Which fish lays the most eggs?

The ocean sunfish lays the most eggs of any known vertebrate. A single female can release up to 300 million eggs in one spawning event, an extraordinary number even among fish.

That huge reproductive output reflects the sunfish's difficult early life. Eggs and larvae are tiny and vulnerable to predators, currents, and starvation, while only a very small fraction survive to adulthood. Adults compensate for this high mortality by producing an enormous number of offspring.

Ocean sunfish, or mola, are the world's heaviest bony fish when fully grown, but their young look radically different. Larvae begin with rounded bodies and prominent spines before developing the familiar flattened adult form. The species' mating behavior remains poorly understood, although spawning areas have been proposed in several major oceans.

A common mix-up is confusing “most eggs” with “largest eggs” or “most offspring surviving.” The sunfish wins the first comparison; its record concerns the number of eggs produced, not reproductive success.