Examples of external fertilization can be seen in frogs, some marine invertebrates, and many types of fish. External fertilization occurs when sperm fertilize eggs outside of the female animal’s body. Often, in order for a viable number of eggs to be fertilized, the female needs to lay a large number of them. For example, Chinook salmon can lay up to 14,000 eggs in a nest.
Most frogs need to lay their eggs in a body of fresh water. Male frogs call from the edge of a pond or stream and attract females. During external fertilization, the male grabs the female in what is called the amplexus and they enter the water. She then releases her eggs at the same time that he releases sperm. The fertilized eggs hatch into tadpoles.
Many species of salmon return to their home streams to breed. The female digs a nest, or redd, in the stream bed and lays eggs in it. The male then swims over the nest and fertilizes the eggs.
Coral animals don’t even need to participate in courtship or strenuous migration to reproduce. Most stony corals simply release eggs and sperm into the water. When these gametes meet, they create an embryo.
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