It is difficult to identify the world’s smallest fish

One of the strongest contenders for the title of smallest fish is Paedocypris progenetica. The smallest adult female of this species is only 7.9 mm long, smaller than the average length of a fingernail. The study describes the fish discovery in detail P. progeneticathe largest female that scientists found in the sample was only 0.4 mm larger than the smallest, according to IFL Science. Male P. progenetica fish have a maximum size of 9.8 mm.

Belonging to the carp family, P. progenetica inhabits the highly acidic blackwater peat swamp forests of the Indonesian islands of Sumatra and Bintan. However, P. progenetica populations are estimated to be decreasing due to deforestation and habitat degradation in these areas. As a result, they are now listed as “near threatened” on the International Union for Conservation of Nature (IUCN) Red List.

If considering the length of an individual and regardless of gender, researchers note a smaller fish. Research from William Watson of the US National Oceanic and Atmospheric Administration’s Fisheries Division revealed that the title of smallest fish belongs to Schindleria brevipinguis.

Adult male S. brevipinguis identified in a 2004 study were only 6.5 – 7 mm long, and the largest specimen was only 8.4 mm long, nearly 2 mm smaller than the maximum size of P. progenetica. It’s also very light, with the smallest specimen weighing 0.7 milligrams. However, S. brevipinguis is known from only six individuals, all from the Great Barrier Reef. Compared to them, a sample of P. progenetica that the researchers collected when discovering the species contained 56 individuals. The number of individuals for evaluation is limited, so it is difficult to draw firm conclusions about the smallest individual.