Ovarian degeneration during the female-to-male sex change in the protogynous hermaphroditic fish, Halichoeres poecilopterus

Halichoeres poecilopterus (Labridae) is a protogynous, hermaphroditic fish common in temperate waters around Japan. Although oocyte degeneration is an established event at the onset of sex change, there is little information on the process. We examined cell numbers and proportional ratios of ovarian germ cells in sex-changing gonads of H. poecilopterus. This confirmed a lack of YV (yolk vesicle stage) and Y (yolk stage) oocytes, a rapid decrease of P (perinucleolus stage) oocytes, and a slight increase of CN (before/at chromatin nucleolus stage) germ cells. We discuss gonadal conditions necessary for the protogynous sex change of H. poecilopterus.