Aspectos bioecológicos del pejerrey Odontesthes bonariensis de la laguna de Monte

Abstract

In 1997
and 1998, two limnological processes of high relevance occurred in the Monte laguna: the invasion of Potamageton
pectinatlls and an extraordinary flood. The magnitude of theBe events affected the different components of the
ecosystem on a greater or smaller scale. The aims of this paper are to know the present status of the fish community
and the population ofpejerrey Odontesthes bonariensis, relating the results to the mentioned events. A limnologic
sampling considering physical and chemical parameters of water, quantification of macrozooplankton, and structure
of the fish community, was carried out. In the case of pejerrey, the cpue, the length-weight relationship, the K
factor, cephalic index, health status, age and growth, relative numerosity, reproductive and feeding aspects were
obtained. The physical-chemical composition of water is standard for this type of environment; the presence of
organochlorates conforms a symptom of alarm. The zooplankton was abundant and object of a strong predation
pressure by the fish. The present structure of the ichtyocenosis includes the carp, Cyprinus carpio. The captures
of pejerrey presented a marked decrease of the intermediate lengths, corresponding to 3+ and 4 + age, which
would be the annual classes most affected by the mentioned events. The causes of this could be an increase of
mortality because of greater predation pressure of larvae and juvenile)lsh and passive or active migration. Thus,
the present population is conformed by specimens 0[0+, 1 + and 2+ age, and those of a gt'eater size which survived
the flood and the presence of P pectinatus.