The oxygen consumption is an indirect measure of the breathing rate of an organism, and is an important factor to incorporate into ecological models of economically and scientifically important bays. The models require reliable data on how this breathing rates change according on the physiological state the most common organisms are in, as well as the way rates change with the seasons. As Cancer setosus is one of the most common invertebrates found in Paracas bay, in-situ experiments, using a system of underwater chambers, were carried out to measure how oxygen consumption rates vary with age, sex and reproductive state on summer (March) and winter (September). Results (μmolO2 min-1 g-1) show that: (1) Breathing rates (y) decreases as the size (x) increases on males and females, a tendency that remained in both seasons (Males: summer y = -0.0182x + 0.2626, winter y = -0.0097x + 0.1713; females summer: y = -0.0212x + 0.2732, winter y = -0.0095x + 0.1744). (2) No significant differences in the breathing rates were found between sexes in juveniles and adults on neither of the seasons sampled. And (3) in brooding females a clear increase in the breathing rate was measured as the developmental stage of the eggs progressed on winter (early stage: 0.037 vs. late stage: 0.073) but was not the case on summer where no significant differences were found (early stage: 0.055 vs. Late stage: 0.063). Possible reasons of this behaviour are, here by, discussed by the authors.