漁網の色に関する研究-II : 着色網地に対する魚群の行動及び魚群の網目通過について

概要

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Two pieces of different coloured nets were combined with one another side by side and set stretched in an outdoor pool (length, 26m; width 5m; depth 1.5-O.7m). The behaviours a school of rainbow-trout, Salmo gairdnerii irideus (GIBBONS) takes in the neighbourhood of the net were observed, the results obtained being summarized as follows: 1. In so far as a large difference in the number of fish passing through is detectable between the individual pieces of net, the fish school behaves quite specifically according to the sort of colour of the net. 2. The colours of net examined were red, orange, yellow, green, and blue; and effectiveness of these colours in the fish passage increased in the order: green>blue>yellow=orange> red. Thus, relative passability for fish estimated for individual nets on the basis of green net varied with the dominant wave length of the reflected light. 3. No marked difference is detectable between the curves drawn for the distribution of light spectrum in the pool water on the one hand and for the relative intensity of the light reflected respectively from blue and green nets on the other resembles one another closely. This suggests that the weak barring effect of a blue or green net against fish passage may well be attributed to the weakness of contrast made by these nets to their surroundings.