1Inland-water Fisheries Experimental Station, Kanagawa Prefectural Fisheries Technology Center, Sagamihara, Kanagawa 229-1135, 2Shiga Prefectural Fisheries Experimental Station, Hikone, Shiga 522-0057, 3Toyama Prefectural Fisheries Research Institute, Namerikawa, Toyama 936-8536, 4Inland Station, National Research Institute of Aquaculture, Fisheries Research Agency, Tamaki, Mie 519-0423, Japan
We investigated the effects of water temperature and rearing density on the development of the thymus in juvenile ayu Plecoglossus altivelis altivelis from three different origins, Shiga, Toyama and Kanagawa. The thymus volume of the ayu that had been reared at high water temperature (about 20°C) was significantly smaller than that of the ayu reared at low water temperature (about 15°C). Rearing density ranging from 0.58 to 10.95 kg/m3 water at the end of the experiment did not affect the thymus development.