Smallest Fish in the World: 7.9 mm, and Two Rivals

Bar chart drawn to scale of the smallest fish in the world, from a 6.2 mm male anglerfish to the 25 mm sinarapan, next to a 12 mm #8 octopus hook and a one-inch ruler — Drawing: fishing.info, from the sources listed on this page

The smallest fish in the world is Paedocypris progenetica, a see-through relative of the minnows that lives in peat swamps on Sumatra in Indonesia. Females are grown up at 7.9 mm (0.31 in), and the biggest one measured was 10.3 mm. Two other fish claim the title, and each wins by a different ruler. The lightest is the stout infantfish. The smallest single adult is a male deep-sea anglerfish.

Lay the world’s smallest fish on a #8 octopus hook and it’s shorter than the hook. It’s barely longer than the gap.

What is the smallest fish in the world?

Paedocypris progenetica is the shortest fish species, going by the smallest female found grown up. If you want one name you can repeat, use that one. It’s also the answer to “what’s the smallest freshwater fish”.

The trouble is that “smallest” can mean three things. It can mean the shortest species, the lightest species, or the tiniest single adult anyone has measured. Each one has a different winner, and all three sit within two millimeters of each other. The Australian Museum puts it plainly: which fish is smallest depends on your definition of small.

Here’s every fish with a real claim, and what you’d be measuring. Sizes are standard length, from the tip of the snout to the end of the backbone, with the tail fin left off. That’s shorter than the total length most state size limits use, which runs to the end of the tail.

Fish	Smallest grown-up	Largest known	Where it lives
Deep-sea anglerfish, male	6.2 mm (0.24 in)	Not given, his female was 46 mm (1.8 in)	Deep water off the Philippines
Stout infantfish	Males by 7 mm (0.28 in)	8.4 mm (0.33 in)	Great Barrier Reef and Coral Sea
Paedocypris progenetica	Females 7.9 mm (0.31 in)	10.3 mm (0.41 in)	Peat swamps, Sumatra and Bintan
Midget dwarfgoby	Eggs from 8 mm (0.31 in)	10.2 mm (0.40 in)	Reef drop-offs, Red Sea to the Society Islands
Dwarf pygmy goby	Males 9 mm (0.35 in)	Males 11 mm (0.43 in), females 15 mm (0.59 in) total length	Brackish water and mangroves, Philippines and Indonesia
Sinarapan	Males sometimes under 10 mm (0.39 in)	25 mm (1 in), total length	Lake Buhi and nearby lakes, Philippines

You’ll see the dwarf pygmy goby on a lot of smallest-fish lists. It’s tiny, but four fish in this table are smaller. The midget dwarfgoby, which FishBase lists as the dwarf atom goby, held the title before the 2004 and 2006 finds.

Why does the swamp fish win?

Paedocypris wins because it’s the shortest species when you count the fish that are grown up and breeding. The record is the smallest mature female, at 7.9 mm. The males netted with her ran 8.0 to 9.6 mm. A close cousin from Sarawak in Malaysia grows up at 8.8 mm and reaches 11.6 mm.

You won’t find them anywhere near a bass lake. They swim in slow, dark streams and pools in peat swamp forest, in the shade, a little above the bottom. The paper that named the fish calls that water highly acidic. The Associated Press report of the find gives a number, citing the researchers. The fish live in dark, tea-colored water with a pH of 3, it says, at least 100 times more acidic than rainwater. That’s sour water.

They also look like babies their whole lives. The body is see-through and keeps a larva’s shape into adulthood. The males carry a hard pad of skin just in front of their belly fins. The team thinks the pad and the fins work together as a clasp, maybe to hold a female. Ralf Britz, who helped describe them at the Natural History Museum in London, called Paedocypris “one of the strangest fish that I’ve seen in my whole career.”

