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The African annual fish can reach sexual maturity in about two weeks, scientists found, the fastest known among vertebrates.

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An adult male killifish, which goes from egg to sexually mature adult in just two weeks, can also have a flexible lifespan, researchers found.CreditR. Blažek

Killifish are a family of freshwater fish that have evolved to survive in the most difficult of situations. Here in the United States, for instance, the Atlantic killifish is known for having adapted to live in heavily polluted places like the Lower Passaic River.

But in small murky puddles that come after heavy rains in parts of East Africa, another killifish, called Nothobranchius furzeri, or the African annual fish, has developed its own unique adaptations to its environment. Its embryos are able to enter a state of diapause, similar to hibernation in bears, when conditions aren’t right.

It turns out that entering dormancy isn’t the only thing that’s unusual about this African killifish. In a paper published on Monday in Current Biology, a team of Czech researchers report that N. furzeri has the quickest known rate of sexual maturity of any vertebrate — approximately two weeks. By studying the fish’s unusual life cycle, they hope to gain insights into the process of aging in other vertebrates, including us.

7-day-old killifish observed in Mozambique.CreditM. Vrtílek, J. Žák, M. Reichard

Dr. Martin Reichard, a biologist who is studying the evolution of aging at the Czech Academy of Sciences’ Institute of Vertebrate Biology, led a team of colleagues to Mozambique to study the fish’s developmental stages in the wild. There, they were able to observe embryos buried in the sand that had entered a dormant state. They also documented their maturation after rainfall.

The same killifish, 10 days later.CreditM. Vrtílek, J. Žák, M. Reichard

“The fish display comparable cellular deterioration and changes found in aging humans after several decades,” said Dr. Reichard.

With this information, the researchers found that the fish’s life cycle depends on the environment in which the embryo is laid. For example, during long periods of drought, embryos will undergo three periods of dormancy to ensure their survival.

What makes this fish’s life cycle different from other vertebrates is a trait that is commonly found in invertebrates. The embryos have a protective shell, shielding them from severe conditions.

A pool with kilifish. For most of the year, the tiny fish live as embryos buried in sediments across the African savannah, hatching when rainwater fills the small pools. They then have to grow, mature and reproduce before the pool dries up.

CreditM. Reichard

“Usually, vertebrates cope with harsh conditions during their adult stage, like bears during wintertime. However, with the embryos, it can be observed during their early developmental stages,” said Dr. Reichard.

For now, the research could contribute to the study of aging. Can understanding this species’ adaptations to its environment benefit humans by helping identify specific genetic codes unique to longevity? Or can it help pharmaceutical developers understand how drugs affect different age groups? The answer remains undiscovered.

Correction: 

An earlier version of this article incorrectly compared a fish embryo’s protective shell. It is like a layer found around the eggs of some invertebrates, not like a shield around a plant’s seed.

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