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

We determined aerial and aquatic oxygen uptake rates (&Mdot;o(2)) of Periophthalmodon schlosseri at rest and after exhaustive exercise at 30 degrees C. Resting &Mdot;o(2) in air (3.16 +/- 0.10 [SE] &mgr;mol/g/hr) was significantly higher than that in air saturated water (2.41 +/- 0.06 &mgr;mol/g/hr). When the fish was placed in air after 2 min exhaustive exercise, &Mdot;o(2) immediately increased about 2.5 times, thereby repaying oxygen debt of 5.0 &mgr;mol/g. In contrast, &Mdot;o(2) failed to show any significant elevation from the resting level as long as the fish was confined in water after exercise. However, when the fish was subsequently emerged, &Mdot;o(2) did increase above the resting level, amounting to an excess oxygen uptake of 5.5 &mgr;mol/g. These results demonstrated that the gas transport system of P. schlosseri is better adapted to air breathing and the mode of adaptation limited the capability for water breathing. J. Exp. Zool. 284:265-270, 1999. Copyright 1999 Wiley-Liss, Inc.