FORMATION OF INITIAL DAILY INCREMENTS IN SAGITTAL OTOLITHS OF REARED AND WILD SARDINA-PILCHARDUS YOLK-SAC LARVAE

Daily deposition of growth increments in sagittal otoliths of reared and wild Sardina pilchardus (Walbaum 1792) larvae from hatching to complete yolk-sac absorption is reported. Increments laid down prior to hatching were observed. A distinct growth increment, similar or equal to 1 mu m wide and located 5 to 7 mu m from the focus is laid down on the day of hatching. Subsequently, narrower increments (< 1 mu m) are laid down daily throughout the yolk-sac stage. Measurements were made on the maximum radius of the sagittal otoliths of two groups of larvae: 83 larvae reared from fertilized eggs sampled from Ria de Muros (NW Spain), and 239 wild individuals sampled along the northern coasts of the Iberian peninsula. Counting of daily ring increments can provide a direct and valid estimation of larval age without the necessity for later correction.