Study on otolith marking of larval common carp Cyprinus carpio by immersion in alizarin complexone

The artificial release is one of successful approaches for natural fishery stock enhancement. Therefore, effective marking techniques are expected to be applied for assessment of the contribution of released fishes to the fishery resources. Because fish at larval stages are better for batch marking and releasing, in the present study, larval common carp Cyprinus carpio were immersed in the 100 mg/L of alizarin complexone (ALC) for 48 h, so as to compare and investigate the marking characteristics of this method among sagitta, asteriscus and lapillus, as well as the possible time lag between start/end of fish ALC immersion and corresponding start/end of the fluorescent signal on otolith. Results suggested that marking rings in aforementioned three types of otolith were significantly observed in both visible and fluorescent lights. As for the ALC marking effect, asteriscus (the best) and lapillus (the second) were relatively better than sagitta. One-day time lag was found, respectively, between start of fish immersion and corresponding start of otolith marking, as well as end of fish immersion and corresponding end of ALC marking in extended area on otolith. The otolith ALC marking rings could still be obviously noted, even the fish was reared for 50 days after end of immersion. This phenomenon showed that ALC marking ring could be preserved on otolith for quite a long period. Consequently, the present method of ALC immersion will have strong feasibility for otolith ecological marking of larval C. carpio.