Experimental evaluation of calcein and alizarin red S for immersion marking grass carp Ctenopharyngodon idellus

Calcein (CAL) and alizarin red S (ARS) at concentrations of 50-200 and 150-300 mg/l, respectively, were used for immersion marking juvenile grass carp Ctenopharyngodon idellus. With the exception of non-lateral line scales from the 150 mg/l ARS treatment and lateral line scales from the 150, 200 mg/l ARS treatments, immersion for 24 h produced detectable marks in sagittae, lateral line and non-lateral line scales, and fin rays (dorsal, pectoral, ventral, anal, and caudal) at 100 days post-marking. Detectable fluorescent marks in sagittae were readily observed at concentrations of 150-200 mg/l CAL or 200-300 mg/l ARS. Marks were poorly visible in all non-lateral line and lateral line scales from ARS-treated groups. Fluorescent marks were readily detected in non-lateral line and lateral line scales at 150-200 mg/l CAL, and in fin rays at 100-200 mg/l CAL or 150-300 mg/l ARS. In particular, optimal marks were observed at comparatively high concentrations investigated in sagittae (300 mg/l ARS) and fin rays (100-200 mg/l CAL or 250-300 mg/l ARS). There was no significant difference on the survival or growth of marked fish compared to controls throughout the experiment (P > 0.05).