External fertilization is characterized by the release of both sperm and eggs into an external environment; sperm will fertilize the egg outside of the organism, as seen in spawning. Internal fertilization is characterized by sperm fertilizing the egg within the female; the three methods include: oviparity (egg laid outside female body) , ovoviparity (egg held within female), and viviparity (development within female followed by live birth). Internal fertilization protects the fertilized egg or embryo from predation and harsh environments, which results in higher survival rates than can occur with external fertilization. Ovoviparity is characterized by an organism retaining a fertilized egg inside the body where development occurs and nourishment is received from the yolk. Viparity is characterized by an organism which has its young develop within the female and nourishment is received directly from the mother via a placenta.

Frst female fish lays eggs in water which is followed by releasing of sperms by male fish so many of dem r fertilized nd others are destroyed by external conditions