Mudskipper Periophthalmodon schlosseri can repay oxygen debts in air but not in water

We determined aerial and aquatic oxygen uptake rates (Mo-2) of Periophthalm odon. schlosseri at rest and after exhaustive exercise at 30 degrees C. Res ting Mo-2 in air (3.16 +/- 0.10 [SE] mu mol/g/hr) was significantly higher than that in air saturated water (2.41 +/- 0.06 mu mol/g/hr). When the fish was placed in air after 2 min exhaustive exercise, Mo-2 immediately increa sed about 2.5 times, thereby repaying oxygen debt of 5.0 mu mol/g. In contr ast, Mo-2 failed to show any significant elevation from the resting level a s long as the fish was confined in water after exercise. However, when the fish was subsequently emerged, Mo-2 did increase above the resting level, a mounting to an excess oxygen uptake of 5.5 mu mol/g. These results demonstr ated that the gas transport system of P. schlosseri is better adapted to ai r breathing and the mode of adaptation limited the capability for water bre athing. (C) 1999 Wiley-Liss, Inc.