Evaluation of Opercular Catheterization as a Method for Sampling Water Expired by Fish

Abstract

Experiments were carried out on rainbow trout to see if cannulae implanted at different positions on the operculum yield accurate estimates of mean expired oxygen tension. This value is frequently used to calculate utilization or ventilation volume in fish and should therefore be accurately determined.Opercular oxygen tension [Formula: see text] recorded from seven quiescent fish (383–426 g, 10–12 C) in aquaria was highly variable with respect to time and cannula placement. Expired [Formula: see text] recorded from cannulae placed in the middle, upper, or lower part of the posterior margin of the operculum ranged from 54 to 157 mm Hg and was sometimes identical with inspired [Formula: see text]. When the fish were chased, expired oxygen tension usually rose but the magnitude of the rise and its duration were not uniform from cannula placement to placement. Other studies, on 21 trout (217–388 g, 10–12.5 C) whose gills were perfused with water at different flow rates with a mouth tube, indicated that the [Formula: see text] variability existed over a wide range of perfusion rates. In addition, [Formula: see text] levels from all three placements at perfusion rates approximating those of normal ventilation were frequently below the mean expired oxygen tension calculated from oxygen uptake and gill water-flow rate data.It is concluded that opercular cannulae provide poor estimates of mean expired oxygen tension in trout. The use of this technique to determine mean [Formula: see text] could lead to serious errors. It appears that large changes in oxygen utilization can be detected with opercular cannulae but any utilization values determined in this way would likely be erroneous.