Two tiny Paedocypris carbunculus fish on a black background, a red male above and a see-through female below, with a white scale bar of 1 mm

Paedocypris carbunculus from Central Kalimantan, Indonesia. It’s a close cousin of the record fish, not the record fish itself. Male above, female below. The white bar is 1 mm. Photo: Liu, Tan, Tan and Hong, PLOS ONE 2012 (CC BY 4.0), cropped

Count the scale bars along a fish in that photo. These two are about ten bars long, and the record fish is grown up at eight. The trouble is where they live. The team that named Paedocypris warned that the loss of the peat swamps puts it at risk. Britz said he hoped there’d be time to learn more “before their habitat disappears completely.”

What is the lightest fish?

The stout infantfish is the lightest. It lives on the Great Barrier Reef near Lizard Island and on Osprey Reef in the Coral Sea, off Australia. The paper that named it has males grown up by 7 mm. The largest one known, the only female, was 8.4 mm.

It’s far more slender than the other two, so it’s lighter. The Australian Museum puts one at less than a millionth of a kilogram. The museum adds a point you’ll like as an angler: game fish records go by weight, not length. Here’s the number you’ll remember: about 500,000 stout infantfish together would barely tip the scale at one pound.

Think about that next time you weigh a one-pound bluegill. Half a million of these reef fish would just about match it.

Only six were known when the fish was named in 2004. The first was caught near Lizard Island in 1979. It’s see-through, with no color except in its eyes, and it keeps the look of a baby fish as an adult. That’s where “infantfish” comes from.

The claim has a soft spot. The Paedocypris team wrote that only the 8.4 mm female was shown to be grown up, by her ripe eggs. The smaller males weren’t dissected.

An angler casting from the bank, silhouetted against golden sunrise fog

Casting into the sunrise fog. Photo: kalinovsky / Depositphotos.

What is the smallest fish in the ocean?

The smallest single grown-up fish ever measured is a male deep-sea anglerfish, Photocorynus spiniceps, at 6.2 mm (0.24 in). Guinness World Records lists him as the smallest fish and the smallest animal with a backbone. He was hauled up from 1,425 m (about 4,700 ft) in the Philippine Sea.

There’s a catch, and it’s a strange one. He was found fastened to the back of a female 46 mm (1.8 in) long. In five of the 11 families of these anglerfish, the tiny males bite onto a female and fuse to her for life. Tissue under the microscope showed he was a mature male, so he counts.

That’s why the other two have backers. The male anglerfish is one fish, the smallest one found, and the female he was on was more than seven times longer. Paedocypris and the stout infantfish are small as a species, males and females both. “There are always difficulties in talking about the smallest,” said Ted Pietsch, the University of Washington professor who described the anglerfish male. Is it length, volume or weight? “The debate goes round and round.”

So for the ocean, it depends again. The shortest adult is the male anglerfish. The smallest species, male and female, is the stout infantfish. Here’s how you can sort all three claims in one look:

If you measure	The winner	The number
The shortest grown-up species	Paedocypris progenetica	Females 7.9 mm (0.31 in)
The lightest species	Stout infantfish	About 500,000 to the pound
The smallest single adult	Deep-sea anglerfish, male	6.2 mm (0.24 in)
Guinness’s “smallest food fish”	Sinarapan	Up to 25 mm (1 in)

Pick the row that matches the question you were asked, and you’ve got the right answer.

Is the sinarapan the smallest fish?

No. The sinarapan from the Philippines grows to about 25 mm (1 in), roughly three times the length of the record holders. Its males are sometimes grown up at under 10 mm, FishBase says, so it’s tiny, but it isn’t the record. Its claim is different. FishBase notes it’s listed in the Guinness Book of World Records as the “smallest food fish”, the smallest fish caught to eat.

It lives in Lake Buhi and a few other lakes in Camarines Sur province, in the Philippines. Local fishermen catch it with fold-up push nets, and with palm leaves that draw the fish in for a three-cornered net. It’s a delicacy there. Overfishing threatens it, FishBase says, and so do fish brought in from elsewhere that eat it. It’s on the IUCN Red List, the world list of species at risk, as Vulnerable.

