Diet of two cichlid species, Cichlasoma facetum (Jenyns, 1842), and Gymnogeophagus rhabdotus Hensel, 1870, was studied in Rodó Lake, an urban hypertrophic lake in Uruguay. The stomach contents from 192 individuals of C. facetum and 202 of G. rhabdotus, obtained through seasonal sampling in the year 2000, were analyzed. The occurrence frequency and the alimentary importance index of each food item were calculated for each season and size class in both species. Cichlasoma facetum fed upon insects (mainly chironomid larvae and pupae), fish (Cnesterodon decemmaculatus Jenyns, 1842), and vegetals (algae, periphyton and macrophytes debris); large individuals also fed upon the freshwater shrimp Palaemonetes argentinus Nobili, 1901. Gymnogeophagus rhabdotus consumed zooplankton (mainly copepods), vegetals (algae and detritus) and Chironomidae larvae in a lesser extent.

ABSTRACT. Diet of Cnesterodon decemmaculatus (Jenyns, 1842) and Jenynsia multidentata (Jenyns, 1842) were analysed in Lake Rodó, an urban hypertrophic lake from Montevideo, Uruguay. Both species displayed omnivory. The most consumed items for C. decemmaculatus were zooplankton, periphyton, phytoplankton and detritus; the diet of J. multidentata included zooplankton, insects, crustaceans and juvenile fish. Our results suggest that both species could be acting as facultative planktivores. The fish community of this lake is characterised by the dominance of C. decemmaculatus and J. multidentata. Under this condition, predation on large-bodied zooplankton could indirectly be contributing to maintain a high phytoplankton abundance and a low water transparency.KEYWORDS. Fish feeding, facultative planktivores, eutrophication. RESUMEN. Dieta deCnesterodon decemmaculatus (Poeciliidae) y Jenynsia multidentata (Anablepidae) en un lago hipereutrófico de Uruguay. Se analizaron las dietas de Cnesterodon decemmaculatus (Jenyns, 1842) y Jenynsia multidentata (Jenyns, 1842) en el Lago Rodó, un lago urbano hipereutrófico de Montevideo, Uruguay. Ambas especies mostraron un comportamiento omnívoro. Los ítems más consumidos por C. decemmaculatus fueron zooplancton, perifiton, fitoplancton y detritos; la dieta de J. multidentata incluyó zooplancton, insectos, crustáceos y peces juveniles. Estos resultados sugieren que ambas especies pueden actuar como planctívoros facultativos. La comunidad de peces de este lago se caracteriza por la dominancia de C. decemmaculatus y J. multidentata. Bajo esta condición, la depredación sobre el zooplancton de gran tamaño podría indirectamente estar contribuyendo a una alta abundancia de fitoplancton y una baja transparencia del agua.PALABRAS CLAVE. Alimentación de peces, planctívoros facultativos, eutrofización.