Fish community structure of “Lago del Fuerte” reservoir, Tandil, Argentina

Abstract

Lago del Fuerte reservoir is a leisure center where sport fishing of silverside (Odontesthes bonariensis), a species stocked for this purpose, is very important. The objective of this paper is to determine the current fish community structure in this reservoir, their distribution, main trophic relationships and demographic parameters of the silverside population. The demersed vegetation present in the littoral region shapes favourable microenvironments for the development of shorter fish species; the silverside population use the pelagic region. The interspecific competition is reduced by means of habitat and/or trophic niche segregation. Astyanax eigenmanniorum is principally herbivorous; O. bonariensis is principally zooplanktophagous, and Cichlasoma facetum has a generalistic diet. There are very strong relationships between the different energetic levels present in the system. The zooplankton availability affects the silverside population parameters which affects its structure by means of predation; on account of the absence of piscivorous animals, fishermen act as predators affecting the populational dynamic parameters of silverside.