↵1-a Fish (Stenotomus chrysops) were treated with 0.1 or 5 mg/kg TCB and sampled as described inMaterials and Methods. Four or five gallbladders were pooled from each treatment group for analysis of bile residues. Concentrations are given in ng of TCB or TCB metabolites/g of gallbladder. All parent TCB and metabolite concentrations are based on the GC/ECD quantification, after confirmation by GC/MS. Although the MSD was run in the selected ion monitoring mode, a sufficient number of ions were monitored to distinguish these four metabolites from most interferences. The fragmentation pattern could not be used at concentrations below ∼5 ng/g gallbladder. In those cases, only the retention time was used to identify the metabolite. TCB and TCB metabolites were not detected in the bile of corn oil-treated fish or untreated fish (limit of detection: 0.5 ng/g gallbladder). Analytes were identified as their methylated (MeO) derivatives, but are referred to as the unmethylated hydroxylated structures.