What is the smallest fish in the world?

Fish are wonderful creatures of all shapes and sizes. We tend to be familiar with the biggest fish in the world - which is, of course, the whale shark. But do we ever give much thought to our pint-sized pals?

Actually, the smallest fish in the world is far smaller than a pint, so perhaps that is the wrong descriptor for them! Luckily for you, we have done that research and found some of the top contenders for the esteemed title of the world's smallest fish. Keep reading to find out more … 

Before we dive into the contenders for smallest fish in the world, it is worth bearing in mind that the winner of that title may vary depending on whether by smallest you mean in length, or weight or even in width.

This article has considered all three of these factors when attempting to find the titleholder, but other sources may cite different winners of this respected prize. 

….and the winner is….or should that be ‘winners are’?

Paedocypris progenetica

Paedocypris progenetica is a recently discovered teeny, tiny fish known as a dwarf minnow. This little guy has been thought by many to be the smallest fish in the world.

It was discovered in the swamps of Sumatra, a small island in Indonesia. We say “little guy”, but it is the female fish that gets the fame for this. The female fish reaches around 7.9mm at full maturity which is less than one-third of an inch.

This tiny measurement is what is making the fish a top contender in the eyes of many researchers for the title of smallest fish in the world. 

The Paedocypris progenetica belongs to the large carp family. The minute minnow is completely see-through, meaning you can see its tiny skeletal frame, and even its brain and other organs. They almost look like larvae in appearance because of their shape and size. 

The swaps in which it lives is what is known as a peat swamp. The acid level of the water is 100 times more than rainwater at pH3! These are definitely some hardy little critters. 

Schindleria brevipinguis

Schindleria brevipinguis is yet another new discovery in the fish kingdom. Many experts think that this little fish has dethroned the Paedocypris progenetica. However, there is much debate over which is smaller because of how similar they are in size, and there being just fractions of millimeters in it. 

It is 7mm in length, at least, the male fish are. The female fish grow to the size of 8mm, slightly bigger. 

The fish lives in the waters around the relatively recently discovered Australian island of Lizard Island which was discovered just over 40 years ago in 1979. The species itself was only discovered in 2004, making it a slightly more recent discovery of that of the Paedocypris progenetica. 

Not only is this fish thought to be one of the shortest, but also it may even be one of the lightest in weight, with the Stout Infantfish coming in at under one-millionth of a kilogram. They are relatives of gobies, another type of fish, and are known as a Stout Floater. 

Photocorynus spiniceps

Photocorynus spiniceps is the last fish on our list of contenders for the smallest fish in the world. This is another fish that has one sex who is bigger than the other. The male is tiny, coming in at 6.2mm. The female on the other hand is humungous in comparison, with an average size of 46mm. The male lives off of the female, acting as a parasite! 

Many experts argue that this species doesn’t count because of the huge difference between the two sizes - female and male. Others, however, don’t think that both sexes of a breed need to be considered, and having this one tiny fish is enough to win the whole species the title. 

Our final word

So, it seems there are three very strong contenders for the title of the smallest fish in the world. The Paedocypris progenetica, Schindleria brevipinguis, and Photocorynus spiniceps are all worthwhile considerations for this claim.

It seems next to impossible to come up with just one winner, especially given the various ways this can be measured. Of course, if we go by mere length, the Photocorynus spiniceps is the clear winner.

However, due to the fact that it is only the male that could possibly be a contender, many people think that this species is undeserving of the title.

We could then consider the weight of the fish. In this case, the winner is likely to be the Schindleria brevipinguis due to its minuscule weight. This species also has the bonus of having a tiny male and female, with both of them coming in at 8mm and well under.

However, they are extremely close in size to the also newly discovered Paedocypris progenetica. This puts a huge debate over the two, again. 

Speaking of the Paedocypris progenetica, the relative of the carp family, this little fish is certainly a great contender. The tiny female fish is 7.9mm or less in general. The male fish is slightly larger, though, at 10.3mm. Clearly, coming up with a definitive, single species, is going to prove difficult. 

Suffice to say, many experts tend to give all three this much-desired title of smallest fish in the world. For us, it is totally dependent on the conditions.

However, at the moment, the Schindleria brevipinguis seems to be in the lead, due to both male and female being under 8mm, and it having the advantage of being the lightest fish on the list. 

Whatever your personal opinion may be, we are sure that you can now understand the constant debate and confusion, especially because two of the contenders are very recent discoveries in the animal world.

One thing is for sure, and that is the fact that there is still a lot to be learned about all three of these animals.