Valid oxygen uptake measurements: using high r (2) values with good intentions can bias upward the determination of standard metabolic rate

This analysis shows good intentions in the selection of valid and precise oxygen uptake ([Formula: see text] O(2)) measurements by retaining only slopes of declining dissolved oxygen level in a respirometer that have very high values of the coefficient of determination, r (2), are not always successful at excluding nonlinear slopes. Much worse, by potentially removing linear slopes that have low r (2) only because of a low signal‐to‐noise ratio, this procedure can overestimate the calculation of standard metabolic rate (SMR) of the fish. To remedy this possibility, a few simple diagnostic tools are demonstrated to assess the appropriateness of a given minimum acceptable r (2), such as calculating the proportion of rejected [Formula: see text] O(2) determinations, producing a histogram of the r (2) values and a plot of r (2) as a function of [Formula: see text] O(2). The authors offer solutions for cases when many linear slopes have low r (2). The least satisfactory but easiest to implement is lowering the minimum acceptable r (2). More satisfactory solutions involve processing (smoothing) the raw signal of dissolved oxygen as a function of time to improve the signal‐to‐noise ratio and the r (2)s.