SHORT COMMUNICATION MEASUREMENT OF VENTILATION VOLUME IN SWIMMING TUNAS

In 1938, Van Dam obtained the first direct measurements of ventilation volume (VG) 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, modifi-cations of this technique have been widely applied in studies of fish physiology (e.g. Davis and Cameron, 1971). Current methods for measurement of VG in freely moving fish (Saunders, 1962; Holeton and Randall, 1967) are indirect and require accurate determination of inspired (Pich) ar>d expired ( P E O J oxygen tensions, and oxygen consumption (VQJ- While Pio2 can be easily determined, measurement of PEQ2 can be troublesome. Studies by Davis and Watters (1970) have shown PE O 2 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 ensure mixing of expired water and to separate it from the surrounding water. Even when expired water POl can be determined accurately