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"Annual Fish" Grow Up at Top Speed

Certain African fish evolved short generations to survive in temporary ponds that dry up after just a few months each year. Sophie Bushwick reports

In the east African savanna, pools of water form during the rainy season only to dry up a few months later. Being a fish in one of these temporary ponds is a challenge. To survive, they race to maturity, with the shortest generation time of any vertebrate.

To monitor the development of the so-called annual fish, researchers raised two different species in the lab.

The fish could grow by almost a quarter of their body length each day. One species could already reproduce at 17 days of age. The other took an additional day. The eggs these youngsters fertilized then hatched in as little as 15 days, leaving only a month between generations. The study is in the journal EvoDevo. [Radim Blažek, Matej Polačik and Martin Reichard, Rapid growth, early maturation and short generation time in African annual fishes]

Embryonic annual fish survive the dry season by lying dormant underground. Once the rains return and the pool forms, they quickly reproduce before the water dries up again. Their short generation time is thus a crucial evolutionary adaptation. Their temporary ponds force them to live fast, die young and leave a desiccated corpse.

—Sophie Bushwick

[The above text is a transcript of this podcast.]

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