郡山金魚養殖池における水色の発現機構と金魚の生産 : 5 異なる藻類相が, 金魚に対する環境条件としてもつ意味に関する研究

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Gold-fish culturing ponds were calssified into two types, i.e. type A and type B from chromatological and biological points of view ; their characteristics can be summarized as follows (1961) : Type A ponds : The production of Chlorophyceae exceeds that of type B ponds throughout the year. Chlorophyceae becomes dominant, overwhelming cyanophyceae in June and in winter. By such a characterlistic of seasonal change of plankton. the Jocate points x, y, of the water color approaches to the Illuminant C twice a year on the C.I.E. chromaticity diagram. Type B ponds : The production of Cyanophyceae exceeds that of type A ponds throughout the year. Chlorophyceae becomes dominant only in winter. Therefore, the locate points x, y, of the water color approaches to the Illuminant C once a year, i.e. in winter. It was made clear that the production of Fringetail gold-fish in the first year was larger in the type A ponds than those of type B (1961). To make clear why the production of Fringetail gold-fish is larger in the type A ponds than in type B ponds, I have carried out the following experiments from the view point of environmental sanitation of the gold-fish. (1) The experiments on the difference of the vertical distribution of dissolved oxygen and the standing crop of phytoplandton between the two types of ponds. (2) The experiments on the difference of the diurnal change of the vertical distribution of dissolved oxygen and water temperature between the two types of ponds. These experiments were carried out in june, 1960,because the environmental differences between both ponds types are most remarkable in this period of the year. The results of the experiments (1) are shown in Figs. 1 and 2,in which the former shows the vertical distribution of the amount of dissolved oxygen which differs considerably in the different types of ponds. In the type A ponds, the oxygen curves are represented by hyperbola or sigmoid, while they are parabola in the ponds of type B. This may be caused by the difference of vertical distributions of the quantities of phytoplankton, as shown in Fig. 2. In the ponds of type A, the standing crop of pohytoplankton is nearly equai in quantity from the upper layer to the lower, and the absolute quantities are less than in the ponds of type B (Fig. 2). Since the light penetrates reiatively deep into the water in the ponds of type A, the productive layer is thick, and there occurs thick over-saturation of dissolved oxygen which diffuses toward the middle or deeper layer. The sudden decrease of the amount of dissolved oxygen below the middle layer is due to the decomposition of organic matter and the formation of a large amount of ooze, so that the deeper layer may be regarded as a decomposition layer, whose range is but small. In the ponds of type B, the standing crop of phytoplankton in the upper layer is considerably larger than that of the deper one. The absolute quantities are much larger in the ponds of type B than in the ponds of type A. The light is intercepted by the plankton as well as by the neuston (the neuston is more significant), the photosynthesis decreasing quickly with the increase of the depth of water, in spite of the great population throughout the water mass. The dissolved oxyen in the upper layer is extremely large but decreases suddenly with depth. The range of the production layer is very small but that of the decomposition layer is large in the ponds of type B. The results of the experiments (2) are shown in figs. 3 and 4. The curves in Fig. 3 show hyperbola or sigmoid which represent the vertical distribution of dissolved oxygen in the pond of type A in the day time, similar in Fig. 1; and, in the pond of type B the curves in the day time are all parabola. At night, however, the amount of dissolvd oxygen becomes nil from the surface to the bottom in both types of ponds, the diminishing duration in the pond of type B being much longer than in that of type A. The vertical distribution of disso