Age Composition, Sex Ratio, Growth, and Feeding Habit of Native and Introduced Hatchery-Reared Lake-Run Masu Salmon, Oncorhynchus masou masou in a Japanese Mountain Reservoir.

YAMAGUCHI Kazuhiko, NAKAMURA Tomoyuki, MARUYAMA Takashi

doi:10.11233/aquaculturesci1953.48.615

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Other Title

人工湖における降湖型サクラマス，Ｏｎｃｏｒｈｙｎｃｈｕｓ　ｍａｓｏｕ　ｍａｓｏｕの天然魚と放流魚の年齢組成，性比，成長，食性
ジンコウコニオケルコウコガタサクラマス 0ncorhynchus masou masou ノテンネンギョトホウリュウギョノネンレイソセイセイヒセイチョウショクセイ

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Abstract

We studied the age composition, sex ratio, growth, and feeding habit of native and introduced hatchery-reared lake-run masu salmon, Oncoyhynchus mason masou, in the Yashio Reservoir, which is at the upper Kinu River, Tone river system, from March to August 1992 and from April to August 1993. Native salmon were composed of ages 1⁺ and 2⁺ fish and introduced hatchery-reared salmon were composed of only 1⁺ fish. The sex ratio was biased toward females in both types of salmon. For native 1⁺ females in 1993, body length and weight did not increase from April to August, and their condition factor in the summer (June to August) was lower than in the spring (April to May). The gonad somatic index hardly changed from March to July and increased from July to August. The stomach contents of both salmon types were almost entirely smelt, Hypomesus transpasificus nipponensis. The body size of both types of salmon was smaller in the Yashio Reservoir than in other reservoirs. Low growth and small body size may be caused by the low abundance of smelt and other small fishes inhabiting the Yashio Reservoir.

Journal

Aquaculture Science

Aquaculture Science 48 (4), 615-622, 2000

Japanese Society for Aquaculture Science

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