OOCYTE MATURATION TRIGGERED BY THE PRESENCE OF MALE IN THE BLUE GOURAMI, TRICHOGASTER-TRICHOPTERUS

Oocyte growth in females of Trichogaster trichopterus kept in solitary confinement or in groups of up to 20 specimens is arrested at the end of the vitellogenetic stage. In approximately 60% of the pairs tested , a large number of oocytes mature during the first 2 days after pairi ng a female with a male. Mature oocytes contain a large apical lipid i nclusion formed by coalescence of lipid droplets that were formed duri ng the cortical alveolar stage. During maturation, the nucleus migrate s toward the oocyte periphery. Five successive steps of the migration process have been recorded. After the arrival of the nucleus at the oo cyte periphery, the nuclear membrane disintegrates and fragments of it appear in the cytoplasm surrounding the nucleus. At the same time, th e vitelline membrane opposite the nucleus invaginates into the ooplasm . Within the invagination, a large follicular cell, i.e., the micropyl ar cell, appears, sending thin cytoplasmic processes into the zona rad iata, thus forming the micropyle. These related maturation processes, i.e., formation of the apical vesicle, nuclear migration, disintegrati on of the nucleolemma, invagination of the vitelline membrane, appeara nce of the micropylar cell, and the formation of the micropyle, requir e the presence of a mature male in the same container with the female. (C) 1994 Wiley-Liss, Inc.