<b>Feeding habit of <i>Oligosarcus robustus</i> Menezes, 1969 and<i>Oligosarcus jenynsii</i> (Günther, 1864) in the South of Rio Grande do Sul State</b>

Abstract

Oligosarcus robustus and O. jenynsii that inhabit the coastal lagoons of the extreme southern Brazil were characterized according to their morphologic variation and feeding structures as well as to their feeding habit. Specimens were collected in two periods (July and December 2001) in the Flores, Nicola, Jacaré and Mangueira lagoons. The food range was determined using the frequency of occurrence (FO%) and gravimetric methods (G%). A total of 164 specimens were analyzed, 67 of which had empty stomachs. The most frequent food items for O. robustus were insects FO=58,6%, fish FO=46,3% and crustaceans FO=12,2%. For O. jenynsii insects were dominant FO=83,9%, followed by crustaceans FO=35,7% and fish FO=26,8%. Insects were more frequent during summer for both species, Ephemeroptera and Odonata were the dominant groups. Fish were the main item in the diet of O. robustus during winter while O. jenynsii maintained the preference for the same group of insects during the cold season. The feeding strategy determined by the Amundsen graphic method showed that O. jenynsii is generalist preferring insects throughout the year while O. robustus is generalist opportunistic choosing insects during summer and fish in the wintertime.