This small African fish matures in just two weeks, even faster than previously suspected, giving it the shortest time from egg to mating of any vertebrate known.
While poets have celebrated the fact some insects live for just one day in their adult form, vertebrates operate at a more stately pace. The African killifish (Nothobranchius furzeri), popular as a research model, was known to be something of an exception. Its eggs can wait for years in dry lake beds, developing rapidly when the rains come so it can breed before the lake dries up.
Nevertheless, laboratory measurements of the speed with which the fish develops underestimate the fish’s growth rate, allowing it to set records for maturation when the need arises.
Dr Martin Reichard of the Czech Academy of Sciences Institute of Vertebrate Biology is interested in the aging process for wild animals, which means picking subjects carefully. Giant tortoises or Greenland sharks, for example, might give him little data before he retires.
Laboratory studies had found the killifish takes at least 18 days to become sexually mature, although unsuccessful mating attempts occur before this. There had been speculation that this was an exaggeration of wild development, with lab species having been artificially selected for fast growth, so as to make life easier for researchers.
Dr Reichard observed it in eight pools in southern Mozambique from January to May of 2016, reporting his results in Current Biology. He was surprised to discover the killifish sometimes grows up even faster in its natural environment, although the speed varies depending on the food available and density of competing fish.
The fish hatched just three days after water first began to fill the pools and in some places were sexually mature 14-15 days later, having reached sizes of up to 5.4 centimeters (2.2 inches). Unsurprisingly, once this occurs, they don’t muck around, breeding daily.
“We guessed that some populations of this species could achieve very rapid growth and sexual maturation under particular conditions," Reichard said in a statement. "But we have found that this rapid maturation is the norm rather than a rare exception."
As he anticipated, Reichard observed the fish pays a price for its rapid development, aging equally quickly and losing functional capacities at a point where other species would still be in their prime. The males, in particular, die young. Of course, this hardly matters if, by the time a fish has reached this point, the lake in which it lives is already drying up. Many of the pools Reichard studied dried up within 3-5 weeks of filling, but this was still enough time for them to seed the beds with eggs for the next rainy season.