APPLICATION OF OTOLITH ANALYSIS FOR ELUCIDATION OF LIFE-HISTORY AND DEMOGRAPHIC PARAMETERS IN PEJERREY

OKAJIMA, H.; MIRANDA, L. A.; YAMAMOTO, Y.; COLAUTTI, D. C.; YOKOCHI, H.; STRUSSMANN, C. A.; BERASAIN, G. E.

CABA

Jornada; XX Jornadas Anuales de la Sociedad Argentina de Biología y XVII Jornadas de la Sociedad Uruguaya de Biociencias.; 2018

Sociedad Argentina de Biología

The pejerrey Odontesthes bonariensis is one of the most important inland water fisheries resources in the Pampa region. Pejerrey populations inhabit an extensive network of rivers and shallow lakes where environmental conditions may vary from hyposaline to hypersaline and with temperature fluctuations sometimes in excess of 25ºC. This area is also characterized by decadal cycles of droughts and inundations that impart marked changes in the water bodies? levels, connectivity, physico-chemical parameters, nutrients, primary production and trophic structure. In this environment, natural pejerrey populations show marked fluctuations in abundance, from hyper abundance and dominance over other species to mass mortality and even complete disappearance in some years, but the causes are still not clear. Analyzes of otolith microstructure and chemistry can provide information useful for the estimation of age, birth date, past growth rates, migration, and even the past environment experience of individual fish, and hence for the study and management of natural pejerrey resources. In this study, we used Electron Probe Micro Analysis (EPMA) to examine the chemical composition of the otoliths of juvenile and young-of-the-year pejerrey specimens collected in Chascomús lake in 2016 in relation to environmental variables. We applied a novel method to equate the EPMA results, which are usually referred in terms of distance from the otolith nucleus, to calendar dates, and which facilitates the examination of causal relationships between otolith chemistry and environmental factors in wild populations. The EPMA results, combined to birth date estimation based on otolith increment counting, revealed that both salinity and temperature affect otolith Sr content. Fish with different birth dates or sizes generally had similar otolith Sr composition, but some minor differences noted could reflect size- or cohort-dependent habitat segregation. The results also allowed clear discrimination of native, resident individuals and immigrants. Otolith analyzes may provide crucial insight on the biology of natural pejerrey populations.