Meeting Abstract
Elasmobranch ventilation is a two-pump system driven by the generation of a pressure differential between the oral (mouth) and branchial (gill) chambers. Early work conducted in Squalus acanthias evaluated the pressures generated in each of five gill chambers and found there to be a phase-shift in timing but no difference in pressures generated by each gill. Therefore, work on ventilation in a variety of elasmobranch species has since assumed that each chamber generated equal pressures. We reevaluated this idea by implanting pressure transducers into gill chambers two, three, and five (numbered anterior to posterior) of Squalus suckleyii (n=5) across a range of sizes, and found there to be a significant difference in the amplitudes of pressure generated between gills (p<0.0001). A Tukey test indicated that gill two was higher than gill three (p<0.0001) and gill five (p<0.0001), and gill three was higher than gill five (p<0.0001). Size of the individual (body length) was also found to have a significant effect on the amplitudes generated in each gill slit (p<0.0001). Linear regressions of amplitude relative to size for each gill chamber showed that pressure in gill two and three scales with size, but gill five does not (p=0.249). Differences in our findings from studies previously conducted may be a result of updated technology, or as a consequence of Squalus suckleyii having multiple ventilatory modes in which the gill chambers are used differentially, as has been observed in species such as the hedgehog skate. This observed attenuation of pressure can potentially shed light on the pattern of a reduction in the number of gill slits over evolutionary time.
