How de we know that the tags don hurt the fish?
Since fish can’t talk, the best way to answer this to observe their behavior in comparison to fish that are not carrying transmitters. Stressed fish do not eat, swim, grow, school, or engage in normal dominance behavior the same as unstressed fish, so negative affects can be observed. These types of tags have been used since the 1980’s on many species, so this question has been addressed often by watching fish in large aquariums with tags, without tags, and with “dummy” tags that look like transmitters but don’t transmit. Tagging follows strict guidelines and the fish are anesthetized during tag insertion. Tags are covered with inert nontoxic resin. After an initial adjustment period less than two days, tagged fish act and interact just like untagged fish. Growth can be slower in small fish because they may eat less, but we only tag fish well above the size guidelines.
