External fertilization

External fertilization is a mode of reproduction in which a male organism's sperm fertilizes a female organism's egg outside of the female's body. It is contrasted with internal fertilization. External fertilization typically occurs in aquatic environments where both eggs and sperm are released into the water. After the sperm reaches the egg, fertilization takes place. Most external fertilization happens during the process of spawning where one or several females release their eggs and the male(s) release sperm in the same area, at the same time.

Types of External Fertilization

There are two main types of external fertilization: broadcast spawning and nuptial dance.

Broadcast Spawning

Broadcast spawning is a method of external fertilization used by several animal species. During broadcast spawning, an organism releases its eggs or sperm into the water, where one or more males or females can fertilize them. The fertilized eggs then develop and hatch into larvae which develop into mature individuals.

Nuptial Dance

Nuptial dance is another method of external fertilization. This involves a complex set of behaviors that typically include a visual display by the male, followed by the release of sperm and eggs into the water.

Advantages and Disadvantages

External fertilization has both advantages and disadvantages. The main advantage is that it allows for a large number of offspring to be produced at one time. However, the offspring are often left unprotected, making them vulnerable to predators and environmental conditions.

Examples

Examples of organisms that use external fertilization include many species of fish, such as salmon and zebrafish, and amphibians, such as frogs and toads. Some invertebrates, such as sea urchins and corals, also use external fertilization.

See Also

• Internal fertilization
• Reproduction
• Aquatic animal
• Fish
• Amphibian

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