ABSTRACT. – Strontium isotopic variations (⁸⁷Sr:⁸⁶Sr) were investigated in otoliths of an amphidromous goby, Sicydium punctatum, coming from a tropical insular river and showing contrasted depositional patterns of barium:calcium in otolith (Ba:Ca_otolith). In our study, varying as well as non-varying Ba:Ca_otolith individuals exhibited unchanged ⁸⁷Sr:⁸⁶Sr_otolith throughout the adult phase with values typical of stream water flowing through volcanic substrate (0.7053 ± 0.0003). These results unambiguously discard the Ba:Ca_otolith peaks as markers of migrations between freshwater and brackish estuarine water during the adult phase of the species and open on investigations of sources of variations on microhabitats or unknown physiological effects.