Production of External Fluorescent Marks on Golden Perch Fingerlings through Osmotic Induction Marking with Alizarin Red S

Osmotic induction marking trials with alizarin red S (ARS) were conducted on golden perch Macquaria ambigua to evaluate the use of ARS as a lower‐cost alternative to osmotic induction marking with calcein for producing external fluorescent marks on hatchery‐produced fish. After a 10‐min immersion in a 5% solution of salt, experimental groups of golden perch were rinsed for 5 s in freshwater and immersed for 10 min in either a 0.1% or 0.5% solution of ARS, whereas control groups were either left untreated or immersed in a 0.1% solution of ARS for 10 min without prior immersion in the salt solution. All fish treated in the 0.5% solution of ARS died within 5 min of immersion, but no mortalities were observed in any of the controls or fish treated with the 0.1% solution of ARS. External fluorescent marks were observed on both the osmotic induction‐marked fish and the direct ARS immersion‐marked fish 100 d after treatment, but the osmotic induction‐marked fish possessed more intense marks. Clear marks remained visible on fish marked by osmotic induction 9 months after treatment. This study indicates that highly visible external marks can be produced through osmotic induction with ARS at a substantially lower cost than marks produced through osmotic induction with calcein. Although further refinement and testing are needed, we conclude that the method has considerable potential for use in the mass marking of fish.