AGE AND GROWTH OF YELLOWFIN TUNA, THUNNUS ALBACARES, FROM THE WESTERNINDIAN-OCEAN, BASED ON OTOLITH MICROSTRUCTURE

Microincrements of otoliths of 151 yellowfin tuna, Thunnus albacares, caught in the western Indian Ocean by French and Mauritian purse seine rs were used to establish growth curves. On the basis of comparisons a mong several otolith preparations (transverse or oblique sections, ace tate replicas of the external face) and two methods of examination (li ght microscopy and scanning electron microscopy), we chose to observe transverse otolith sections in light microscopy to estimate age in day s. The von Bertalanffy growth curve, FL = 272.7 (1 - e(-0.176(t + 0.26 6))), where FL = fork length in cm and t in years, is very similar to those obtained by other investigators. It does not support the hypothe sis that yellowfin tuna of the eastern Atlantic Ocean and the western Indian Ocean have two growth stanzas. Back-calculated dates of spawnin g show that yellowfin tuna spawn successfully throughout the year, but principally between November and March.