Artículo de publicación ISIStandard and active metabolisms determine the key aspects of the development and survival of fish species. We describe the first bioenergetic model for the standard metabolic rate (SMR) and active metabolic rate (AMR) of the Chilean native darter Percilia irwini. Adult individuals (5.5 1.2 cm, 2.1 0.9 g) were tested in a Blaska-type respirometer at 19.5 0.5C. Fish held a position by resting at the bottom at low velocities (5 and 15 cm s 1 ) and by swimming at higher velocities (25 and 35 cm s 1 ). SMR ¼ 0.166 M1.39 with an average of 220 mg O2 h 1 kg 1 . Two bioenergetic models for AMR were adjusted. AMR ¼ 0.16 M1.16U0.23 at low velocities and AMR ¼ 0.026 M0.77U0.97 at higher velocities. Therefore, low velocities have little effect on the active metabolism of this species, but it is the main factor at higher velocities. Metabolic scope per unit weight was larger for smaller individuals, which is consistent with the faster growth of younger individuals.