Size can't be used to determine the age of fish, because different water temperature, water quality, feeding frequency and amount will affect the individual size of fish. When there is a public female, it will naturally mate at maturity. After the female fish carries the fetus, the belly will gradually become bigger and rounder, and the fetal spot will gradually increase. When it is about to give birth, the stagnation hole will slightly protrude into a small tip. Moonlight is also a kind of viviparous fish. Eggs are fertilized in the mother fish to develop into small fish, which are then produced by the mother fish.