VALIDATION OF DAILY INCREMENT FORMATION IN OTOLITHS FOR 3 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 j uvenile sparid fishes by immersion techniques was tested in different experimental conditions. CHTC did not mark otoliths in natural sea wat er and was toxic in divalent cation-free sea water. Immersing fish in a 50-mg l(-1) ALC natural seawater solution for 24 h induced a well-de fined mark on the otoliths and had no effect on survival. A daily peri odicity of increment formation on otoliths was observed in captivity f or Diplodus vulgaris and D. puntazzo, and was conserved in natural env ironment for D. sargus. The frequency of increment deposition did not vary with the age of juvenile fishes. Thus, otolith microstructure ana lysis will be a reliable method to give age estimates in these three s parid species during their juvenile life. (C) 1997 The Fisheries Socie ty of the British Isles.