1. The purpose of this study was to compare tributyltin (TBT)-induced cytochrome P450 1 (CYP450 1) regulation in liver, gills and muscle of juvenile common carp (Cyprinus carpio). 2. Fish were exposed to sublethal concentrations of TBT (75, 0.75 and 7.5 μg/L) for 60 days. CYP450 1A was measured at the enzyme activity level as 7-ethoxyresorufin-O-deethylase (EROD) activity, as well as the mRNA expression of CYP450 1 family genes (CYP1A, CYP1B, CYP1C1 and CYP1C2) in fish tissues. 3. Based on the results, the liver displayed the highest absolute levels of EROD activity, both under nonexposed and exposed conditions. Additional, EROD activities and CYP1A gene levels showed a good correlation in all three organs. According to the mRNA expression of CYP450 1 family genes, it suggested that CYP1A was to accommodate most EROD activity in fish, but other CYP450 forms also involved in this proceeding. 4. Overall, the study revealed both similarities and differences in the concentration-dependent CYP450 1 responses of the three target organs, which could provide useful information to better understand the mechanisms of TBT-induced bio-toxicity.

b University of South Bohemia in Ceske Budejovice Faculty of Fisheries and Protection of Waters South Bohemian Research Center of Aquaculture and Biodiversity of Hydrocenoses Vodňany Czech Republic

c College of Fisheries Huazhong Agricultural University Wuhan Hubei China and

Key Laboratory of Aquatic Science of Chongqing School of Life Science Southwest University Chongqing China

Observation Station for Fishery Resource and Environment in Upper Middle Reaches of Yangtze River Yangtze River Fisheries Research Institute Chinese Academy of Fishery Sciences Wuhan China

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