ON TURBULENCE EFFECTS ON FISH SWIMMING PERFORMANCE: A CASE STUDY OF THE NEW ZEALAND NATIVE FISH GALAXIAS MACULATUS (INANGA)

摘要

Turbulence effects on swimming performance of inanga are studied using the 'fixed velocity' (or 'fatigue') method. The study is based on laboratory experiments in two closed channels of similar geometry but with significantly different turbulence levels. The experiments and data analyses revealed no noticeable effects of turbulence on the swimming velocities of inanga. Three possible explanations for this unexpected result are suggested. The most plausible explanation relates to mechanics of fish-turbulence interactions that, in our opinion, should be scale-dependent. Briefly, within the same turbulent flow fish with different dimensions will experience different impacts from turbulent eddies. A fish of length L will probably not feel turbulent eddies smaller than (or comparable with) L, but will react to eddies appreciably larger than L. Physical considerations suggest that the turbulence impact on fish should increase with a decrease in the ratio L/l_e, where l_e is the scale of the energy-containing eddies, which are comparable, in general, with the flow size. In our experimental set-up the fish length was similar to the characteristic scales of the flow (i.e., L/l_e～1) that could 'smooth' differences in fish response to low-turbulence and high-turbulence environments. To resolve this issue future research should cover a wide range of L/l_e, fiom L/l_e 1 to L/l_e > 1.