The dwarf pygmy goby also comes from the Philippines and turns up in the same searches. It’s smaller than the sinarapan: males reach 11 mm and females 15 mm. But FishBase says it’s considered extinct in the Philippines. The river where it was first found has since been reclaimed, and the water left there is heavily polluted.

Is a fish the smallest animal with a backbone?

Maybe not. In 2012 a frog from Papua New Guinea, Paedophryne amauensis, was described as the smallest known animal with a backbone. Its adults average 7.7 mm (0.30 in), with a range of 7.0 to 8.0 mm.

That’s an average, and the 7.9 mm of Paedocypris is the smallest grown female, so you’re holding two different rulers again. The 6.2 mm anglerfish male is smaller than any of the frogs, but he’s one fish. If somebody at the bait shop says the smallest backboned animal is a fish, he might be right. It depends which number he read.

What’s the smallest fish in US water?

US water has tiny fish too. The least killifish of the Southeast tops out at 1.4 in (36 mm). If you fish for panfish, the one to know is the orangespotted sunfish, which Iowa DNR calls the smallest sunfish. The agency says adults are grown at about 2 in (5 cm), and one over 4 in (10 cm) is very rare in Iowa. At spawning time the males color up so bright they “look like painted artificials”, in the agency’s words.

An orangespotted sunfish photographed side-on in a white tank, an olive body with orange spots and a blue cheek

Orangespotted sunfish from Illinois. Photo: moxostoma, iNaturalist via Wikimedia Commons (CC BY 4.0), resized

In Iowa you’ll find them most in man-made lakes, natural lakes and inland streams. They eat water insects, tiny crustaceans and now and then a small fish. Anglers do catch them: Iowa DNR’s record list has one of 3.62 in and 0.04 lb, caught in Frog Creek on May 28, 2024. So treat one like any panfish, with a bit of worm on a small hook. It’s a close cousin of the green sunfish and the bluegill.

The least killifish is one you’re unlikely to see on a hook. It lives in weedy, still or slow fresh and brackish water from the Cape Fear River in North Carolina to southern Louisiana. It’s one of the smallest animals with a backbone in the world that gives birth to live young. Despite the name, it’s no killifish. It’s a livebearer, in the same family as the mosquitofish and the sailfin molly.

US fish	How big it gets	Worth knowing
Least killifish	Up to 1.4 in (36 mm)	Gives birth to live young, NC to Louisiana
Mosquitofish, female	Up to about 2.8 in (70 mm)	The biggest of North Carolina’s four livebearers
Orangespotted sunfish	Grown at about 2 in (5 cm), rarely over 4 in (10 cm) in Iowa	Iowa DNR calls it the smallest sunfish. Iowa record: 3.62 in, 0.04 lb

How small is that next to your tackle?

Smaller than you’d guess. A Mustad #8 octopus hook is 12 mm (0.47 in) long with a 7.4 mm gap. Sizes #10 to #6 are the range for panfish and for trout on bait. You can see every size of it on our hook size chart.

Put the record fish next to that hook. The male anglerfish at 6.2 mm would fit inside the gap. The stout infantfish at 7 mm would too, barely. The Paedocypris female at 7.9 mm sticks out of the gap by half a millimeter, and she’s still two-thirds the length of the hook.

Here’s the quick way to picture it at the water:

The record fish are about 5/16 of an inch long. That’s the mark just past the quarter inch on a tape.
A #8 hook, at 12 mm, is longer than every fish in the record race.
The sinarapan, Guinness’s “smallest food fish”, is about one inch, twice the length of that hook.
A grown orangespotted sunfish, at about 2 in, is some six times longer than the record holder.
Half a million stout infantfish weigh about what one one-pound bluegill does.

What these record fish share is out-of-the-way water: a sour peat swamp, a reef far offshore, the deep sea. For how a fish this size can still lay eggs, see how fish reproduce. The fish facts page answers the other questions kids ask on the way to the water.

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