CYTO-HISTOLOGICAL EXAMINATION OF POST-VITELLOGENESIS AND FINAL OOCYTEMATURATION IN CAPTIVE-REARED STRIPED BASS

The ovarian development of captive-reared, striped bass, Morone saxati lis was examined during a 10-week period encompassing the spawning sea son. Vitellogenic oocytes in March had a mean diameter of 838 +/- 18 m u m and did not grow significantly thereafter. Except from one non-hor mone-treated fish, all females failed to undergo final oocyte maturati on (FOM) and their ovaries became atretic with the onset of high sprin g temperatures. A clearing fixative was found useful identifying early stages of atresia, evident by the absence of the germinal vesicle (GV ). Final oocyte maturation of fish treated with gonadotropin-releasing hormone agonist (GnRHa) consisted of two phases. Early FOM lasted fro m 1 to 3 weeks, and was associated with lipid-droplet coalescence, and displacement of the GV and yolk globules to the peripheral cytoplasm. Late FOM lasted <24 h, and consisted of yolk-globule coalescence and GV breakdown (GVBD). Ovulated eggs had completely coalesced lipid and yolk masses. with cortical alveoli lined against the cell wall. Both p hases of FOM were associated with significant increases in oocyte diam eter. Striped bass oocytes showed important morphological differences compared to oocytes of other members of the Moronidae Family. in terms of percentage lipid content, chorion thickness and degree of hydratio n after ovulation. (C) 1997 The Fisheries Society of the British Isles