Prey Capture By Fish Larvae, Water Flow Patterns and the Effect of Escape Movements of Prey

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Abstract
We present a hydrodynamic model of suction feeding of a 6.5 mm carp larva, calculated from the streamlines and fluid particle pathlines observed. From this model we also have calculated the accelerations of the water near the mouth aperture (which reach 800 m/s2) and the path lines of actively accelerating fluid particles (which mimic 'escaping prey'). The shape of the parcel of water sucked into the mouth cavity is almost spherical, due to the prevalence of suction flow over swimming velocity. This parcel of water is entirely in front of the initial position of the larva. We suggest that the low velocity of swimming and the absence of protrusion of the mouth are func- tionally coupled with the high inaccuracy of aiming of young fish larvae. For a prey starting in the centre of this parcel of water the best direction for escape is forward. The velocity required for escaping radially is twice as high as for escaping forwards. Optimum sucking techniques for fish larvae are discussed.

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