The role of lactic acid in gas secretion in the teleost swimbladder

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1. 1. Existing evidence for the mechanism of gas secretion into the swimbladder of fish suggests that lactic acid is produced by the gas gland tissue in the presence of high oxygen pressure and is responsible for the “single concentrating effect” (Kuhn & Kuhn, 1961) which is multiplied by countercurrent blood flow through the rate mirabile to produce the necessary gas pressure. 2. 2. The catabolism of the gas gland tissue of the vermilion rockfish, Sebastodes miniatus, a species whose ecological depth range extends down to 200 m, has been investigated under O 2 pressures up to 51 atm. Lactic acid was produced by the tissue throughout the range of pressures investigated, and no evidence of a Pasteur effect was found. CO 2 production by the tissue was similar and very low under both O 2 and N 2 and suggested that citric acid cycle enzymes and oxidative phosphorylation systems were very weak in this tissue. 3. 3. The maximum glycolytic rates observed were too low to account for pre- and post-rate differences in lactate concentration observed by other workers, and glycogen levels in the gas gland tissue (0·02 mg/mg dry wt.) could produce the observed arteriovenous differences in lactate for only a few minutes. 4. 4. The essential role of lactic acid in gas secretion was supported by injecting oxamic acid, a competitive inhibitor of lactic dehydrogenase, into the swimbladder of deflated fish; statistically significant differences in control and experimental groups in both amounts and relative percentages of gases secreted were observed.