Alimentação de Oligosarcus longirostris Menezes & Gèry (Osteichthyes, acestrorhynchinae) do Reservatório de Salto Segredo, Paraná, Brasil Feeding of Oligosarcus longirostris Menezes & Gèry (Osteichthyes, acestrorhynchinae) of the Salto Segredo Reservoir, Paraná, Brazil

<abstract language="eng">In the feeding study of O. longirostris Menezes & Gèry, 1983, 211 stomachs from fish caught between March 1993 and February 1994 were analysed. Diet composition was analysed by the index of relative importance which deals with the numerical and gravimetric occurrence frequency. Results indicated that the species is piscivorous and its preferential food consisted oíAslyanax sp. 2. It was also found that Astyanax sp. 3 became an important food item, depending on the site of capture and its availability. Availability of prey seems to have a strong influence on the diet of O. longirostris. This same tendency has been observed during the different seasons of the year. Ontogenetic changes have also been found in the basic diet

Occurrence of Macrobrachium amazonicum (Heller) (Decapoda, Palaemonidae) in Leopoldo\u27s inlet (Ressaco do Leopoldo), upper Paran\ue1 River, Porto Rico, Paran\ue1, Brazil

Studies on the occurrence, temporal distribution and nychthemeral variation of Macrobrachium amazonicum (Heller, 1862) were undertaken in Leopoldo's Inlet, upper Paraná River, Porto Rico, Paraná, Brazil. Seventeen thousand and sixty specimens (11,786 larvae and 5,274 juveniles) were captured with a conicalcylindrical plankton net of mesh 0.5mm in monthly samples between February 1991 and February 1992. Results show that the greatest densities of larvae (301.83 larvae/10m³) and juveniles (168.8/10m³) of this species were caught in December 1991. Largest captures were made during the night. With regard to abiotic factors water temperature ranged from 20º to 30ºC, pH ranged from 5.66 to 7.37 and electric conductivity ranged from 51.83 to 65.33µS/cm. Relationship between the density of larvae and juveniles and abiotic factors was calculated by the Principal Components Analysis (PCA) which revealed the influence of some limnological variables especially on the distribution of larvae