In 1938, Van Dam obtained the first direct measurements of ventilation volume in restrained fish by using a rubber membrane, stretched around the fish’s head, to separate inspired and expired water. In the ensuing 50 years, modifications of this technique have been widely applied in studies of fish physiology (e.g. Davis and Cameron, 1971). Current methods for measurement of in freely moving fish (Saunders, 1962; Holeton and Randall, 1967) are indirect and require accurate determination of inspired and expired oxygen tensions, and oxygen consumption . While can be easily determined, measurement of can be troublesome.
Studies by Davis and Watters (1970) have shown measurements from catheters inserted through the operculum to be position-sensitive and, therefore, extremely variable. Some authors (Kiceniuk and Jones, 1977) have tried to circumvent this problem in swimming fish by sewing a rubber ‘skirt’ between the mouth and opercula to...
