Efficiency, mechanics and motor control of fish respiration

Against the background of the unfavorable properties of water as a respiratory medium, the ventilatory system of fish appears efficient compared to that of mammals. Structural features upon which this high efficiency is based are discussed. Thus positional changes of the gill filaments during strong ventilation reduce the work of breathing. Further a strong coupling between the buccal and opercular pumps guarantees a uniform movement and constant hydrodynamic efficiency, regardless of the number of the driving forces, and their point of application. Thus changes in ventilatory demand can be met by adjustment of the number of active muscles. Prom the viewpoint of energy consumption this is advantageous, because muscle contraction efficiency is optimal at a specific load. Habitat correlated differences between fish species can be related to the timing of lower jaw abduction with respect to the volume changes of the pumps. Finally evidence is presented indicating the existence of a direct proprioceptive motor control.