Effect evaluation of alizarin complexone marking for otoliths of juvenile black carp (Mylopharyngodon piceus)

Investigation on artificial marking technology is very important supporting work for national fish mark release recapture and effectiveness tracing evaluation issues. In this study, two-month old juvenile black carps (Mylopharyngodon piceus) had been immersed in alizarin complexone (ALC) at a concentration of 100 mg·L⁻¹ for 48 h, and then transferred to normal water for 20 d. Three pairs of otoliths (i.e., sagitta, lapillus and asteriscus) were removed from the black carps by continuous sampling, observed under fluorescence microscope and photographed, so as to evaluate the characteristics of deposition and the marking effect of ALC in different otoliths. The results show that the marked areas were clearly observed in each otolith pair under visible light and different excitation light, with a 100% mark success rate. After 20 d of recovery culture in normal water without ALC, the intensity of ALC mark in otoliths of the marked fish was still very high, showing a good marking effect. Moreover, the optimum light source was blue excitation light, followed by green excitation light. The lapillus was the optimal otolith type for ALC marking and for judgment of time lag among the three pairs of otoliths, followed by asteriscus. In addition, there was a time lag of 1 day between the carps immersed in ALC solution and ALC deposition into otolith, as well as between removing immersed carps from ALC solution and disappearance of ALC mark from otolith.