Otolith tagging of ayu embryo with fluorescent substances.

In order to expand the possibility of otolith tagging for mass-marking of fish larvae and embryos, the eggs of ayu Plecoglossus altivelis, an amphidromous salmonoidei fish, were immersed in the solutions of three different fluorescent substances. Alizarin complexone (ALC) presented a distinct scarlet-pink fluorescent ring in the embryonic otolith under UV light, whose optimum condition for treatment was 50-200mg/l for about 1 day. Clear yellow marks were also obtained by tetracycline (TC) treatment at 200-300mg/l for 1 day. Comparing with these two chemicals, calcein (CAL) showed a less distinct yellowish green fluore-scence at about 500mg/l for 1 day, but without any optimum treatment conditions which satisfied both 100% marking success and near 100% survival during treatment. Double treatments by ALC (200mg/l for 1 day) at embryonic stage and by TC (300mg/l for 1 day) at newly hatched larval stage presented discernible double circular marks of an inner red fluorescent ring and an outer yellow one with a good survival (about 98%), suggesting the possi-bility of multiple treatment with different chemicals of different fluorescent colors. These results promise to increase the number of mark kinds with which different fish groups can be distinguished one another in an experiment.