Effects of Oxygen Depletion and of Carbon Dioxide Buildup on the Photic Behavior of the Walleye (Stizostedion vitreum vitreum)

Abstract

In laboratory experiments under overhead white light, walleyes (Stizostedion vitreum vitreum (Mitchill)) displayed a negative phototactic response consistent with field observations and histological features of the walleye eye. The strength of this innate response proved to be largely dependent on the given respiratory situation: during oxygen depletion and during buildup of free carbon dioxide, this response diminished to the point of obliteration, which occurred at levels leaving mobility and equilibrium of the test specimens still intact. Whereas during the course of oxygen depletion a wide indifference zone (little or no change of light behavior) could be observed from saturation (= acclimation) level down to about 4–2 mg/liter, the fish reacted rather sensitively to increase of free carbon dioxide. Starting from acclimation levels of 1.0–2.0 mm Hg CO₂, the light avoidance response declined gradually while approaching tensions of 5 mm Hg or more, being completely abandoned at levels above 15 mm Hg. This effect could not be attributed to pH shifts.