RESUMEN
A laboratory burrow and mudflat system was used to examine aspects of burrow air-phase maintenance and utilization by the amphibious mudskipper Scartelaos histophorus. While confined to its burrow during simulated 'high tide', this species respires both aquatically and aerially, in the latter case utilizing an air phase it had established by transporting air into the burrow during simulated 'low tide'. Over the course of 'high-tide' confinement, burrow-water P(O2) declines, making the air phase more important for respiration; the burrow-water O2 tension eliciting air-phase respiration is 4.8+/-0.2 kPa. At 'low tide', when the fish has access to air, it deposits new air in the air phase by transporting gulps into the burrow and releasing them. Observed air-deposition rates for both males and females were 12.3+/-4.5 trips h(-1). All of the fish tested (N=8 individuals + 2 pairs) deposited air and responded to experimental air-phase withdrawal by replacing the air (72 of 74 tests, 97.3%). Also, repeated tests with one fish showed that experimental reduction of the air-phase P(O2) by mixing with N2 elicited a gas-expelling behavior at O2 levels less than 10.3 kPa. At O2 levels greater than 10.3 kPa, the fish left the air phase intact and added to it by depositing surface air.