1Kochi Prefectual Freshwater Fisheries Center, Tosayamada, Kochi 785-0016, 2Department of Aquaculture, Faclulty of Agriculture, Kochi University, Nankoku, Kochi 783-8502, 3Kochi Prefectural Sukumo Fisheries Guidance Office, Sukumo, Kochi 788-0265, 4Kochi Prefectual Fisheries Experimental Station, Susaki, Kochi 785-0167, Japan
Temperature adaptability was compared among three different races of ayu Plecoglossus altivelis at 205-220 days of age by recording changes in their tolerance temperatures after acclimation to various temperatures. These races were raised under the same conditions from hatching up to the performance of temperature-tolerance tests to make environment factors uniform. Tolerance temperatures of the fish changed depending on the acclimation temperature within the race and there were significant differences in the indices of temperature tolerance among the races. Average critical thermal maximum and minimum acclimated to 15-23°C and ranged from 29.7-32.2°C, 2.5-6.0°C in amphidromous form, 28.7-31.7°C, 2.3-5.3°C in landlocked form and 29.7-33.0°C, 1.7-5.0°C in Setogawa artificial landlocked form. The magnitude of thermal tolerance zones for each race calculated from the upper and lower incipient lethal temperatures against acclimation temperatures were 481°C2, 415°C2 and 517°C2 respectively. These results suggested that a difference may exist in the temperature adaptability among the ayu races.