Tri-n-Butylin Caused Mortality of Chinook Salmon, Oncorhynchus Tshawytscha, on Transfer to TBT-Treated Marine Net Pen

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Abstract
The median lethal concentrations (LC 50 's) of tri-n-butyltin oxide (TBTO) to juvenile chinook salmon, Oncorhynchus tshawytscha, adapted to seawater were determined in a static renewal bioassay. LC 50 's were 54, 20, and 1.5 \mu g TBTO/l after exposures for 6, 12, and 96 h, respectively. LC 50 's decreased logarithmically with time for exposures between 12 and 96 h. Average tri-n-butyltin (TBT) concentrations in liver, brain, and muscle tissues of salmon that died during the bioassay were 7.0, 3.5, and 0.52 \mu g TBT/g wet weight tissue, respectively. TBT concentrations in liver, brain, and muscle tissues of salmon that survived until day 4 of the bioassay were 4,300, 1,300, and 200 times exposure concentrations, respectively. Average TBT concentrations in liver, brain, and muscle tissues of salmon surviving transfer to a TBT treated marine net pen that killed 8.5% of the salmon transferred were 9.56, 3.44 and 1.24 \mu g TBT/g wet weight tissue, respectively. Our results indicate TBT exposure was the cause of death of chinook salmon exposed to TBT-treated marine net pens at one aquacultúre facility.