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
The distributions of aquatic fungi in lake bottoms with anaerobic layer were observed during the summer stagnation period. The aquatic fungi were scarce both in quantity and in quality in the bottom muds. The genus Pythium and Aphanomyces were the only fungi in this season. The distributions of the aquatic fungi in the bottom mud had close relation with the amount of dissolved oxygen of the bottom water. Some experiments were carried out in the laboratory on the effect of low oxygen tension upon the fungus activity. The results were in accordance with the observations in lake bottom.
Studying on the relation between the quantities of the next three groups-eggs of fishes, larvae of fishes and plankton-collected simultaneously by a horizontal surface haul with the larval net, the following results were obtained. 1. When abundant (more than 1,000 individuals) eggs of fishes are collected, the other two groups were rather scanty : When abundant (more than 1,000 individuals) larvae of fishes are collected, the other two groups were rather scanty : and likewise when abundant (more than 200cc in settling volume) plankton are collected, the other two groups were scanty. It never happened that two or all of these three groups were collected in abundance at the same time. 2. The reverse to above mentioned relation does not hold good, two or three groups may be scanty simultaneously. 3. When the eggs of the fishes (or another group) are collected in abundance fully, in the general case, one special species of the group among it was extremely dominant. Considering the above mentioned facts, it is supposed that the mechanisms of the formation of patches (the dense swarms) are different according to the eggs of the fishes, larvae of the fishes or to the plankton. The patches of these planktonic or semi-planktonic organisms are not due only to the mechanical actions of the external force, but also to the reactions and behaviours of the organisms in various ways according to the species.
As shown in Table 1,116 individuals of young Minous monodactylus from 10 stations and seven individuals of young Erisphex potti from five stations had been collected by the horizontal surface hauls with the larval net, during the period from 1953 to 1960. The tows of the larval net had been repeated 1271 times. The period of occurrence of these juveniles covers most part of the year, and the range of surface water temperature and chlorinity in which they occur is rather wide. But neither young Minous monodactylus nor young Erisphex potti occurred when the chlorinity exceeded 18.9 per cent. In spite of the above mentioned fact, the locality (the sea area of occurrence) of the young of both species was limited to a restricted area of the northern part of the East China Sea. It was found that all stations where the young of these two species were collected are situated in the cold water mass originating in the Yellow Sea and descending southwards into the northern and central parts of the East China Sea. It is supposed that one of the principal grounds of spawning and nursery exist in this cold water mass. The time of occurrence were all in the night ranging from 20 : 20 to 05 : 20,and the depth of the stations where the young were caught is shallow ranging from 40m to 94m. It seems that these young live in the sea bottom in the daytime, and take to pelagic life at night.
The food of a fresh-water goby, Rhinogobius similis GILL, was studied in the River Ukawa during the summer and the autumn of 1958,with the following results. This fish is able to feed on the bottom insects as well as on the algae, and the stomach contents change in accordance not only with the composition and amount of food substances but also with the abundancy of the dominant fish, Plecoglossus altivelis, in the habitats. The amount of insects taken by female adults of 6.5〜8.5cm in total length was estimated to be about 0.1 gramme(wet weight)per day, when fed exclusively on the bottom insects in July.