Summary

The swimbladder volume and air volume within the breathing chambers of the anabantoid fish Colisa lalia have been measured. These data help in the understanding of some of the functions of these organs and are necessary for an analysis of their role in hearing and sound production. By means of a simple trick (based on new data) it was possible to analyse the time course of air volume changes in the breathing chambers at different temperatures. The results are well described by a simple diffusion model. The temperature-dependence of the time course suggests an interesting increase of the diffusion constant with temperature. Under constant conditions the chambers were always filled with about the same volume of air. No excess pressure was found. Typical values of a single chamber's air content range from 34 to 58/J. Air content increases with about the third power of fish length. By using the present data, the time course of air volume changes in the chambers of a given fish can be estimated. Swimbladder volumes, determined using Boyle's law, ranged from 70 to 220 /A and were also found to increase with about the third power of fish length, in accordance with a simple estimation. The data are discussed in relation to buoyancy, diffusion processes, blood circulation, hearing and sound production and suggest some interesting new work