Otolith-marking Experiments of Juvenile Walleye Pollock Theragra chalcogramma Using Oxytetracycline, Alizarin Complexone, and Alizarin Red S

Abstract

Captive juvenile walleye pollock, Theragra chalcogramma, were immersed for 24 hours in different solutions of oxytetracycline (OTC), alizarin complexone (ALC), and alizarin red S (ARS) to determine which solutions can be used to mark their otoliths. Otoliths were successfully marked with a 25 ppm solution of ALC and 200 to 1000 ppm solutions of ARS, but, they were not marked with 100 to 400 ppm solutions of OTC. Otolith, scale, dorsal-fin ray, and subopercle marks were identified in captive yearlings one year after they were marked with ALC and ARS. Observations on otolith marks showed that annual ring patterns differed between captive and wild fish. Captive age-1 fish, which were reared under stable water-temperature, photoperiod and feeding conditions for one year, and had higher growth rates than wild fish, did not form an annual ring. Considering its low toxicity, good quality of marks, and relatively low cost, ARS is considered the most reliable immersion method of the three analyzed for marking juvenile walleye Pollock.