Abstract: In the identification of fish, tags having on at least one side visually detectable markings encoding information pertaining to a fish are shallowly implanted within transparent or semi-transparent tissues of respective specimens. Upon release and subsequent capture of the fish specimens, the locations of the tags are optically determined by a visual inspection of the fish. The information is retrieved from the tags by either reading the information from the implanted tags through the transparent or semi-transparent tissue or excising the tags and thereupon reading the information. In either case, the specimens are not significantly harmed or injured by virtue of the implantation and reading operations. The implanted tags also have a minimum effect on survival and other biological traits and behavior.