Use of Alizarin Complexone Immersion for Marking Otoliths of Mozambique Tilapia

We analyzed the efficacy of alizarin complexone (AC) immersion for creating visible fluorescent marks on otoliths of Mozambique tilapia (Tilapia mossambica) and compared the success of processing the otoliths as whole mounts and sections. We immersed 51 tilapia in a buffered 21 C aerated bath of 100 mg/liter AC for 15 hours, and no mortality resulted from marking procedures. Otoliths were removed on days 1, 10, 20, 30, and 60 following marking. Whole ground mounts showed visible rings only 84% of the time, many of which were faint or incomplete. Sectioning revealed visible rings 98% of the time and appeared to be the better examination technique. There was no mark loss over time, and marks on whole ground otoliths became more visible with time (day 1-20 had 60% visibility; day 30-60 had 95% visibility) which was believed to be a result of mark proximity to otolith edge. We concluded that AC could be effectively used to mark Mozambique tilapia otoliths, and suggest sectioning be used for improved mark identification for short-term studies.

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