Hibernation in freshwater turtles: softshell turtles (Apalone spinifera) are the most intolerant of anoxia among North American species.

Softshell turtles (Apalone spinifera) were submerged at 3 degrees C in anoxic or normoxic water. Periodically, blood PO(2), PCO(2), pH, plasma [Cl(-)], [Na(+)], [K(+)], total Ca, total Mg, lactate, glucose, and osmolality were measured; hematocrit and body mass determined; and blood [HCO(3)(-)] calculated. On day 14 of anoxic submergence, five of eight softshell turtles were dead, one died immediately after removal, and the remaining two showed no signs of life other than a heartbeat. After 11 days of submergence in anoxic water, blood pH fell from 7.923 to 7.281 and lactate increased to 62.1 mM. Plasma [HCO(3)(-)] was titrated from 34.57 mM to 4.53 mM. Plasma [Cl(-)] fell, but [K(+)] and total Ca and Mg increased. In normoxic submergence, turtles survived over 150 days and no lactate accumulated. A respiratory alkalosis developed (pH-8.195, PCO(2)-5.49 after 10 days) early and persisted throughout; no other variables changed in normoxic submergence. Softshell turtles are very capable of extrapulmonary extraction of O(2), but are an anoxia-intolerant species of turtle forcing them to utilize hibernacula that are unlikely to become hypoxic or anoxic (e.g., large lakes and rivers).