The Development of Form and Function in Fishes and the Question of Larval Adaptation

The Development of the Swim Bladder: Structure and Performance

Bernd Pelster

doi: https://doi.org/10.47886/9781888569582.ch3

Abstract.—The swim bladder originates as an unpaired dorsal outgrowth of the posterior foregut. While in physostome fish the embryonic connection to the pharynx persists, in physoclist fishes, it is lost during early development. In most fish larvae, the swim bladder is inflated shortly after hatching, just prior to the time of first feeding. At this time, many larvae swim up and start surfacing. In this case, initial inflation of the swim bladder is achieved by gulping air, and a lack of swim bladder inflation often is accompanied by a significant reduction of viability. While this appears to be the way most physostome fish inflate their swim bladder, some species obviously are able to inflate the swim bladder without surfacing. In adult fish, gas secretion into the swim bladder requires the activity of gas gland cells, which acidify the blood and thus induce a decrease in its gascarrying capacity. In consequence, gas partial pressures increase, providing a pressure head for the diffusive transport of gas from the blood into the swim bladder. Recent studies on the European glass eel Anguilla anguilla suggest that, at the time of first inflation, gas gland cells may not yet be functional. Nevertheless, glass eels can inflate their swim bladder without surfacing. Although various mechanisms have been proposed to explain the inflation of the swim bladder without gulping air, a decisive answer cannot yet be presented.