Validation of age estimates in sparid fish using flubrochrome marking

Abstract

The marking of sparid otoliths by means of oxytetracycline and alizarin complexone was investigated by immersion, feeding and intraperitoneal and intramuscular injections. Of these techniques, immersion for 24 h in a 100–150 mg·ℓ⁻¹ seawater solution of alizarin complexone was found to be most suitable for marking larval and small juvenile fish. Intramuscular injections of oxytetracycline at a dosage of 250 mg·kg fish⁻¹ was the most suitable method for marking the otoliths of juveniles in the laboratory, while dosages between 50 and 100 mg·kg fish⁻¹ were used to mark adults in the field. Feeding labelled food to the fish and intraperitoneal injections did not produce a clear mark in the otolith. Fluorochrome marks confirmed the daily periodicity of micro-increment formation in some captive sparid species (Diplodus sargus and D. cervinus), and field experiments using Chrysoblephus laticeps showed that this method was a relatively simple way of directly validating age estimates in sparid fish.