How Small is the Smallest Fish?

The smallest fish in the world is the Paedocypris progenetica. The adult females measure 7.9 mm (.31 in).

Classification of the Paedocypris

The Paedocypris refers to the Indonesian genus within the Cyprinidae family (this one also includes carps). Aside from Paedocypris progenetica, another genus is the Paedocypris micromegethes. A third species was reportedly seen in 2006 off Terengganu, Malaysia.

Discovery of the Paedocypris

The Paedocypris progenetica and the Paedocypris micromegethes were discovered in 1996. The identification was done by Tan Heok Hui (of the Raffles Museum of Biodiversity Research and the National University of Singapore) and Maurice Kottelat (Switzerland). The world’s smallest fish has also been reportedly seen off Sarawak.

Most of the time they are to be found in backwater streams.
The name was derived from the Greek word paideios referring to children. Cypris is the Greek word for Venus. The word progenetica was derived from the word progenetic.

Physical Attributes

The Paedocypris looks very different from the other fish. It doesn’t have the bony structure surrounding the brain. Moreover the fish maintains the post-anal larval fin fold. This is just around the ventral edge of the caudal peduncle.

This feature is often found in fish larvae. The males are also noted for the pelvic fins. The first ray ends in a hook of keratinized skin. This is backed by the hypertrophied pelvic musculature.

The keratinized skin is also present at the pelvic fin. Although certain facts about the world’s smallest fish are known, the purpose of these fins is still unclear.

The prevailing theory is the male employs them during mating. It is used to secure the female. Other scientists suggest it is utilized to maintain position at a spawning surface. Only further research will uncover its true purpose.

Habitat of the Paedocypris

To this date, the Paedocypris progenetica has been found mainly in the peat swamps at Sumatra, Indonesia. The Paedocypris micromegethes on the other hand, has been spotted at Sarawak (Borneo), also in peat swamps. Owing to their dimensions, both types of Paedocypris can flourish during droughts.

It has been shown they can survive in puddles of acid water. Even with a pH level of 2.9, the Paedocypris can thrive. The world’s smallest fish however, is being threatened with extinction. This is due to the destruction of rainforests and pollution of the waters.

Note: some claim that some species of the anglerfish Photocorynus spinicep is much smaller than the Paedocypris progenetica. It is true that some of its members measure 7.3 mm and even 6.2 mm.

However, these fishes survive by way of sexual parasitism only. It should also be pointed out that the female members of the species can grow as much as 50.5 mm. But while a lot of scientists and researchers accept the Paedocypris progenetica as the smallest, others are still not certain.

The questions of what the world’s smallest fish is may take some time to settle. But until evidence comes up indicating otherwise, the Paedocypris progenetica will be regarded as the one by most researchers.