Diadromous life cycle and behavioural plasticity in freshwater and estuarine Kuhliidae species (Teleostei) revealed by otolith microchemistry

Otolith microchemistry and microstructure were examined in juveniles of 3 Kuhlia species (Teleostei) from fresh and brackish environments in order to examine their migratory histories. All species presented with strontium: calcium (Sr:Ca) and barium: calcium (Ba:Ca) profiles in the inner region of the otoliths that suggested an obligatory marine larval phase. At approximately 0.3 to 0.6 mm from the otolith core, all individuals showed a sharp increase in Ba: Ca ratios that were generally associated with variation in the Sr: Ca ratio, indicating recruitment into rivers. Microchemical profiles in the outer region of the otoliths indicated a freshwater habitat for most K. rupestris and K. sauvagii and an estuarine habitat for most K. munda. Microstructure analyses validated the presence of an otolith check mark deposited during the habitat shift in K. rupestris and K. sauvagii, but not in K. munda. We hypothesise that this difference was due to lower osmotic stress for the fish moving from the sea to estuaries than from the sea to freshwater. This study demonstrated the ability of otolith multi-elemental microchemistry and microstructure to provide important insights on life history traits of species that lack basic biological information, such as those in the genus Kuhlia. The information provided in this study is critical for the conservation and management of these species.