北西オ-ストラリア海域産マグロ・カツオ類稚仔の食性〔消化管内容物の魚種間の差異-1-〕

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Gut contents of a total of 4159 larvae of albacore, yellowfin tuna, bigeye tuna, southern bluefin tuna, skipjack and frigate tuna collected in the area northwest of Australia from Oct. 1977to Jan. 1978, and from Dec. 1978 to Mar. 1979, were examined. The results obtained are as follows. 1. Gut contents of tunas and those of skipjack and frigate tuna are noticeably diddferent in the composition of food elements: Four species of tunas feed generally on the Copepoda and other zooplanktons in nearly equal numbers or slightly more Copepoda, whereas skipjack and frigate tuna Appendicularia and Evadne. 2. Ivlev's electivity index indices suggest that the difference in the food composition between the above two groups of larvae could be attributable to the difference in their feeding habit on prey organisms, not to the plankton composition in their habitats. 3. Individual gut contents of four species of tunas are mainly small ones of 0.21-0.80mm body length. Gut contents of skipjack and frigate tuna, however, comprise a large quantity of those exceeding 0.81mm body length.
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