How fish power suction feeding.

If you go fishing and cast your lure out across a pond, settling it skillfully by the lily pads, you may see the water drop out from under your bait with a sucking whirlpool as you engage with the most popular sport fish in the world, the largemouth bass. Almost all popular recreational sport fish species (bass, salmon, trout, pike, grouper, snapper) feed by attacking their living prey with powerful suction, expanding their mouth and pharynx rapidly to suck the prey in before biting down and swallowing. This behavior is of great interest to scientists and recreational fishers alike because it is a dramatic, predatory event (Fig. 1) that is at the crux of survival for both predator and prey. It involves a complex system of bones and muscles to expand the head, is a widespread and ecologically successful strategy among aquatic animals, and is a major source of the excitement and allure of recreational fishing, one of the largest and most effective economic engines for environmental conservation of freshwater and marine habitats. In addition, suction feeding has been challenging to understand from the perspective of biomechanics (the study of how organisms work) because it is such a fast and complex behavior. In PNAS, Camp et al. (1) report a major advance in our understanding of how suction feeding works, using cuttingedge imaging technology and analyses of muscle mechanics to identify the source of the power that drives suction feeding in our feisty friend from the pond, the largemouth bass. Suction feeding is the primary mode of prey capture in fishes (2, 3), a method used to draw prey into the mouth by using the density of water as a tool for prey transport (Fig. 1). Suction feeding behavior has been the focus of numerous studies involving high-speed video analysis of kinematics (4, 5), electromyographic study of the motor patterns that drive suction feeding (6, 7), and application of a range of techniques, such as pressure transduction (8, 9), sonomicrometry (10), and digital particle imaging velocimetry (11). These studies have discovered the timing of different aspects of cranial kinesis involved in suction feeding, revealed the patterns of muscle contraction underlying suction generation, and measured the hydrodynamics, changing water pressure, and suction velocity during feeding. As a result, we have a detailed understanding of the morphology, behavior, and biomechanics of one of the fastest and most widespread feeding behaviors among vertebrates. However, the sources of power for this explosive behavior have remained poorly understood. It takes a lot of power (force × velocity) to move water fast for suction feeding, and the source of that power is muscle contraction. Fish heads are packed with muscles for jaw opening and closing, rotating and flaring bones for breathing and feeding, and muscles in the pharynx for swallowing and controlling the gills. However, the key to powering large suction forces is high muscle power during jaw opening, and the biggest muscles in the head, the biting jaw adductor muscles, are for jaw closing and thus cannot power suction. So whence does suction power come? The intriguing answer, arrived at over years of Fig. 1. Skull morphology and strike mechanics of the large-mouth bass,Micropterus salmoides. (A) Skeletal morphology of the largemouth bass, with red arrows indicating primary muscle force vectors, and blue arrows showing movements of bones during the opening phase of suction feeding. (B and C) Rendered frames from an XROMM animation of a sample strike before the onset of expansion of the mouth (B) and just before peak gape (C). (D–G) Suction feeding in the largemouth bass Micropterus salmoides. Simultaneous lateral (Left) and ventral (Right) views show the role of lateral expansion in prey capture by suction. From time 0–8 ms cranial elevation and mouth opening occur before contact with the prey item. At 16 ms the maxilla is observed in anteriorly rotated position and expansion of the head and suction forces are near peak. At time 24 ms the prey is being sucked into the mouth, after which the jaws close on the food item within about 50 ms (or 1/20 of a second). Images B and C courtesy of Ariel Camp (Brown University, Providence, RI) and ref. 20. Author contributions: M.W.W. and A.M.O. wrote the paper.