Ecología trófica del pejerrey (<i>Odontotesthes bonariensis</i>) en la laguna del Venado y Alsina, dos ambientes del sistema Encadenadas del Oeste, prov. de Buenos Aires

Abstract

The aim of the present study was to analyze the feeding of the silverside Odontesthes bonariensis in the Venado and Alsina lake. which are part of the Encadenadas del Oeste lake system. The stomach content of 206 individuals was analyzed. Total length ranged from 93 to 585 mm. The vacuity index (VI) and repletion index (RI) were estimated by season and site. Index of Relative Importance (IRI) for each food category and the trophic level (TL) of pejerrey were calculated by site. The diet of the silverside was composed of 68 prey items, most of which were occasional preys. Copepods and cladocerans were the main prey items in the diet in both lagoons. Copepods were the most important item in Venado lagoon and cladocerans were so in Alsina lagoon. The micro crustaceans were the main prey item for both size classes, however their %IRI decreased in the larger fish (95% IRI for the 93-299 mm Tl size class and 63% IRI for the 300-585 mm Tl size class). Silverside TL estimated for each lagoon (TL= 3) characterizes it as secondary consumer.