Validation of daily increment formation in otoliths for three Diplodus species in the Mediterranean sea

The efficacy of two fluorochromes, chlorhydrate of tetracycline (CHTC) and alizarin complexone (ALC), to induce a label on the otoliths of juvenile sparid fishes by immersion techniques was tested in different experimental conditions. CHTC did not mark otoliths in natural sea water and was toxic in divalent cation-free sea water. Immersing fish in a 50-mg 1⁻¹ ALC natural seawater solution for 24 h induced a well-defined mark on the otoliths and had no effect on survival. A daily periodicity of increment formation on otoliths was observed in captivity for Diplodus vulgaris and D. puntazzo , and was conserved in natural environment for D. sargus . The frequency of increment deposition did not vary with the age of juvenile fishes. Thus, otolith microstructure analysis will be a reliable method to give age estimates in these three sparid species during their juvenile life.