Ventilation of Spiny Dogfish (Squalus suckleyi): Are These Five Gill Slits Working Together?

Abstract

Shark’s ventilation has long been characterised by a two-pump model, where the water coming from the spiracle and the mouth is released by the gill slits after the breathing process. This movement is created by the difference of pressure between the oro-branchial cavity and the parabranchial cavity, consisting of five gill pouches. In an attempt to compare the actual flow velocity coming from each of these five gill openings, experiments have been made on seven individuals of spiny dogfish, Squalus suckleyi. External measurements have been taken, revealing important differences between the fifth gill slit and the four others, in term of vertical length and width. Also, the introduction of dyed water just above the spiracle has revealed the utilisation of the four first slits. A particle image velocimetry analysis have confirmed the weak flow coming from this last slit. It has also exposed the possibility of the fourth slit’s flow being less than the flow coming from the three first gill openings. This could be in relation with their feeding behavior, which mostly consist in suction action. The fifth slit could then be used to discharge water while the shark is feeding on preys.