PORTER, Marianne E; DEAN, Mason N; SUMMERS, Adam P; University of California, Irvine; University of California, Irvine; University of California, Irvine: The role of spiracles during respiration in swimming dogfish

Spiracles in elasmobranchs are vestigial gill slits presumed to be used in respiration, though there is some evidence of a sensory function. Animals at rest have been shown to use their spiracles, sometimes in synchrony with their mouth for respiration, but it is not clear whether spiracles play a role in respiration during swimming. With increasing swimming speed there is increased oxygen demand, and we expect that ventilation rate and spiracular opening rate will be tightly correlated and both will increase with swimming speed. We measured ventilation rate in Squalus acanthias using a pressure transducer in the oropharyngeal cavity, and we simultaneously counted the number of spiracular openings in a thirty second period. We tested six animals at various speeds between 0.47 and 1.18 body lengths per second (BL/s) in a racetrack style flume. Ventilation and spiracle opening rates both increased significantly with increasing swimming velocity (F_1,144=15.755, p<0.001 and F_1,73=106.47, p<0.001, respectively). However, we found no significant relationship between ventilation rate and rate of spiracle opening. This uncoupling suggests spiracles may not be playing the same role in ventilation at low and high swimming speeds.