Abstract
This analysis shows good intentions in the selection of valid and precise oxygen uptake ( 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 O 2 determinations, producing a histogram of the r 2 values and a plot of r 2 as a function of 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.