Exercise and forced submergence in the pond slider (Trachemys scripta) andsoftshell turtle (Apalone ferox): Influence on bimodal gas exchange, diving behaviour and blood acid-base status

The dynamics of bimodal respiration, diving behaviour and blood acid-base s tatus in the softshell turtle Trachemys scripta and the pond slider Apalone ferox were investigated at rest and under conditions of stress induced by exercise and forced submergence. During periods of forced submergence, only A. ferox doubled its aquatic gas exchange rate. Both A, fel ox and T, scri pta increased their aerial gas exchange profoundly following exercise and f orced submergence, a pattern indicative of increased anaerobic respiration. Emersion duration increased significantly in A. ferox following forced sub mergence, and mean apnoeic time decreased significantly in A. ferox followi ng exercise, indicating that a larger proportion of time at the surface was spent ventilating. Also, A. ferox maintained a one-breath breathing bout r egardless of treatment. Submergence produced a respiratory acidosis in the plasma of approximately 0.2 pH units in magnitude in T, scripta and a mixed respiratory/metabolic acidosis of 0.4 pH units in A. ferox. Exercise induc ed an acidosis of 0.2 pH units of primarily metabolic origin in both specie s. Intra-erythrocyte pH was also reduced in both species in response to sub mergence and exercise, Both intracellular and extracellular acidoses were m ore severe and longer lasting in A, ferox after each treatment, Plasma [HCO 3-] decreased by 25 % in both species following exercise, but only in A. fe rox following submergence. Plasma lactate concentrations increased by equal amounts in each species following exercise; however, they returned to rest ing concentrations sooner in T, scripta than in A. ferox, A, ferox had sign ificantly higher lactate levels than T, scripta following forced submergenc e as well as a slower recovery time. A, ferox, which is normally a good bim odal gas exchanger at rest, utilizes aerial respiration to a greater extent when under respiratory and/or metabolic stress. T, scripta, although almos t entirely dependent on aerial respiration, is physiologically better able to deal with the respiratory and metabolic stresses associated with both fo rced submergence and exercise.