Sucking while swimming: Evaluating the effects of ram speed on suction generation in bluegill sunfish Lepomis macrochirus using digital particle image velocimetry
Abstract
It is well established that suction feeding fish use a
variable amount of swimming (ram) during prey capture.
However, the fluid mechanical effects of ram on suction
feeding are not well established. In this study we
quantified the effects of ram on the maximum fluid speed
of the water entering the mouth during feeding as well as
the spatial patterns of flow entering the mouth of suction feeding
bluegill sunfish Lepomis macrochirus. Using
Digital Particle Image Velocimetry (DPIV) and high-speed
video, we observed the flow in front of the mouth of three
fish using a vertical laser sheet positioned on the midsagittal
plane of the fish. From this we quantified the
maximum fluid speed (measured at a distance in front of
the mouth equal to one half of the maximum mouth
diameter), the degree of focusing of water flow entering
the mouth, and the shape of the ingested volume of water.
Ram speed in 41 feeding sequences, measured at the time
of maximum gape, ranged between 0 and 25·cm·s–1, and
the ratio of ram speed to fluid speed ranged from 0.1% to
19.1%. In a regression ram speed did not significantly
affect peak fluid speed, but with an increase in ram speed
the degree of focusing of water entering the mouth
increased significantly, and the shape of the ingested
volume of water became more elongate and narrow. The
implications of these findings are that (1) suction feeders
that employ ram of between 0% and 20% of fluid speed
sacrifice little in terms of the fluid speeds they generate
and (2) ram speed enhances the total body closing speed of
the predator.