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KMID : 0894520200240030215
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Development & Reproduction
2020 Volume.24 No. 3 p.215 ~ p.224
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Differential Seawater Adaptability in Three Different Sizes of Under-yearling Steelhead Trout
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Lee Myeong-Seok
Lee Jang-Won
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Abstract
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Seawater adaptability of steelhead trout increases along with the increase in the size of the fish, independent of parr-smolt transformation. Three 96 h seawater challenge tests were conducted to determine the size at which seawater adaptability of steelhead trout develops. Plasma Na+ and Cl? levels, moisture content, gill Na+ /K+ ATPase activity, and mortality during the 96 h after direct transfer to seawater (32 ppt) were determined. Plasma Na+ and Cl? levels in 50 g fish continuously increased during the 96 h after the transfer to seawater (p<0.05), but the levels in 100 and 150 g fish leveled off after 24 h (p<0.05). Both 100 and 150 g size steelhead trout maintained muscle moisture content (%) better than 50 g size fish (p<0.05). Gill Na+ /K+ ATPase activity in the 100 g size group increased in a timedependent manner after transfer to seawater (p<0.05), whereas activity in the 50 and 150 g sizes did not increase (p>0.05), for which a possible explanation was discussed. A mere 2.6% mortality in both the 50 and 150 g size groups was observed. In conclusion, the current results indicate that 50 g size steelhead trout did not show development of a high level of hypoosmoregulatory capacity, whereas fish in the 100 and 150 g size groups showed a high level in our experimental conditions. Therefore, the steelhead trout larger than a 100 g size is recommended for transfer to seawater culture.
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KEYWORD
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Steelhead trout, Seawater adaptation, Osmoregulatory capacity, Na+ /K+ ATPase activity, Plasma ion levels, Muscle moisture
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