OXYGEN-CONSUMPTION BY LARVAL JAPANESE MEDAKA WITH INFLATED OR UNINFLATED SWIM BLADDERS

Inflation and regulation of swim bladder volume enables fish to mainta in position within the water column with minimal energy cost. Larvae w hose swim bladders fail to inflate must move to stay suspended and wou ld be expected to use additional energy to maintain position. As a rel ative measure of extra effort expended by fish with uninflated swim bl adders, oxygen consumption rates at 26 degrees C were compared for lar val Japanese medaka Oryzias latipes with inflated and uninflated swim bladders. During the first 24 h after hatching, oxygen consumption rat es were significantly higher for larvae with uninflated swim bladders (1.75 +/- 0.13 mu g O-2 . h(-1). larva(-1)) than for those with inflat ed swim bladders (0.92 +/- 0.05 mu g O-2 . h(-1). larva(-1)); after 96 h, oxygen consumption rates had decreased for all larvae to about 0.6 mu g O-2 . h(-1). larva(-1). For larvae held in sealed con tainers fo r 72 h without access to free surface air, the volume of air-saturated water required to maintain an adequate concentration of dissolved oxy gen (>6 mg/L) was greater when swim bladders were uninflated (55 mL/la rva) than when swim bladders were inflated (36 mL/larva).