In the present paper, clover-extract as a culture medium is studied from physiological standpoints.
Daphnia does not take clover-extract directly, but unicellular organisms, especially
Scenedesmus cultured in it, are taken in as food. At first, clover-extract is decomposed by bacteria within the course of a week, at 20°C, and NH
3, CO
2, and other low molecular substances are formed, and these are utilized by
Scenedesmus. Then,
Daphnia can feed abundantly on
Scenedesmus.
Daphnia is restricted to the pH ranging from 6 to 9. Therefore, the death-rate of
Daphnia, feeding upon
Scenedesmus in the water, to which clover-extract was not added, increases when its pH-value rises above 9, due to the photosynthesis of
Scenedesmus. On the other hand, clover-extract itself does not show any effect on the mortality of
Daphnia, in view of the fact that the pH of clover-extract remains below 8, as CO
2 is given off from bacteria in spite of the consumption by
Scendesmus at the photosynthesis.
Daphnia can live at a low oxygen content, even less than 2c.c/I, remaining unaffected by the oxygen consumption of bacteria in clover-extract.
From the physiological points of view as mentioned above, clover-extract is a convenient culture medium for
Daphnia and
Scenedesmus.
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