Blood Gases, Hematocrit, Plasma Ion Concentrations, and Acid-Base Status of Musk Turtles (Sternotherus odoratus) during Simulated Hibernation

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Abstract
Musk turtles (Sternotherus odoratus) from Alabama were placed in simulated hibernation by submerging them at 3 C in normoxic and anoxic water. Animals were removed periodically from each condition without being allowed to breathe, and cardiac blood samples were taken for the determination of blood gases and acid-base parameters. Separate groups of turtles (n = 10 per group) were similarly maintained to determine their submergence viability. Anoxic turtles died in 21-31 days, while nine of 10 of those in normoxia were still alive after 150 days. Five of these survivors were removed and warmed at 22 C; three died, and two recovered completely. The acid-base status of turtles in anoxia deteriorated rapidly, while that of normoxic animals was essentially unaffected. Plasma [lactate] rose from 0.8 to 86 mM and [ ] fell from 25.3 to 2.6 meq/L during 25 days in anoxia, resulting in a drop in pH from 7.90 to 7.14; the corresponding 25-day values for turtles in normoxic water were 6 mM, 14.9 meq/L, and 7.99. After 150 days of normoxic submergence, pH (7.87) and [ ] (14.7 meq/L) remained essentially unchanged, while [lactate] rose slightly to 13.9 mM. Changes in inorganic ion concentrations, expressed as a percentage change from predive levels for 25 days of anoxic submergence and for 150 days of submergence in normoxic water, were, respectively: [Na⁺],-28% and-29%; [K⁺], +271% and +70%; [CI⁻],-50% and -38%; total [Ca], +1,084% and +97%; total [Mg], +324% and +26%. Similar values for hematocrit were-20% and +63%. Anoxic hibernation (as deep in mud) in excess of a week is considered unlikely for southern musk turtles, which do not tolerate anoxia as well as southern Chrysemys picta. A similar conclusion is avoided for northern musk turtle populations until the extent of any physiological cline in anoxia tolerance is investigated. It is argued that, for a given latitude, turtles most capable of aquatic gas exchange in normoxic waters are least capable of tolerating hypoxic/anoxic submergence.