A mechanical perspective on suction feeding in fishes.

Suction feeding in fish has long fascinated experimental biologists because of its complex motions, intricate anatomy and vast distribution across thousands of species and nearly every aquatic habitat. Suction feeding poses three main mechanical challenges for fish. First, how do shortening muscles create three-dimensional (3D) expansion of the mouth cavity to suck in water? Second, how do muscles produce the substantial power required for fast and forceful expansion to accelerate food and water into the mouth? Third, how is water moved through the mouth so that food can be deposited in the oesophagus? Over the last 15-20 years, new methods for measuring and modelling bone, muscle and fluid motions have advanced our understanding of how fish meet these three mechanical challenges of suction feeding. In this Review, we examine these advances, primarily through the lens of mechanical power, and highlight understudied areas with exciting new questions. We discuss how skeletal levers and linkages transform and transmit muscle force into 3D mouth cavity expansion. We explain how the power for rapid and forceful expansion is generated primarily by large regions of the body muscles - although, for all feeding muscles, power output depends on how much and how fast the muscles shorten. Finally, we outline the key characteristics of flows outside and inside the mouth, and their implications for food capture and transport. Future research into the interactions of skeletal motion, muscle function and water flows will reveal new insights into suction-feeding morphology, evolution and ecology.