What is the smallest fish in the world?

Out of the many animals that float within the waters of our world's oceans, few are more overlooked than the smallest among them. The world's smallest fish, though, is a remarkable animal that deserves more attention than its body size would suggest!

The smallest fish in the world is even tinier than the red neon, a popular ornamental fish.
The smallest fish in the world is even tinier than the red neon, a popular ornamental fish.  © 123RF/lapis2380

Tens of thousands of fish species, if not millions, inhabit the waters of our vast planet.

There are so many of these tiny finned things out there that we haven't even discovered them all, opting to instead focus on getting to know a few of them a little bit better than others.

Yet, there are some fish that few have heard of for a different reason – they're absolutely tiny.

Dog wreaks hilarious chaos on the family car after muddy romp!
Dogs Dog wreaks hilarious chaos on the family car after muddy romp!

So which flippered-fellow has taken home the animal world record for being the smallest fish in the world?

What's the world's tiniest fish, and why is it so ridiculously miniscule?

What's the world's smallest fish?

The paedocypris progenetica, more commonly known as the dwarf minnow or the dwarf danios, is considered the world's smallest fish at approximately 0.41 inches in length. These tiny little fish are about the size of a mosquito and extremely hard to see on account of both their size and their translucent appearance.

Native to the peat swamps and forests of Southeast Asia – specifically Sumatra and the Indonesian province of Bintan – these tiny little dudes are members of the carp family and generally live in water that is low in oxygen and highly acidic. This gives them a very unique environment and one that is unfortunately very easily disrupted by environmental changes.

In general, the dwarf minnow will tend to swim deep in the water, where cooler layers of water move very slowly and are seldom replaced with water of a higher pH level. Very little is known about these strange and tiny little creatures but, at such a tiny size, it isn't surprising that they hold a world record for being the world's smallest fish!

So, let's take a look at a few details about paedocypris prognetica, the smallest fish in the world:

  • About their size: Dwarf danios are by far the smallest fish in the world. Considered a "dwarf" fish, they don't end up much larger when they're fully grown than most other fish species are as larvae. The average length of a female is slightly bigger than the male at 0.41 inches to a male's 0.39 inches.
  • About their color and transparency: These tiny little fish are more-or-less entirely translucent. This would make them nearly impossible to see if it weren't for their slightly reddish coloration, which stands out against the sand.
  • About their skeletons: The paedocypris progenetica has no scales or sensory organs. As such, their skeletons take on a very different form to most other fish, making them very fragile.

As the smallest fish in the world, combined with the fact that they live in secluded and hard-to-find places, it makes sense that very few people have ever seen them in the wild with their own eyes!

The dwarf minnow is not only the world's smallest fish, but also one of the most fascinating!
The dwarf minnow is not only the world's smallest fish, but also one of the most fascinating!  © Imago/Blickwinkel

Why is this tropical fish so small?

The dwarf minnow, or paedocypris progenetica, is small due to its environment in the murky backwaters of Southeast Asia. This is quite an extreme environment, especially due to the high acidity in the water and the extremely low oxygen. It is such a difficult place to live and grow, in fact, that these areas are home to many different varieties of miniature fish.

According to a study published in 2018, it was theorized that "the extreme environment in which these fish live imposes resource limitations that may favor a smaller genome size." Admittedly, this remains just a theory and is by no means definitive proof.

It does make sense, however, as the extreme environment would change the way that fish develop. As is exemplified in the study, while these little dudes are very similar to the zebrafish, they never developed skeletons. This is likely because of the low pH in the water and the lack of oxygen.

It is not an area that has been extensively studied, likely because the paedocypris progenetica is unlikely to have any influence on humanity. Still, it doesn't seem so surprising that such a harsh environment would produce a harsh result.

The smallest fish in the world is endangered

Due to accelerating habitat loss at the hands of human activity, these tiny little guys are on their way toward becoming critically endangered. As a result of drainage issues in peat swamp forests as well as land clearing and palm oil plantations, these fish are dying at an alarming rate and sadly may not be around for very much longer.

Part of the problem, of course, is that these fish are so small that very few people are going to notice if they're gone. After all, you're not going to fish for such a small animal, so why worry about it dying out?

Well, considering how important they are for their local ecosystems, there might be a lot to worry about. We'll just have to wait and see – and do what we can to help our planet's ecosystems while we can.

Cover photo: 123RF/lapis2380

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