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Why do many egg-laying fishes produce thousands or millions of eggs?

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A porcupine fish in the Andaman Sea — fish *Diodon hystrix* is a species of porcupine fish. These fishes are short and broad-bodied, with large eyes and spines covering their skin. Like puffer fishes, they inflate their bodies when threatened.

Many egg-laying fishes produce thousands or millions of eggs primarily as a strategy to ensure the survival of their species in the face of extremely high mortality rates.12

Because most of these species practice external fertilization and do not provide parental care, their eggs and larvae are highly vulnerable to environmental factors—such as wave action and temperature changes—and predation by other animals. In many cases, mortality for these early life stages exceeds 99 percent. By producing a vast quantity of eggs, these fishes increase the statistical probability that at least a small number of offspring will survive to reach reproductive maturity.3412

This high fecundity represents an evolutionary balance; while individual eggs contain fewer provisions for development compared to species that lay fewer eggs, the sheer volume of offspring compensates for the significant losses experienced in the wild.1