Effect of water temperature on the feeding activity and the resultant mercury levels in the muscle of cultured bluefin tuna Thunnus orientalis (Temminck and Schlegel) Masashi Ando 1 , Manabu Seoka 2 ,Yoshio Mukai 3 , Mok Wen Jye 1 , Shigeru Miyashita 4 & Yasuyuki Tsukamasa 1 1 Department of Fisheries, Kinki University, Nara, Japan 2 Uragami Experimental Station, Fisheries Laboratory of Kinki University,Wakayama, Japan 3 Amami Experimental Station, Fisheries Laboratory of Kinki University, Kagoshima, Japan 4 Shirahama Experimental Station, Fisheries Laboratory of Kinki University,Wakayama, Japan Correspondence: M Ando, Department of Fisheries, Kinki University, Nakamachi 3327-204, Nara 631-8505, Japan. E-mail: ando@nara. kindai.ac.jp Abstract Tuna muscle often contains high levels of mercury, and ¢sh samples with mercury concentrations ten times higher than the speci¢ed safety standards have been reported. Here, we report on the relationship be- tween water temperature and the concentration of mercury in the tail muscle tissue of cultured blue¢n tuna Thunnus orientalis. The ¢sh used in this study were cultured at Fisheries Laboratory of Kinki Uni- versity (Amami Experimental Station, Kagoshima, Japan). One hundred ¢sh weighing 26.2^89.4 kg were selected for analysis between February 2007 and Jan- uary 2008.Water temperature during rearing ranged from 21to 29 1C. The total mercury levels were mea- sured using the reduction vaporizing atomic absorp- tion method after acid digestion. Body weight increased approximately1.5 times that observed in a previous study, despite feeding activity either being the same or less than that observed previously. The average mercury concentration in white muscle was 0.353 mg kg  1 , remaining almost constant and inde- pendent of body growth. Unlike previous studies, sea- sonality was not observed in this study. Based on these ¢ndings, water temperatures within a certain range were considered to stabilize feeding activity and increase feeding e⁄ciency. Consequently, water temperature is considered to have a moderating e¡ect on seasonal £uctuations in muscle mercury concen- trations in cultured blue¢n tuna. Keywords: blue¢n tuna, mercury, tail muscle, ¢sh culture, food safety, water temperature Introduction The dangers associated with mercury pollution and poisoning have been reported extensively (Clarkson, Cox, Marsh, Myers, Al-tikriti, Amin-zaki & Dabbagh 1981; Dorea 2003; Gochfeld 2003), and although several of these studies were based on isolated incidents, mercury pollution is a pressing global issue. China is currently considered to have the most severe mercury pollution problem in the world because of the mercury that is dis- charged into the atmosphere through the combus- tion of coal (Dastoor & Larocque 2004; Streets, Hao, Wu, Jiang, Chan, Tian & Feng 2005). Mercury discharged in this way returns to the earth in the form of precipitation, polluting terrestrial and marine environments. Most of the mercury in the human diet is acquired from ¢sh (Nakagawa,Yumita & Hiromoto 1997), and the levels of mercury in tuna are considerably higher than those in most other edible ¢sh species (Shum, Freeman & Uthe 1979). Because mercury concentra- tions increase with every trophic level in the food chain, the mercury levels in tuna, an apex predator, are high (Peterson, Klawe & Sharp1973). Aquaculture Research, 2011, 42 , 516^524 doi: 10.1111/j.1365-2109.2010.02647.x 516 r 2010 Blackwell Publishing Ltd