We evaluated the influence of water temperature (Tw) oil the energy acquisition and use in the chilean silverside Basilichthys australis (Eigenmann 1927), an endemic species inhabiting freshwater ecosystems in Chile. We tested the effect of Tw (11.5, 14.0, 18.0, 22.0 and 26.0 degrees C) on food intake, digestibility, food transit time and metabolic rate. As expected, this study demonstrated that many physiological variables under study were significantly affected by Tw, as well as the net energy balance of this species. Nevertheless. the net energy balance was not strictly related to the range of Tws evaluated. At Tws lower than 14 degrees C the energy budget was depressed, because food intake was lower than at Tws between 14 and 26 degrees C. where food intake was higher and independent of Tw. Consequently, at these temperatures the energy balance was positive and also independent of Tw. Physiologically, B. australis appears to be a tolerant species with respect to the wide range of water temperature in habitats at different depths. Thus. its distributions may extend through the entire profile of lakes and rivers, even in systems characterised by spatial and temporal thermal variability.