Survival mechanisms of the central mudminnow (Umbra limi), fathead minnow (Pimephales promelas) and brook stickleback (Culaea inconstans) for low oxygen in winter

Three species (central mudminnow, fathead minnow and brook stickleback) survive when a northern Wisconsin lake becomes anoxic in winter. Some gas bubbles beneath the ice contained as much as 11% oxygen when the lake water contained < 0.30 mg l super(-1) dissolved oxygen. Experiments conducted in the field determined that gas bubbles prolonged survival of all species, especially the mudiminnow and stickleback. In the laboratory, brook sticklebacks exhibited the lowest and fathead minnows the highest routine metabolic rate corrected for weight. Rate of gill ventilation of all three increased from 20 to 70 beats per minute as oxygen levels declined from 4.0 to 0.25 mg l super(-1). At low oxygen levels they moved to the upper one-third of the test tanks.