Pathology working group review of histopathologic specimens from three laboratory studies of diclofenac in trout.

•A Pathology Working Group (PWG) panel evaluated histopathologic sections from three prior studies of diclofenac in trout.•The panel identified two findings in the gill and liver that were related to diclofenac exposure.•The panel found little evidence to support other reported effects of diclofenac in trout.•The overall NOEC was determined to be >320μg/L.•The value of the pathology peer review/PWG approach was demonstrated successfully.