Meeting Abstract

P1-94   -   Static Instability and the Swim Bladder: Using Micro -CT Scans to Measure the Center of Mass and Center of Buoyancy in Bluegill Sunfish Fath, MA*; Donahue, J; Nguyen, S; Lee, R; McMenamin, S; Tytell, ED; Tufts University; Boston College; Boston College; Boston College; Tufts University michael.fath117@gmail.com

Many fishes have a swim bladder which changes in volume to maintain neutral buoyancy. Changes in swim bladder volume can subsequently change the distribution of volume and the distribution of mass throughout the fish. Changes in volume and mass distribution will lead to changes in the locations of the center of buoyancy (COB) and center of mass (COM), respectively. Since the buoyant force pulls upward at the COB and gravity pulls downward at the COM, changes in the location of these points could potentially lead to changes in static stability of the fish. If the COM were directly below the COB then these forces will act to orient the fish dorsal-side up, without any input from the fish. Any other configuration will result in destabilizing pitching or rolling torques that the fish must actively counter to maintain a dorsal-side up orientation. To determine if changes in swim bladder volume are correlated with increases in destabilizing torques in bluegill sunfish, we compared the relative locations of the COM and COB in control fish and fish with varying amounts of the air removed from the swim bladder. We used fish models generated from segmented micro-CT scans to calculate the location of the COM and COB. We found that the distance between these two points was small (<0.5 %BL) and did not correlate to swim bladder volume. Additionally, the COM is always located posterior and ventral to the COB, resulting in a destabilizing pitching torque that would tend to point the snout up. Our results indicate that swim bladder volume does not affect static stability in bluegill sunfish, but those fish must constantly produce a tail up torque to maintain a horizontal orientation. Additionally, we believe that our digital COM/COB determination method can be applied to other fishes for a broader survey of static stability.