonica da planicie alagavel do Pantanal. Disjuncoes ocorreram devido a barreira ecologica para estes taxons reofilicos representada pela subsidencia tectonica associada a origem do Pantanal. A analise molecular de Jupiaba acanthogaster revelou que amostras da bacia do alto rio Xingu consistem no grupo-irmao de um clado mais inclusivo que inclui amostras do alto rio Arinos (alto rio Tapajos) mais o alto rio Paraguai, suportando a suposicao de que a origem do alto rio Paraguai causou vicariância entre esta bacia e o alto rio Tapajos no ultimo evento vicariante na historia evolutiva do grupo.

Abstract: Novakowski, G.C., Hahn, N.S. & Fugi, R. Feeding of piscivorous fish before and after the filling of the Salto Caxias Reservoir, Parana State, Brazil. Biota Neotrop. May/Aug 2007 vol. 7, no. 2. http://www. biotaneotropica.org.br/v7n2/pt/abstract?article+bn04107022007. ISSN 1676-0603. This study investigated the feeding patterns of piscivorous fish before and after the filling of Salto Caxias Reservoir, Parana State, Brazil. Specifically, it was determined if the diet of Hoplias malabaricus, Oligosarcus longirostris, Rhamdia branneri and Rhamdia voulezi altered according to prey availability. Fish were sampled monthly from March 1997 to February 1998 (pre-impoundment period) and from March 2000 to February 2001 (post-impoundment period) within the reservoir. Stomach contents of 549 individuals were analyzed and the diet was described as occurrence and volumetric percentage of each item combined in a feeding index. The piscivorous habit was, overall, more evident in H. malabaricus, O. longirostris and R. voulezi. However, for R. branneri mollusks and crabs were more important than fish. After the impoundment, most consumed prey was Astyanax sp. b and Cyphocharax modestus for three of the predators. These prey species were more abundant after the impoundment. Then, there are evidences that the availability, abundance and vulnerability of prey in the reservoir environment are the most important factors influencing predator’s choice.

Abstract: Oligosarcus jenynsii and Oligosarcus robustus are fishes of Characidae family that occur in Rio Grande do Sul, Uruguay and northern Argentina. This work purported to study the feeding dynamics (repletion and hepatosomatic indexes and condition factor) over time, and to investigate the coexistence of these two species by evaluating the partition of resources using qualitative and quantitative analyses of diet, temporal and spatial segregation throughout the water column and some ecomorphological aspects of the species in the Lagoa Fortaleza. Specimens were sampled monthly, from May 2000 to April 2001 during 24 h/month, using stationary gill nets of different mesh sizes. The records of each individual included total and standard length; total, stomach and liver weight; sex and stomach repletion. The variation of the mean values of repletion index and relative frequencies of stomach repletion stages indicate that O. jenynsii and O. robustus do not present seasonal differences in feeding intensity. The hepatosomatic index shows an allocation of energy to the liver during every period except reproduction, when part of the energy is used for gonad maturation. The estimated condition factor for both species reveals an increase in the reproductive period, evidencing the influence of gonads upon the condition of the fish. The diet analysis revealed that O. robustus is piscivorous, whereas O. jenynsii is a generalist carnivore, tending to piscivory as well. The active period of O. robustus is more concentrated at sunrise and sunset, whereas O. jenynsii is continually active, a characteristic related to hunting for prey. The ecomorphological analysis revealed differences between the two species in the dimensions of the mouth. Evidence suggests that the species coexist, sharing food sources, differing in oral morphology but ingesting similar prey, possibly because food is not a limiting factor in the environment.