HOLMAN, J.D.*; BURNETT, L.E.; BURNETT, K.G.; JORGENSEN, D.D.; Univ. of North Texas; College of Charleston; College of Charleston; Roanoke College: The Depression of Oxygen Uptake in Blue Crabs in Response to Bacterial Challenge

We investigated the respiratory responses of the blue crab, Callinectes sapidus, to an injection of bacterial pathogen Vibrio sp. 90-69B3. Current results suggest that bacteria are removed from the hemolymph in a process associated with a reduction in circulating hemocytes. It is thought that the gill is an important site of accumulation and ultimate removal of the bacteria. We tested the hypothesis that the accumulation of bacteria at the gills disrupts gas exchange. Whole animal oxygen uptake was measured in well-oxygenated water (25 ppt, 25&degC) in control animals injected with a saline and compared with animals injected with 2.5 x 10⁴ live Vibrio/g crab weight. Injections were made directly into the lumen of the heart to promote rapid distribution of Vibrio. Crabs injected with Vibrio had a significantly (p<0.037, t-test) depressed oxygen uptake (2.56 &#956mol/g-h, 0.23 sem, n=6) compared with controls (4.53 &#956mol/g-h, 0.59 sem, n=6) in a period of 1 to 2 hours after injection. In separate experiments we compared pre- and postbranchial hemolymph Po₂ and pH in sham-injected controls with the same variables in Vibrio-treated crabs 30 min after treatment. Postbranchial Po₂ was significantly (p=0.006, t-test) depressed in Vibrio-treated crabs (99 torr, 5.8 sem, n=9) compared with the controls (122 torr, 3.4 sem, n=7). There were no significant differences in any of the other variables. Hemolymph pressure was measured in the infrabranchial sinus and the pericardial space unilaterally before, during and after sham and Vibrio injection, allowing for calculation of hemolymph pressure drop across the gill circuit. Ventilatory function, monitored as pulsatile hydrostatic pressure in the branchial chamber, did not change significantly after either sham or bacteria injection. Resistance to hemolymph flow increased across the gill circuit after bacterial injection. These results suggest that injection of crabs with Vibrio results in a disruption of gas exchange at the gills, supporting our hypothesis. The precise mechanisms involved are not yet clear and are currently under investigation. (Supported by NSF IBN-0212921.)