魚の摂餌に関する生態学的研究-III

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It has been found1, 2) that a relatively constant value for the satiation amount can be obtained with a well acclimatized school of fish. In the present investigation, the effect of the time of food deprivation on the satiation amount, the digestion of food in the stomach, and the relationship between the digestion of food in the stomach and the satiation amount, are examined. The results obtained are summarized as follows: The satiation amount of a school of fish depends on the degree of hunger. As the time of food deprivation increases, the satiation amount first increases and then levels off to a constant value (Fig. 1). Further, when the time of food deprivation is extremely long, about 10 days, the satiation amount does not exceed the constant value but the amount rather decreases (Fig. 2). At the beginning of satiation the amount of food in the stomach sharply decreases. This rate of decrease levels off in later stages and a considerable time elapses before the stomach is completely empty (Fig. 1 and Table 3). If undigested food remains in the stomach, the state cannot be referred to as being complete hunger. Until the food in the stomach is completely digested, the satiation amount varies inversely with the amount of undigested food in the stomach. The satiation amount reaches its peak value as the stomach contents approach zero. Since the capacity of the stomach is limited, the satiation amount after reaching its maximum at the state of complete hunger maintains this maximum value even when the time of food deprivation is further extended for a short period of time (Fig. 1).