The effect of prey type on the predatory behaviour of the fifteen-spined stickleback, Spinachia spinachia (L.)

The fifteen-spined stickleback, preying on the mysid, Neomysis integer, and the amphipod, Gammarus locusta, maximized its energy intake by adjusting its predatory behaviour to the prey being attacked. The escape speed of Neomysis placed an upper constraint on the size of the prey available to fish of a given size. The increase in importance of Neomysis in the natural diet of larger sticklebacks reflected size-dependent limitations of the fast-start performance in these fish. The escape speed of Gammarus did not limit its availability to the sticklebacks; the limiting factor for this prey was its cross-sectional area. The fish expended 20 times more energy attacking Neomysis than Gammarus, but Gammarus took up to 159 times longer to ingest. Neomysis always responded to an attack with a tail-flip, which usually resulted in movement at an angle of approximately 90° to the direction of attack. Although Gammarus occasionally used a tail-flip response, it was never used to escape a fish attack. Adoption of a stationary C-shape often deterred the fish from attacking Gammarus.