The Response of Fish to Shearing Surfaces in the Water
The particular problem of the mode of functioning of the louver screen, used in deflecting fish from water intakes, led to a study of the response of fish to shearing surfaces in the water and of their behaviour in the presence of model screens generating such surfaces in the neighbourhood of the slats.
A variety of species of freshwater fish were shown to respond by turning towards a higher velocity flow when passing through a shearing surface, although migrating salmon smolts did not do this with any regularity. The magnitude of the effect was directly related to the velocity differences encountered and it was only forthcoming when the fish moved head first through the shearing surface. A marked response was produced by even extremely low velocity differences.
The hydraulics of model louver screens were studied; showing the occurrence of rotating columns of water between the slats and of shearing surfaces in these regions in such a form that fish might be expected to respond to them. Such model screens were shown to be effective in deflecting fish in the laboratory and their efficiency was related to the velocity of water flow, width of slat gap and size of fish.
Behavioural studies of fish in front of such screens showed responses that could be interpreted as arising from the shearing surfaces between the slats. The major contribution towards the deflection of fish would, however, seem to come from a purely mechanical response to the form of the flow lines in front of the screen. These tend to divert the fish into the by-pass whether the approach is head first or tail first. Visual response to the screen was shown to be unimportant.
Experiments with anaesthetized fish showed that these were deflected as effectively as live ones and in some cases even more so. It seems possible that live fish may resist physical movement in the streamlines but it is also clear that an active response to the screen and its associated water flow, by such live fish, is an important element in the successful functioning of louver screens.
KeywordsLive Fish Visual Response High Velocity Flow Salmon Smolt Vortex Circu
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- Lowenstein, O. 1957 The acoustico-lateralis system. In Physiology of Fishes, 155–86, New York, Academic Press Inc.Google Scholar