The assumption that marking does not alter the vulnerability of fish to a visual predator was examined. Similar numbers of age-0 steelheadOncorhynchus mykisswere tagged with binary-coded-wires, tagged with passive integrated transponders, freeze branded, marked with fingerling tags, or left unmarked. All were subjected to age-1 steelhead predators for 24 h in 2.4-m-diameter circular tanks filled with clear well water. Twice as many marked as unmarked age-0 steelhead prey were eaten. There was no significant survival difference among the four marked treatment groups, which suggested that in the laboratory the trauma associated with marking is more important than mark type. We conclude that marking may effect postrelease survival and recommend that mark–recapture experiments be used to empirically determine and correct for differences in survival of marked and unmarked fish.