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Why do many fish lay very large numbers of eggs?

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Illustration showing examples of vertebrates: a turtle for reptiles, a songbird for birds, a bluegill fish, a salamander for amphibians, and two mammals-a whale and a groundhog. — Vertebrate The major groups of vertebrates include fishes, amphibians, reptiles, birds, and mammals.

Many fish species produce a large number of eggs primarily as a strategy to offset extremely high rates of mortality among their eggs and larvae.123

Because most bony fishes utilize external fertilization, their eggs are often scattered in open water or on the substrate without the protection of the parent's body. This leaves the offspring highly vulnerable to environmental factors and predators. By releasing hundreds, thousands, or even millions of eggs, these species increase the statistical probability that at least a few individuals will survive to reach maturity.123

This reproductive approach represents an evolutionary balance: species that do not provide parental care typically produce many small eggs with limited nutritional provisions, whereas species that invest in internal development or parental protection produce fewer, better-provisioned offspring. Ultimately, high fecundity is a necessary adaptation for species facing significant risks in their early life stages.123