Reduction of transport stress of ayu by obligated schooling |
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Authors: | KEI'ICHIRO IGUCHI FUMINARI ITO KOGI OGAWA NAOTO MATSUBARA TAIGA YODO TSUGIKO YAMASAKI |
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Affiliation: | ;National Research Institute of Fisheries Science, Fisheries Research Agency, Ueda, Nagano 386-0031, ;National Research Institute of Aquaculture, Fisheries Research Agency, Nansei, Mie 516-0193, ;Faculty of Fisheries, Nagasaki University, Nagasaki, Nagasaki 852-8521 and ;Japan Science and Technology Corporation, Domestic Research Fellow, Ueda, Nagano 386-0031, Japan |
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Abstract: | We investigated stress responses of ayu Plecoglossus altivelis under the hypothesis that overcrowding during transport can be a stressor and the stress predisposes fish to disease by decline in immunocompetence. The extent of stress response was determined under different fish densities. As inferred from the serum concentration of cortisol 1 day after the treatment, the density at more than 23 kg/m3, which was within the range of normal transporting procedures, acutely evoked intense stress responses. To examine a possible way to reduce the stress response of fish under crowding conditions, we compared two fish groups established in water tanks with circulating (whirling) and turbulent currents at the same density. The cortisol levels 1 day after the treatment were 2.5-fold higher in turbulent current than in whirling current. Fish in whirling current formed a school, while those in turbulent current aggregated with each other. Schooling of fish induced by water flow may reduce their stress responses during transport. A transport system with a directional water flow should keep fish in good condition without reducing the number of fish contained. |
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Keywords: | circulating (whirling) water coldwater disease cortisol obligated school Plecoglossus altivelis transport stress |
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