<p>The food uptake of larval carp and pike is described from high speed movies with synchronous lateral and ventral views.<p>During prey intake by larval fishes the velocities of the created suction flow are high relative to their own size: 0.3 m/s for carp larvae of 6 mm.<p>Starting from the first feeding carp larvae have morphological adaptations to suction feeding: the suspensorium and opercula can be abducted, the hyoid lowered, the mouth edges can be sealed by a rotating maxillary and the opercular keeps the opercular slit closed till the moment of prey uptake.<p>A model has been extended to calculate catch success of larval fishes from aiming inaccuracy (article 3). The absolute aiming inaccuracy (mm) increases during growth, the relative aiming inaccuracy (relative to the standard length) decreases. No causal relation exists between catch success and prey size (unless the prey is too large to pass the mouth aperture)<p>During the time fish larvae cannot yet aim accurately, they must suck the water undirectedly. By swimming and protrusion a directed field of flow is created. Both are thus unfavorable in this respect, but they are the best ways to catch prey from larger distances. Film analysis showed that protrusion is absent in 6 mm carp larvae, but already 3.8% of the head length in 9 mm larvae. Young larvae have a larger relative increase (to body weight) during suction feeding than adult fishes. This is an optimization of suction feeding by enlarging the volume flow.<p>A quantitative hydrodynamical model of suction feeding by larval fishes has been made. In the model the mouth cavity is treated as an expanding cylinder. the flow in and around the cylinder is calculated by numerically solving the Navier-Stokes equation in 2-D. Energy costs of suction feeding by larval fishes are negligible compared to the gains: 0.01% for large prey and 10% for very small prey. In an optimal foraging model energetic considerations during suction will be unimportant.<p>The relation between muscle tension required for suction and fish size is determined. The relation between duration of the suction process, as measured from high speed films from 12-485 mm pikes, was used as input. The required muscle tension appeared to be minimal at hatching and increased with increasing size. Also at sizes smaller than hatching the calculated tension increased (with decreasing size), but the slope was much weaker. So on the basis of this relation no minimal size for the use of suction feeding seems to exist, at small size a freedom for architectural changes seems to be present.<p>The interaction between suction flow and active escape movements of the prey determine which types of prey can be caught. For young larvae it is more important to postpone the moment of detection by the prey, than to maximize the water velocity. If the snap lasts longer (e.g. 20 ms) the velocity is important. The reason is that it takes 10 to 20 ms for a copepod or cladoceran to reach maximal velocity.<p>During suction by carp larvae enormous accelerations of the water do occur (800 m/s <sup><font size="-1">2</font></SUP>in the mouth opening of a 6 mm larva). If a prey enters this region of high accelerations it is impossible to escape.
|Qualification||Doctor of Philosophy|
|Award date||19 Sep 1986|
|Place of Publication||Wageningen|
|Publication status||Published - 1986|
- feeding behaviour