A Quantitative Hydrodynamical Model of Suction Feeding in Larval Fishes: The Role of Frictional Forces

A model is presented for the suction flow during prey intake by larval fishes. With the model it is possible to calculate the influence of friction on suction by larvae and the power and energy used during suction. The mouth cavity is depicted as an expanding and compressing cylinder (`profile'). Unsteady and viscous effects are taken into account. The expansion of the profile was prescribed in such a way that the volume flow of the profile was almost equal to the volume flow of a carp larva as measured from a 1100 f.s ^-1 film. For a 6.5 mm carp larva, calculated maximal power delivery during the strike is 7 μ W (13 W per kilogram muscle) and total energy 20 nJ. At the time of maximal water velocity (t = 5 ms) only 40% of the total delivered energy is present at kinetic energy, so 60% of the energy is lost to friction. The calculated pressure inside the mouth cavity is independent of radial position, except very near the mouth aperture. As the model also calculated the velocity field of the water around the head of the fish larva, it was possible to calculate the paths of actively escaping prey. Through variation of parameters, critical factors in the escape reaction of the prey from the suction flow of a fish larva can be recognized.