THE COMPOSITION AND FUNCTION OF SURFACE-ACTIVE LIPIDS IN THE GOLDFISH SWIM BLADDER

Goldfish (Carassius auratus: Cyprinidae) have a two-chambered su,im bladder The anterior chamber is thick walled undergoes small volume changes does not empty itself of gas, and assists in hearing The posterior chamber is thin walled: undergoes extensive volume change that often results in bladder collapse, and controls animal buoyancy. Both chambers possess relatively thick inner lipid linings that differ in composition. The anterior-chamber lipids are rich in cholesterol and phospholipids, particularly in disaturated phospholipids. Posterior-chamber lipids are exceptionally rich in cholesterol but not in saturated phospholipid. Lipids from both chambers lower surface tension below that of water but are not more surface active than a cell membrane preparation. This study demonstrates a new technique for determining the role of the lipids in bladder inflation and compliance. The pressure required to initiate the inflation of a collapsed bladder (termed ''opening pressure'') increased after lipids were removed from the posterior chamber but nor after they were removed from the anterior chamber Posterior-chamber lipids act as an antiglue for collapsed bladders by preventing the folded inner surfaces from adhering Anterior-chamber lipids did not net as an antiglue, and their function remains unknown.