By Wen-Hwa Kwain, Hugh McCrimmon
Animal Behaviour, Volume 15, Issue 1, January 1967, Pages 75-78, ISSN 0003-3472, DOI: 10.1016/S0003-3472(67)80014-9.

Abstract: Summary
Fingerling trout when exposed to the series of white light intensities over a uni-coloured bottom of either black or white were randomly distributed over the bottom. While yearling trout were similarly randomly distributed over a black background, when held over a white background they exhibited a preference for the edge of the tank, distributing themselves randomly about its periphery.
When exposed to a choice of black or white bottom colouration, the fingerling trout exhibited no preference for either black or white under the series of test intensities of artificial daylight. The yearling trout, however, showed a significant preference for the black bottom at a low light intensity only, but not at higher intensities

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