HORNSTRA, H. M.*; HERREL, A.; MONTGOMERY, W. L.; Northern Arizona University, Flagstaff; University of Antwerp, Belgium; Northern Arizona University, Flagstaff: Gas bladder movement in lionfishes: a novel mechanism for control of pitch

Lionfish (Pterois volitans) are crepuscular reef predators that stalk their prey and often hover just above the reef, maintaining unique body positions with little apparent fin movement. They posses bilaterally symmetrical muscles that originate on the skull and insert on the gas bladder, but these muscles appear not to be sonic in function as in most fishes with similar muscles. We hypothesized that these muscles induce changes in gas bladder position within the fish, thus changing the center of buoyancy and allowing for pitch changes. We investigated the role of the gas bladder as an aid in postural control by examining gas bladder movement within P. volitans using a high-speed digital cineradiographic system. Two lead markers were inserted just below the dorsal fin to serve as reference markers for body position. Lionfish were then induced to pitch head-up or head-down in response to prey. Pitching behavior and gas bladder movement were recorded and three angles were calculated: 1) the angle between the main axis of the body and the horizontal, 2) between the main axis of the gas bladder and the horizontal 3) between the main body and gas bladder axes. As the fish pitched head-up, the angle between the gas bladder and the body increased whereas when the fish pitched downward this angle decreased. This suggests that lionfish move their center of buoyancy forward of their center of mass by shifting the gas bladder within the body cavity, allowing for a change in body pitch and fine-tuning of position. Although further research is still needed, it appears that the muscles associated with the gas bladder may provide P. volitans with a novel mechanism for pitch control.