ABSTRACT
Dissolved oxygen is an unpredictable resource for fishes in tropical freshwater ecosystems. Environmental temperature interfaces with air-breathing physiology of aquatic ectotherms because it influences the rates of metabolic processes as well as environmental oxygen availability and diffusivity. Significant variance among the various treatments was detected with repeated measures multiple analysis of variance. Animals in the dietary experiment were statistically uniform for all measured variables except venous oxygen tension. Air-breathing behavior and physiology were remarkably consistent between groups of Hypostomus regani differing in their dietary status; fed and unfed fish had virtually identical responses to hypoxia. Although dietary treatment did not affect mean air-breathing behavior and physiology, coincident monitoring of air-breathing activity and heart rate revealed substantial inter-individual variation in both behavior and physiology, and a connection between the two. In animals chronically acclimated to 20°, 25° and 30°C, gill ventilation was temperature insensitive.
