70.2 Jan. 7 Evidence for passive suction feeding in Pacific Bluefin tuna, Thunnus orientalis BAHLMAN, Joseph Wm*; WAINWRIGHT, Peter C.; Brown University; University of California at Davis Joseph_Bahlman@brown.edu
Suction feeding is the most widespread and commonly used mechanism of prey capture in teleost fishes. In all described examples, this behavior involves the rapid expansion of the mouth and buccal cavity, generating suction, and causing water and prey to flow in through the mouth aperture. We used video to record Pacific Bluefin tuna at the Monterey Bay Aquarium, in Pacific Grove, California. We obtained 19 lateral view video sequences of tuna feeding. In each sequences, we tracked the movement and calculated velocity for the tuna, the prey, and tuna’s mouth aperture. Suction was shown by the acceleration of prey towards and into the tuna’s mouth. Buccal expansion was shown by changed in mouth aperture size, and the dorsal-ventral depth of the head. 5 sequences displayed suction associated with a clear buccal expansion. The remaining 14 sequences show the tuna swimming with their mouths held continuously open, and still generating significant suction without any visible buccal expansion. More detailed kinematic analysis shows the magnitude of the suction generated is positively correlated with mouth aperture size and swimming speed. In some feedings the magnitude of suction generated by swimming with their mouth held open is greater than suction generated in sequences that involve buccal expansion. We propose a mechanism for passively generating suction (without rapid buccal expansion) via a pressure gradient between the opercular opening and the mouth aperture caused by accelerating flow around the tuna’s body. We suggest that higher flow velocity at the opercular opening relative to the mouth aperture may induce a flow of water through the buccal cavity that the tuna uses to suck the prey into its mouth during ram feeding.