Annual killifish (Nothobranchius furzeri) have a live-fast-die-young type of lifestyle. The fish embryos survive in a dried inactive state in sediment. When it rains, they are activated, somewhat like plant seeds. Therefore they need to hatch, mature, and produce offspring on a ticking clock before the pools dry up. Scientists have found that this lifestyle has caused the killifish to become the fastest maturing vertebrate.

Previously, only laboratory studies have examined the lifestyle of the killifish and it turns out that they have underestimated their lifespan. In the lab, the fish live on average three to four weeks, though it can take up to ten weeks. It can be rather variable and the researchers suspected that the fish might mature even quicker in natural populations.

An annual killifish. Image credits Leibniz Institute for Age Research – Fritz Lipmann Institute (FLI), Jena, Germany,

“We guessed that some populations of this species could achieve very rapid growth and sexual maturation under particular conditions,” says Martin Reichard of the Institute of Vertebrate Biology, The Czech Academy of Sciences. “But we have found that this rapid maturation is the norm rather than a rare exception.”

How the fish and their habitat look like after 1, 2, and 3 weeks. Image credits: M. Vrtílek, Ják, M. Reichard.

The research team surveyed killifish in the wild across southern Mozambique. Fish were collected from eight pools within three weeks after the pools filled with rainwater. By comparing the age of the fish with the time of pool filling, it was determined that the fish hatched from their eggs after three days of being immersed in water. By analyzing the fish’s gonads, the researchers found that they were sexual mature after a mere 14 or 15 days.

So, these fish hatch at under a millimeter in size and grow to full size, four or five centimeters, and start reproducing after only two weeks! They receive the prize for the youngest vertebrate parents.

Journal reference: Vrtílek et al. 2018. Extremely rapid maturation of a wild African annual fish. Current Biology.

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