Oxygen consumption, blood lactate and inter-individual variation in the gulf killifish, Fundulus grandis, during hypoxia and recovery

Rates of oxygen consumption ((M) over dot(o2)) for Fundulus grandis, the gulf killifish, were measured in air-saturated water, at four progressively lower levels of oxygen and upon normoxic recovery. The pattern of (M) over dot(o2) versus oxygen partial pressure (PwO2) was that of an oxygen regulator, with a critical oxygen pressure (P-c) of 34 torr (1 torr = 133.3 Pa). Below this value, (M) over dot(o2) decreased and the concentration of blood lactate increased, indicating anaerobic metabolism during hypoxia. Recovery was characterized by elevated (M) over dot(o2) compared to the initial normoxic exposure, coupled with the rapid clearance of blood lactate. Variation in (M) over dot(o2) among the individual fish was appreciable and, in general, it was greater at higher levels of PwO2. This inter-individual variation was significantly larger than the variation between replicate measures of (M) over dot(o2) for a given individual, i.e. it cannot be attributed solely to random error. Furthermore, values for (M) over dot(o2) during normoxia were found to be repeatable when the same fish were used in multiple experimental trials. The observation of significant, repeatable inter-individual variation in (M) over dot(o2) suggests that such variation is a real and potentially important feature of fish metabolism. (C) 2000 Elsevier Science Inc. All rights reserved.