Ontogenetic changes in the food items assimilated by Plagioscion squamosissimus (Perciformes: Sciaenidae) and Hypophthalmus edentatus (Siluriformes: Pimelodidae)

Abstract

In order to identify the ontogenetic changes in the food items assimilated by the larvae of Plagioscion squamosissimus and Hypophthalmus edentatus, we analyzed the stomach content and the nitrogen isotopic value (δ 15N) from the larvae. Samplings were performed monthly, from October 2002 to March 2003, and October 2003 to March 2004 in the subbasin of the Ivinheima River (Upper Paraná River floodplain), Mato Grosso do Sul State, Brazil. The food items assimilated by the larvae of P. squamosissimus changed with respect to the developmental stages. In the preflexion stage, we found a large contribution of phytoplankton, followed by zooplankton. During the flexion and post-flexion stages, we recorded a decrease in phytoplankton contribution, an increase in zooplankton contribution, and the presence of zoobenthos. In H. edentatus, phytoplankton made the greatest contribution, followed by zooplankton. Ontogenetic changes in δ 15N for this species were not detected. For both species, the food item predominantly ingested was not the assimilated one, except for the last two developmental stages of P. squamosissimus.