Earth’s waters are filled with billions of fish, coming in all manner of glorious colors, shapes, and sizes – but which is the smallest fish of them all? It turns out that question isn’t so easy to answer.
The smallest fish in the world
One of the strongest contenders for the smallest fish is Paedocypris progenetica. The smallest mature female of this species was found to be just 7.9 millimeters (0.31 inches) long – that’s smaller than the average length of a fingernail, and by a good few millimeters too.
This tiny female isn’t an anomaly either; in the study detailing the discovery of the species, the biggest female that the researchers found in one of their samples was still only 0.4 millimeters (0.02 inches) bigger than the smallest.
Male members of P. progenetica are thought to have a maximum size of 9.8 millimeters (0.39 inches) and for the species as a whole, just 10.3 millimeters (0.41 inches) – even in the tiniest of animals can be found a great example of males not always being bigger.
The minuscule species, which belongs to the carp family, can be found in highly acidic, blackwater peat swamp forests in Sumatra and Bintan Island, Indonesia.
However, it’s estimated that the population of P. progenetica is decreasing due to deforestation and habitat degradation in these areas. As a result, the species is now considered as “Near Threatened” by the IUCN Red List.
Another contender?
If we go off the length of just one individual fish and disregard its sex, then technically, there is a smaller fish out there. Research from William Watson of the National Oceanic and Atmospheric Administration Fisheries and the now retired H.J. Walker of the Scripps Institute of Oceanography suggests that the title should belong to Schindleria brevipinguis, the stout infantfish.
Mature male stout infantfish identified in their 2004 study measured between 6.5 to 7 millimeters (0.26 to 0.28 inches) and the largest specimen of all was just 8.4 millimeters (0.33 inches) – nearly 2 millimeters (0.08 inches) smaller than the maximum size for P. progenetica. It’s light too, with the smallest specimen weighing only 0.7 milligrams.
Trouble is, the stout infantfish is only known from six specimens, all found in the Great Barrier Reef. In comparison, just a single one of the P. progenetica samples taken during their discovery contained 56 specimens alone. As such, the limited number of assessed specimens of S. brevipinguis makes it difficult to say for sure that it is indeed the smallest.
At the time of both studies, the authors proposed that the fish could also be the world’s smallest vertebrate. However, more recent research has blown that out of the water – as far as science knows, the teeny tiny crown appears to belong to an adorably small flea toad.
