F. Scasso  & H. Campos
 

ABSTRACT

Two populations of silverside Odontesthes bonariensis, a species introduced  in Laguna Grande of San Pedro (Laguna Grande) and Laguna Chica of San Pedro (Laguna Chica) were studied. These lakes belong to the Biobío river basin (Central Chile) and present processes of eutrophication, being identified as eutrophic and mesotrophic lakes respectively. The parameters analyzed were: biomass, production, length frequency, weight-length relationship, condition factor, age and growth. O. bonariensis, the most abundant species in the two lakes, presented high values of biomass, production and yield, showing its adaptation to lakes of medium and high eutrophic status. Laguna Chica sustained bigger amounts of biomass and production of silverside than Laguna Grande, confirming the hypothesis that in an intermediate phase of eutrophication there is a higher increment in the abundance of the populations of certain species, in comparison to an ecosystem with high enrichment levels. Besides, the population of Laguna Chica reached an asymptotic length and a longevity that exceeded the values corresponding to Laguna Grande. However, individuals of Laguna Grande were stoutter, since the advanced state of eutrophication of this lake would be conditioning a higher availability of food, reflecting a better condition of the fish.