Otolith-marking experiments of juvenile black rockfish Sebastes schlegeli using alizarin complexone

Effective conditions for alizarin complexone (ALC) staining of otoliths were examined in black rockfish to establish the optimum ALC marking methods. Juvenile black rockfish (45 mm TL) were immersed in three immersion concentrations (15, 30 and 50 mg/l) of ALC for three treatment durations (6, 12, 24 h). The survival rate, ALC mark visibility and duration of the mark were investigated over two years. The survival rates 10 days after ALC immersion for 15 mg/l treatment were 99.9% in two water tanks, showing significantly higher values than the 52.4% and 81.7% for 30 mg/l, and 13.7% and 3.9% for 50 mg/l. In addition, the 15 mg/l treatment showed the highest value in visibility of ALC marks on otoliths. The ALC marks were visible for over two years without polishing the otolith. Costs of ALC marking per fish under the conditions of 15, 30 and 50 mg/l were 1.50, 4.47 and 57.0 yen, respectively. Among the concentrations used in this experiment, 15 mg/l was concluded to be the optimum concentration of ALC for otolith marking of black rockfish.