Researchers have yet to conclusively determine whether the world’s smallest fish is Paedocypris progenetica or Schindleria brevipinguis, partly due to the limited number of specimens available.
Paedocypris progenetica, a member of the carp family. (Photo: Apfish).
One of the strongest contenders for the title of the smallest fish is Paedocypris progenetica. The smallest mature female of this species measures only 7.9 mm, shorter than the average length of a fingernail. In a detailed study describing the discovery of P. progenetica, the largest female found was only 0.4 mm longer than the smallest specimen, according to IFL Science. Male P. progenetica can reach a maximum size of 9.8 mm.
Belonging to the carp family, P. progenetica inhabits the acidic blackwater peat swamp forests on the islands of Sumatra and Bintan in Indonesia. However, it is estimated that the population of P. progenetica is declining due to deforestation and habitat degradation in these areas. As a result, it is currently listed as “near threatened” in the International Union for Conservation of Nature (IUCN) Red List.
When considering size across species regardless of sex, researchers have noted a smaller fish species. A study by William Watson at the National Oceanic and Atmospheric Administration (NOAA) reveals that the title of the smallest fish belongs to Schindleria brevipinguis.
Mature male S. brevipinguis identified in a 2004 study measured only 6.5 to 7 mm, with the largest specimen reaching just 8.4 mm, which is nearly 2 mm smaller than the maximum size of P. progenetica. Additionally, it is very light, with the smallest specimen weighing just 0.7 milligrams. However, only six individuals of S. brevipinguis are known, all of which were collected from the Great Barrier Reef. In contrast, one specimen of P. progenetica that researchers collected upon discovering the species contained 56 individuals. The limited number of specimens makes it very challenging to draw definitive conclusions about the smallest fish.
