Experimental evaluation of calcein and alizarin red S for immersion marking of silver carp Hypophthalmichthys molitrix (Valenciennes, 1844)

Calcein (CAL) and alizarin red S (ARS) at concentrations of 50–200 and 150–300 mg/L, respectively, were used for immersion marking of juvenile silver carp Hypophthalmichthys molitrix (79.65 ± 2.11 mm total length, mean ± SD). The marked fish were kept in separate tanks (0.012 individuals per litre, rearing temperature 18.4–25.7°C) for 360 days. Each experimental treatment group consisted of three replicates (16 individuals per replicate). Immersion for 24 h produced detectable marks in the sagittae, lateral line and non‐lateral line scales, and fin rays (dorsal, pectoral, ventral, anal, and caudal) at 360 days post‐marking. Acceptable marks in the sagittae were observed for CAL at concentrations of 150–200 mg/L and for ARS at concentrations of 200–300 mg/L. Fluorescent marks were poorly visible in all non‐lateral line scales from both the CAL‐ and ARS‐treated groups. Acceptable fluorescent marks in the lateral line scales and fin rays were detected for CAL at concentrations of 150–200 and 100–200 mg/L, respectively, and for ARS at concentrations of 200–300 and 150–300 mg/L, respectively. In particular, optimal marks were observed at the highest concentrations investigated in lateral line scales (200 mg/L CAL, 300 mg/L ARS) and fin rays (200 mg/L CAL, 200–300 mg/L ARS). There was no significant difference in the survival or growth of marked fish compared to controls throughout the experiment (P > 0.05).