養魚池水溶存酸素量の日中変化と植物プランクトン密度,魚の飼養密度及び日射量との関係

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The diurnal variation of the oxygen content of the fish-culture-pond water was observed. The oxygen content was determined by the carbon dioxide method. The density of phytoplankton was estimated by means of the transparency that was determined by NAKAMURAs small white disk. (cf. the note of Fig. 1.). 1) Generally speaking, the dissolved oxygen content, throughout the year, was at minimum toward sun rise, after which an increase took place, reaching the maximum value at 2-3 hours before sun set, from then a decrease took place until the next morning (Fig. 1-5). But in the early morning, being short of the solar radiation, the decreasing tendency lasted for some time after sun rise. This phenomenon was remarkable at the bottom layer (Fig. 1. -B). 2) The higher the density of phytoplankton was, the wider the range of the diurnal variation of the oxygen content was (Fig. 1. -5). In the case of the pond water having a low density of phytoplankton, the level of the oxygen content was low throughout the day (Fig. 2.) As to the pond water containing an excess of phytoplankton, the level was extraordinarily high at the maximum and a rapid decrease took place during the night (Fig. 3.). In both cases, the fish presented symptoms of dyspnoea owing to the lack of the dissolved oxygen early in the morning. As for the pond water having a moderate density of phytoplankton, the level of the oxygen content was high throughout the day (Fig. 1. -A, B). 3) The larger the fish population was, so far as it was whithin a certain limit, the wider the range of the diurnal variation of the oxygen content was (Fig. 5. and Table 1. ). 4) There was a positive correlation between the oxygen increment and the amount of the solar radiation during the period (Fig. 6. and Table 2.).
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養魚池水溶存酸素量の日中変化と植物プランクトン密度,魚の飼養密度及び日射量との関係

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