OXYGEN CONSUMPTION OF EUPHAUSIA PACIFICA: THE LACK OF A DIEL RHYTHM OR LIGHT‐DARK EFFECT, WITH A COMPARISON OF EXPERIMENTAL TECHNIQUES1

Abstract

We found no evidence for diel rhythms in the respiration of individual Euphausia pacifica during long‐term (11–32 hr) Warburg manometric experiments. Changes from light (1.2 × 102 µw cm−2) to dark (<1.8 × 10−5 µw cm−2) also had no appreciable effect on oxygen consumption of most of these euphausiids. Respiratory rates often decreased with time regardless of light conditions, but 2 of 20 animals respired consistently more in the dark than the light.Larger animals consumed less oxygen per unit weight than smaller ones. This factor contributed to differences between mean oxygen consumption rates of separate experiments. Although we obtained higher rates from the Winkler than the manometric method, the differences were not significant. The average rate (1.34 µl O2 mg−1 hr−1) from all our experiments (79 animals) was intermediate in the range of values reported in the literature.