Prey Capture in the Largemouth Bass

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The behavior of the largemouth bass, Micropterus salmoides, during prey capture was studied with high-speed cinematography. Differences in the pattern of approach to prey indicated that the bass distinguished different types of prey and whether the prey was on the bottom or in mid-water. The distance from the prey at which the final attack was initiated was greater when the bass was traveling toward the prey at a higher velocity. The allowable error in this initiation distance was about one-fourth the length of the bass's head. Attacks initiated beyond this margin of error usually failed. About 10% of all filmed attacks failed. Once the jaws began to open the sequential movements of the head elements appeared to be completely determined. Two different patterns were observed, however, depending on whether the bass swam over the prey or drew the prey toward itself, i.e., suction feeding. Rationalization of these differences is presented. During suction feeding, the usual alternative, the jaws were opened before there was appreciable expansion of the mouth cavity. The asymmetry between opening and closing movements was also important; for without differences between them the prey would be expelled as the jaws closed. The additional velocity of the upper jaw due to protrusion of the premaxilla was measured. This additional velocity was relatively greater for smaller bass and in the slower-moving attacks of the same fish. The significance of this additional velocity in the evolution of the protrusible upper jaw of fishes is discussed.