External fertilization
External fertilization is the union of sperm and egg outside the parents’ bodies, usually after eggs and sperm are released into the environment.
Gamete: A reproductive cell, such as a sperm or egg, that carries one set of chromosomes. Sperm and eggs are the cells released to unite during external fertilization.
Broadcast spawning: A reproductive strategy in which aquatic animals release eggs and sperm freely into the water. It is a widespread form of external fertilization among marine invertebrates.
Internal fertilization: Fertilization in which sperm and egg unite inside a parent’s body. It contrasts with external fertilization in the location of gamete union and the conditions surrounding it.
Fecundity: The reproductive capacity of an organism, often measured by the number of eggs produced. Producing many gametes can offset the low chance that any particular pair will meet.
Fertilization: The union of sperm and egg that produces a zygote. External fertilization is one way fertilization occurs, distinguished by where the union takes place.
Frog reproduction: The reproductive cycle of frogs, commonly involving eggs and sperm released into water. Many frogs fertilize eggs externally during amplexus, when a male clasps a female.
Oviparity: Reproduction in which animals lay eggs that develop outside the parent’s body. Egg-laying can follow either external or internal fertilization, separating egg location from fertilization location.
Sperm competition: Competition among sperm from different males to fertilize an egg. When eggs and sperm are released together, sperm from multiple males may compete for fertilization.
Spawning: The release of eggs and sperm into water by aquatic animals for reproduction. Many externally fertilizing animals coordinate gamete release through spawning.
Salmon reproduction: The spawning behavior and life cycle of salmon, which lay eggs in freshwater gravel nests. Salmon release eggs and sperm over a nest, where fertilization occurs externally.