Fish and amphibians commonly conduct fertilization externally. External fertilization occurs when the female releases the eggs into the environment and then the male releases sperm on top of the eggs.The eggs are then fertilized. Internal fertilization occurs when fertilization happens inside the female's body. After fertilization, the female either bears live young or lays eggs which hatch. Both of these processes take place after a period of incubation either internally or externally. Eggs which are externally fertilized do not have a hard external protective covering or shell.