DOLCE, JL*; WILGA, CD; University of Rhode Island; University of Rhode Island: Gill Slit Kinematics in Suction and Ram Ventilating Sharks

The movement of the gill slits during suction and ram ventilation in elasmobranchs differs mechanistically. The gill slits remain open during continuous swimming in ram ventilation. In suction ventilation, the gill slits open for the compression pump phase and close for the suction pump phase. The slits are generally considered to be one functional unit, regardless of ventilation mode. Individual gill slit kinematics of suction and ram ventilators have not been compared previously to evaluate these mechanistic differences. In this study, we quantify the gill slit kinematics at rest in white spotted bamboo sharks, Chiloscyllium plagiosum, a suction ventilator, and bonnethead sharks, Sphyrna tiburo, a ram ventilator. The peak opening width of each slit and time to peak opening was quantified using high speed video. During ram ventilation in bonnethead sharks, no difference in opening width among the gill slits was found. Furthermore, the slits are continuously held open while swimming. During suction ventilation in bamboo sharks, the peak opening width of slits one and two was smaller than the peak opening widths of slits three through five (p<0.05). Slits three through five reached their peak opening width at least 20 milliseconds earlier than slits one and two. Larger opening widths and shorter time to peak opening in gill slits three through five could imply those slits pass more water than slits one and two. These data suggest that the gill slits and arches of suction ventilators may be separated into at least two functional units that play different roles in ventilation. Future studies will investigate the presence of multiple functional units of the gill arches and slits for other suction ventilators and compare the mechanics of suction ventilation to the mechanics of ram ventilation.