From Latin ovulum testis, diminutive of ovum egg.

Ovulation is the process by which the oocytes fall out of the ovary into the female's body cavity. Like ovogenesis, it is triggered by a hormone from the pituitary gland.

During the spawning period in female fish, whose sex glands are in stage IV of maturity, under the influence of gonadotropic hormone of the pituitary gland, oogenesis is completed and ovulation occurs (eggs emerge from the follicle). Ovulation in fish is carried out only under certain environmental conditions, among which are important water temperature, hydrochemical regime, the presence or absence of water flow, the presence of males, for many fish spawning substrate. If after the onset of spawning temperatures for this species of fish at least one of these environmental factors is unsatisfactory, ovulation does not occur, oocytes are resorbed, and follicles atresia (overgrowth).

For fish, this phenomenon is of great adaptive importance, as their ovaries are released from the oocytes of the older generation and begin a new developmental cycle.