Combined use of otolith microchemistry and morphometry as indicators of the habitat of the silverside (Odontesthes bonariensis) in a freshwater-estuarine environment

Abstract

The silverside Odontesthes bonariensis is a highly salt-tolerant freshwater–estuarine species found in the Southern Hemisphere. The objective of the present study was to perform a simultaneous evaluation of the morphometry and microchemistry (Sr/Ca and Ba/Ca ratios) of the otoliths of this species to provide information on its displacements and to identify fish stocks. The morphometry and microchemistry of fish otoliths from three regions of the lower section of the Plata Basin (Uruguay River, Paraná River Delta and De la Plata River estuary) were compared. The results showed that otoliths of fish from the southern lower section of the Plata Basin tended to be circular in shape and had a lower ratio of sulcus perimeter to total otolith perimeter than those fish collected in the north of the studied region. There is a trend to increase the otolith Sr/Ca ratio with increasing water conductivity along a latitudinal (north–south) gradient, while the Ba/Ca ratio decreased significantly along such gradient. Present results suggest that the silverside population may be geographically divided along the north–south axis of the lower section of the Plata Basin.