On the Food of the Salmonoid Fish, Ayu (Plecoglossus altivelis Temminck & Schlegel). III

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In the present paper, the writers report the foods of Ayu collected at Corea and Formosa, and the peculiar food habit of the adult fish. The samples from Formosa we examined were chiefly diatoms and bluegreen algae mixing with minute sand grains and some kinds of green algae. And, rarely some protozoa as Diffugia sp. were also found. The Corean samples we examined were mostly diatoms and desmids, and several kinds of green and bluegreen algae were found. Adding these algae pretty many minute sand grains were also mixed. From these results we may say, therefore, that the characteristics of these foods consist in the existence of several kinds of desmids, which we have never been met with so'much in the food of the adult Ayu in any other localities. In the previous paper, we reported that the food of adult Ayu are entirely vegetative matters, but from the subsequent studies, we perceived that in some peculiar cases Ayu takes animal matters still it grown up to the adult stage. Namely, it takes the larvae of Asellus aquaticus (Linné), baetidae, hydropsychidae and chromidae as food. But, from our observation, this phenomenon is a very rare exceptional case caused by the peculiar conditions of the river. And the general appearance of this Ayu shows plump shape just as we often experience in the cultured ones which was fed by the animal matters in the artificial ponds.
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