The cognitive abilities of animals are challenging to assess. Typically, studies on visual discrimination in fishes are conducted in the laboratory neglecting the fact that acclimation of test subjects to the laboratory environment including artificial light conditions may affect the way in which fishes respond to visual stimuli. The aim of this study was to demonstrate that it is possible to train fishes on visual cues using food rewards, while free-roaming in their own territory under natural conditions. An acoustic secondary reinforcer was also included and its potential contribution to the training success was tested. We trained 27 specimens of the benthic triplefin blenny Tripterygion tripteronotum on either a black or white colored target. Training took on average ten days. In 15 binary choice trials, 23 fish discriminated successfully between rewarded target cue (CS ) and the unrewarded cue (CS−). Furthermore, we discuss the usefulness of acoustic secondary reinforcement in this study.