The Eggs of a Goldfish Are Not Producing Eggs

Mysterious breeding habits of aquarium fish vex experts


A recent scientific paper offered an explanation for the mysterious breeding habits of aquarium fish.

A team of researchers from the National Institute of Aging in Bethesda, Maryland, set out to solve the mystery of a phenomenon known as viviparity in fish – the formation of embryos that are born from eggs, which are produced by the female.

But when they looked to see what would happen to the fish that produced eggs without males, they found that their descendants were also unproductive. Some female fish kept in the lab bred as much as 50% more than expected.

“They were producing babies that were more or less as big as they were after males,” said the senior author of the study, Michael Tamanaha, Ph.D., a professor of environmental studies and biology at the University of Florida.

It all happened because the eggs of a species of goldfish known as Carassius auratus failed to hatch into developing embryos after they were deposited into the male’s genitalia.

However, the researchers found that if they removed males and transferred female goldfish to the fish’s original environment, then laid eggs into their reproductive organs, and fertilized them in the lab, then the eggs in the female’s reproductive organs were successfully fertilized – but their embryos were born into a pool of unproductive female fish.

These results provided the first evidence of viviparity in fish and an explanation for the phenomenon.

The research will be published in the Proceedings of the National Academy of Sciences on Friday.

“We were very surprised and very pleased,” said Tamanaha. “In the world of aquarium fish, it is well understood that male fish have to be present for the fertilization of their eggs. And for females in the wild, they’re constantly spawning to provide eggs for their offspring.”

In captivity, the researchers found that when they removed males, female goldfish that produced eggs were producing larger offspring than they would have done otherwise. And when female fish received eggs transferred into their reproductive organs in the laboratory and fertilized them in the lab, the embryos produced in their organs were successfully grown in

Leave a Comment