These Animals Spawn the Most Offspring in One Go

Spawning fish release lots of eggs—but one species is egg-ceptional.

With 2,000 babies to bear, seahorses seem to find it expedient to give birth like living confetti cannons.

Male seahorses are the ones who give birth. Females insert their eggs into a male’s brood pouch, as few as 150 or as many as 2,000, depending on the species.

It made Weird Animal Question of the Week wonder: “What are some animals that give birth to huge numbers of offspring at once?” 

WATCH A SEAHORSE GIVE BIRTH TO 2,000 BABIES Male seahorses possess the remarkable ability to give birth to thousands of babies at once.

A Lotta Mola

The mola, or ocean sunfish, looks like an animal cracker someone bit in half. At 5,000 pounds, though, this temperate and tropical water animal is the world’s heaviest bony fish.

It’s also the heavyweight egg producer, releasing 300 million eggs over a spawning season. 

So how do you count 300 million eggs free-floating in the ocean?

You don’t.

Marine biologists would likely have “counted a small number of eggs,” from a female mola ready to ovulate, says Kathleen Cole, a marine biologist at the University of Hawaii at Manoa.

Bluefin tuna can produce 10 million eggs per year.
PHOTOGRAPH BY PAUL SUTHERLAND, NATIONAL GEOGRAPHIC CREATIVE

Scientists weigh a specific number of eggs, then repeat the process to get an accurate average, then weigh all the eggs to get a total estimate, Cole says.

Selina Heppell, head of the Department of Fisheries and Wildlife at Oregon State University, says other fish known to have high numbers of eggs include sturgeon (up to 2.5 million eggs for Atlantic sturgeon) and large tuna (bluefin tuna can produce 10 million eggs a year).

A captive-bred Atlantic sturgeon (Acipenser oxyrhynchus) photographed in Berlin, Germany.
PHOTOGRAPH BY SOLVIN ZANKL, NATURE PICTURE LIBRARY

“The largest fish with the most eggs also tend to be older, experienced females that have high fertility rates,” Heppell says. (Can we hear it for older, experienced females?)

As the females grow, their larger ovaries can hold more eggs “so if the fish doubles in length,” the number of eggs will “multiply by 30 or 60,” Coleman says. It’s understood among those who fish not to take large females, “because in some species the largest females are equivalent 30 or even 60 small females.”

And those eggs are often more likely to hatch, Heppell says.

Many eggs of spawning fish don’t make it.

The tiny mola eggs “have very, very small chances of survival,” Heppell says. “Even species with lots of eggs can be overfished or reduced by climate change.”

In a stable population, Heppell says, each adult replaces itself, so those 300 million eggs should produce two adult mola. Yet, the mola is still listed as vulnerable by the International Union for the Conservation of Nature, partly due to accidental capture by fisheries targeting other species.

The African driver ant can produce 3 to 4 million eggs every 25 days.
PHOTOGRAPH BY GILBERT M. GROVESNOR

Baby, Baby

Rabbits are exceptional lifetime breeders and their litter size is an average of 14 kits. The tailless tenrec of Madagascar has litters of up to 32, according to the IUCN, while the naked mole rat has an average of 28.

A tailess tenrec (Tenrec ecaudatus) in Madagascar.
PHOTOGRAPH BY JOEL SARTORE, NATIONAL GEOGRAPHIC PHOTO ARK

Insects are no slouches when it comes to reproduction and the African driver ant, which can produce 3 to 4 million eggs every 25 days, is thought to be the most generous of all.

Finally, North America’s grey partridge lays one of the largest clutches of eggs among birds, up to 22 eggs, with an average of 16 to 18.

So, if you had a bus, it could hold a partridge family.

The grey partridge lays one of the largest clutches of eggs among birds—up to 22 at a time.
PHOTOGRAPH BY DO VAN DIJCK, FOTO NATURA, MINDEN PICTURES, NATIONAL GEOGRAPHIC CREATIVE

Header Image: The mola can release 300 million eggs over the course of one spawning season. PHOTOGRAPH BY HIROYA MINAKUCHI, MINDEN PICTURES, NATIONAL GEOGRAPHIC CREATIVE

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