Smallest Fresh Water Fish

The smallest freshwater fish in the world is Paedocypris progenetica. The smallest specimen ever measured is 7.9 mm long. The fish can be found in the swamps of Sumatra, Indonesia.


The species is classified under the carp family. The scientific name is Paedocypris progenetica. The fish is also the smallest backboned animal ever known.

Appearance and Habitat

The fish is see-through and look like larvae. The head skeleton is small and the brain is not protected by any bones. Studies reveal Paedocypris progenetica dwell in tea-colored waters.

The acidity level is pH3. This makes it 100 times more acidic compared to rainwater. Its habitat has continued to puzzle scientists. It is one of the very few creatures that can live in such acidic places.


The smallest freshwater fish was discovered by Tan Heok Hui of Raffles Museum of Biodiversity Research in Singapore and Maurice Kottelat. Together with Ralf Britz of the Natural History Museum and Kai-Erik Witte, they were able to analyze the fish’s pelvic fin and structure.

The Indo Pacific Goby

The Indo Pacific goby used to be regarded as the world’s tiniest fish. The fish have a maximum length of 24 mm.

Other Information about Paedocypris

There are three species known: Paedocypris progenetica, Paedocypris micromegethes and a third one discovered in 2006. The third species was seen at Terengganu, Malaysia. The largest ever measured is 10.3 mm.

Aside from the size, there are other aspects that set it apart from other fish. The lack of a skull structure for the brain is just one aspect. The fish also keeps the post-anal larval-fin-fold at the caudal peduncle.

The fish is also noted for its distinct sexual dimorphism. Their pelvic fins are also unique. The ray terminates with keratinized skin that resembles a hook. The purpose of the keratinized skin on the males is subject to debate and interpretation. One of the most popular theories is that they are used when courting females.

Photocorynus Spiniceps

The male Photocorynus spiniceps are said to be only 6.2 to 7.3 mm long. But these are only able to live by way of sexual parasitism. The female members of these species also reach lengths of 50 mm.

Research on the smallest freshwater fish is difficult to do owing to their size and scarcity. An even bigger problem is the threat posed to their environment by human activities. Efforts to preserve their habitat are now ongoing.

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