No larger than a human fingernail, scientists have identified the world's tiniest fish.

The ocean covers a vast portion of the planet's surface and is home to billions of different fish species — some are enormous, while others are tiny; they can be of various colors, and the appearance of certain species at the ocean's surface is sometimes perceived by people as a "harbinger of apocalypse," according to IFLScience.

But which of this diversity is actually the smallest fish in the ocean? Scientists warn that answering this question is not straightforward, but they do have a few contenders.

One of the leading candidates for the title of the smallest fish in the ocean is Paedocypris progenetica. Research shows that the smallest mature female of this species measures only 7.9 millimeters in length — for comparison, that is smaller than the average length of a fingernail.

Scientists state that this tiny female is not an anomaly for its species. The team found that the largest female of this species they could locate was only 0.4 millimeters larger than the smallest one. It’s worth noting that the normal sizes for Paedocypris progenetica are 9.8 mm for males and 10.3 mm for females.

This minuscule species, which belongs to the carp family, can be found in highly acidic blackwater peat swamp forests on Sumatra and Bintan Island in Indonesia. Unfortunately, their population is relentlessly declining due to deforestation and habitat degradation.

According to William Watson from the National Oceanic and Atmospheric Administration's fisheries division, technically, there exists an even smaller fish in the world. Scientists believe this title might belong to Schindleria brevipinguis.

Adult males of this species, as shown in a 2004 study, reach lengths of 6.5 to 7 mm, with the largest recorded specimen measuring only 8.4 mm. Interestingly, the weight of the tiniest specimen was also 0.7 milligrams.

The main issue is that Schindleria brevipinguis is known to science only from six specimens found on the Great Barrier Reef. In comparison, only one of the P. progenetica specimens collected during their discovery contained 56 individuals. As a result, the limited number of specimens does not allow scientists to assert that Schindleria brevipinguis is the smallest fish in the ocean.