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 ∼ 60% of the pairs tested, a large number of oocytes mature during the first 2 days after pairing a female with a male. Mature oocytes contain a large apical lipid inclusion formed by coalescence of lipid droplets that were formed during the cortical alveolar stage. During maturation, the nucleus migrates toward the oocyte periphery. Five successive steps of the migration process have been recorded. After the arrival of the nucleus at the oocyte periphery, the nuclear membrane disintegrates and fragments of it appear in the cytoplasm surrounding the nucleus. At the same time, the vitelline membrane opposite the nucleus invaginates into the ooplasm. Within the invagination, a large follicular cell, i.e., the micropylar cell, appears, sending thin cytoplasmic processes into the zona radiata, thus forming the micropyle. These related maturation processes, i.e., formation of the apical vesicle, nuclear migration, disintegration of the nucleolemma, invagination of the vitelline membrane, appearance of the micropylar cell, and the formation of the micropyle, require the presence of a mature male in the same container with the female. © 1994 Wiley‐Liss, Inc.