African fish is fastest-maturing vertebrate

Male Nothobranchius kadleci fish Male Nothobranchius kadleci can go from eggs to fathers in one month

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Tiny fish that live in temporary puddles in Africa reach sexual maturity faster than any other animal with a backbone, say scientists.

One of the studied species of killifish - Nothobranchius kadleci - started to reproduce at the age of 17 days.

Researchers found that some eggs reached hatching stage in 15 days meaning they also have the shortest minimum generation time in vertebrates.

The results are published in the open access journal EvoDevo.

Dr Martin Reichard and colleagues from the Institute of Vertebrate Biology, Academy of Sciences of the Czech Republic studied the aging processes of two species of wild-caught fishes from southern Mozambique under laboratory conditions.

In the wild, these fishes live in extreme conditions of temporary pools that only occur during the rainy season when savannah depressions are filled with water.

"It is biologically very relevant for these fish to be able to sexually mature very fast because their habitat may dry out in three to four weeks," Dr Reichard said.

Typical habitat of the study species: a shallow savannah depression filled with water during the rainy season Savannah depressions fill with water during the rainy season

"If they mature very fast, they can produce a new generation."

The team were "really surprised" to discover it only took 17 and 18 days for the two species being studied - Nothobranchius kadleci and N. furzeri - to become sexually mature.

Previous estimates for these fishes had been in the region of four weeks but these were observations of captive-bred populations.

All four study populations also demonstrated rapid growth rates, with one group growing nearly a quarter of their total body length per day.

"I'm pretty sure if conditions are good, they would be able to sexually mature even faster in the wild," Dr Reichard told BBC Nature.

"If conditions are inferior - food is less abundant, there is a high density of fish - it would take them longer but they can still complete their lifecycle."

Explosive growth, early sexual maturation and high reproductive investment are traits typical of extremophiles - organisms inhabiting temporary and unpredictable habitats.

But being able to develop quickly is only one of the survival strategies these fish use in the changing conditions of the seasonal pools in which they live.

During the dry season, they remain in the soil as dormant eggs and embryos, waiting for the next rains which could be more than a year away, in order to hatch and then repeat the lifecycle.

"Having some embryos that develop over a year or longer means that if there is a dry year with no rain, there would still be some embryos that hatch and the population would survive," said Dr Reichard.

"It's very important to have this bet-hedging strategy."

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