The reproductive biology of the amberjack, Seriola dumerilii (Risso 1810).I. Oocyte development in captivity

A study of the reproductive biology of the amberjack, Seriola dumerilii, he ld in captivity was carried out, describing oogenesis as well as the differ ent stages of the ovarian cycle. Seven stages of oocyte development, as wel l as oogonia, were distinguished. Cortical alveoli were hardly detectable w ithin the oocyte, as they were small, sparse and contained few mucopolysacc harides. It is suggested that their role in the fertilization process might be less important than in other teleost species. Fish aged 3 and 4 years w ere found to be sexually immature, with ovaries containing only previtellog enic oocytes. Vitellogenesis started in December in fish aged 4 + years. La te-developing ovaries showing deposition of yolk protein granules were foun d at the end of the 5th year of life (May) in specimens measuring 80.0 +/- 3.5 cm standard length. This should be regarded as the minimum size at whic h sexual maturity is reached in S. dumerilii. Final vitellogenesis and oocy te maturation were, however, inhibited in captivity, and extensive follicul ar atresia took, place as the natural spawning season approached. It is sug gested that insufficient gonadotrophic stimulation because of confinement s tress may be the cause of failed maturation and spawning in this species un der culture conditions.