Optimization of key procedures for fish tagging and releasing with its application to yellowfin seabream (Acanthopagrus latus)

Tagging and releasing techniques are commonly used to obtain information on behavior and assess the effects of stock enhancement in marine fishes, which is based on the sampling of tagged population. However, the lack of the field protocol on fish tagging techniques undoubtedly leads to the tag loss or even the death of a large quantity of tagged fish. In this study, Acanthopagrus latus, one of the main stocking species in northern South China Sea, was employed to conducted the 40 days experiment using T-bar anchor tags. Three factors in the key tagging procedures were considered: (a) anesthetized or not (anesthetized or unanesthetized); (b) tagging locations (anterior dorsal muscle or posterior dorsal muscle) and (c) implanted angles (45° or 90°). According to a 2×2×2 factorial design, the experiment was divided into 8 tagged groups and 1 control group, with 3 replicates per group and 30 juvenile A. latus initial average body length (10.05±0.39) cm per replicate. Rates of growth, survival and tag retention were evaluated quantitatively by multifactor analysis of variance. The results showed that there was no significant difference in the specific growth rate among groups. Anesthetized or not was the factor that produced very significant difference in survival rate. Tagging locations and implanted angles produced significant difference in tag retention rate. Tagging by T with 45° into the anterior dorsal muscle of A. latus was the optimal procedures, which had the highest survival rate of 95.56% with tag retention rate of 98.89%. Finally, the field protocol suggestion was proposed: ① the fish should be reared no less than 3 days before being tagged; ② the tagging equipment should be sterilized using 75% alcohol for 5 minutes; ③ the fish should be anesthetized using 30 mg/L eugenol solution or MS-222 until they could not maintain equilibrium; ④ the fish should be tagged with angles of 45° into the anterior dorsal muscle; ⑤ the fish should be sterilized using 5% povidone iodine or KMnO₄ for 30 minutes; ⑥ the tagged fish should be then reared for 7 days before being released. This study will provide basic data for fish tagging studies in the future.