Diurnal changes of gas bladder and behavior of postlarval anchovy and other related species

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  • カタクチその他イワシ類シラスの鰾と生態について
  • カタクチ ソノタ イワシルイ シラス ノ ヒョウ ト セイタイ ニ ツイテ

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Abstract

Postlarval anchovy showed a definite change in the shape of its gas bladder between day and night. Such diurnal changes appeared in the sardine and round herring too. Major points of interests are summarized as follows:<br> 1. Gas bladder of the postlarval anchovy, over 7.1 mm in total length, appeared shrinking throughout the day.<br> 2. A ratio of different sized gas bladders indicate that it takes about one hour for the fish to expand and shrink the bladders. Volume of the bladder is approximately pro-portional to 3.6 times the total length.<br> 3. Changes in the gas bladders may not be always indispensable for controlling depth of the swimming layer. But, these may contribute to regulating its specific gravity and also to holding the balance of the fish.<br> 4. The shape of gas bladders of elongated postlarvae may affect hydrostatic resistance of the body. Thus, the larvae may increase their activity during day when the body becomes slender. At night, the fish may remain still, stop feeding and break up the composition of the school. Such thinning of density may be effective for reducing mass predation on the postlarvae at night.

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