Arterial blood gas levels and cardiovascular function during varying environmental conditions in a mudskipper, Periophthalmodon schlosseri

Changes in blood gas levels, blood pressure and heart rate were studied in chronically cannulated mudskippers, Periophthalmodon schlosseri, subjected to air exposure (6 h), aquatic hypoxia with access to air (water PO₂ <0.9 kPa, 6 h) and forced submersion in normoxic water (12 h) at 30°C. Air exposure did not affect either blood O₂ and had little effect on blood CO₂ levels, but blood pH increased slightly, but significantly. Blood ammonia concentration was elevated sixfold during air exposure. Aquatic hypoxia caused no significant changes in blood gas levels. When the fish was forcibly submerged, blood O₂ saturation decreased rapidly to approximately 30%. Blood PCO₂ and total CO₂ also decreased, but blood pH was unaffected by forcible submersion. Air exposure did not affect blood pressure or heart rate. Aquatic hypoxia did not affect blood pressure but transiently increased heart rate. In contrast, forced submersion significantly depressed heart rate throughout the period of submersion, while blood pressure decreased only transiently. Upon emersion, the heart rate immediately increased to above the control level when the fish took its first air breath.