What Are Examples of External Fertilization?


Examples of external fertilization can be seen in frogs, some marine invertebrates and many types of fish. External fertilization happens when sperm fertilize eggs outside of the body of the female animal. Often, in order for a viable number of eggs to be fertilized, the female needs to lay a great number of them. For example, the Chinook salmon can deposit up to 14,000 eggs in a nest.

Most frogs need to lay their eggs in a body of fresh water. The male frogs call from the edge of a pond or stream and attracts the females. During the external fertilization, the male grasps the female in what’s called amplexus, and they enter the water. She then releases her eggs at the same time he releases sperm. The fertilized eggs hatch into tadpoles.

Many species of salmon return to their natal streams to reproduce. The female digs a nest, or a redd, in the stream bed and deposits eggs in it. The male then swims over the nest and fertilizes the eggs.

Coral animals don’t even need to engage in courtship or strenuous migration to reproduce. Most stony coral simply release eggs and sperm into the water. When these gametes meet, they create an embryo.