Relation between Aiming and Catch Success in Larval Fishes

The actual attack of prey by common carp (Cyprinus carpio) and northern pike (Esox lucius) larvae, lasting 5–20 ms, was described using high-speed cinematography showing synchronous lateral and ventral views. The accuracy of aiming at the prey was measured. A model comparing the ratio mouth radius/aiming inaccuracy to catch success of stationary prey accurately predicted catch success for larval carp feeding on Artemia nauplii and for larval pike feeding on Daphnia. The increase in catch success during ontogeny was caused by an increase in the ratio mouth radius/aiming inaccuracy. Maximal suction velocity in the water flow created by pike larvae (14 mm standard length) was 0.84 m/s, much higher than the escape velocities of even calanoid copepods. Nevertheless, even Daphnia could sometimes escape the suction flow by jumping away. The relative importance of aiming and speed of attack on catch success depended on prey species. Prey size seemed unimportant in determining catch success.