4 Smallest Fish in the World

Meet the four smallest fish in the world! These swimmers are so tiny, you would need a magnifying glass to see them up close.

Oct 26, 2023By Natasha Elder
smallest fish in the world

The ocean is home to a massive array of fish in every shape, color, and size imaginable. Some, like the whale shark, Southern sunfish, and Beluga sturgeon are huge. Others are so small you would struggle to spot them without a magnifying glass. Here, you can meet four of these small swimmers for yourself––all of which measure less than an inch long!

1. Photocorynus Spiniceps

male photocorynus spiniceps fused
Image credit: Australian Museum

Have you ever asked yourself what the smallest fish in the world is? Wonder no more. Meet the male photocorynus spiniceps. Measuring a measly 0.24 to 0.29 inches (6.2 to 7.3mm), this tiny little fella is a type of anglerfish that lives in the bathypelagic zone of the deep sea in both tropical and subtropical water.

Like other creatures that live this far down in the depths, this minuscule male is so lightly pigmented that he appears translucent. He has slightly tubular eyes, along with inflated olfactory organs. Aiding in his “barely there” appearance is the fact that his spine is not developed, so he sort of looks like a piece of soggy tissue paper flowing with the current.

What truly makes the male photocorynus spiniceps one of the most interesting deep sea creatures around is that he spends the vast majority of his life fused to the back of a female in a parasitic manner. Female photocorynus spiniceps grow to lengths up to 2 inches (50.5mm) – that’s around 721% larger than her male hanger-on. The females are responsible for all the swimming and hunting, while the male’s only job is to help her reproduce. And this isn’t a monogamous animal pairing; a lone female photocorynus spiniceps can have up to eight males attached to her back!

2. Stout Infantfish

male stout infantfish translucent
Image credit: Fish Base

Next up is the stout infantfish, or the schindleria brevipinguis, a species of fish with a standard length of 0.30 inches (7.7mm) and a maximum length of 0.33 inches (8.4mm.) Before the photocorynus spiniceps was discovered in 2005, the stout infantfish held the title of the world’s smallest fish. The stout infantfish is an epipelagic zone dweller that is only found in Australia’s Great Barrier Reef.

Comparatively, stout infantfish are thicker, or stouter, than other types of infantfish. The stout infantfish is transparent, which is unusual for epipelagic fish, and features a pair of bulging beady black eyes. This unusual fish also has no teeth and lacks the traditional scales most fish have.

There are only six known specimens of stout infantfish in the ocean, making them extremely rare. Despite their tiny number, they are not classed as endangered; they just aren’t a populous species. The stout infantfish is the polar opposite of immortal jellyfish, big-mouth buffalo fish, and other animals that have lived for hundreds of years. What is fascinating about the stout infantfish is that its entire lifespan is just two months. Size, number, lifespan – everything about these little guys is on the small side.

3. Paedocypris Progenetica

paedocyrous progenetica acid swamp aquarium
Image credit: Fishi-Pedia

Paedocypris progenetica is a member of the tiny carp family, and it is tiny indeed. The male paedocypris progenetica reaches a maximum length of 0.39 inches (9.8mm), and the smallest specimen recorded was a female that measured in at just 0.31 inches (7.9mm) long. Remarkably, this species is exclusive to around 20 incredibly acidic small blackwater peat swamps in Indonesia.

Like other small fish, the tiny paedocypris progenetica is colorless. Because of its translucency, you can see all of its internal organs, meaning that in certain light (and when they’ve eaten certain foods) this fish appears red or purple.

Sadly, the paedocypris progenetica is a threatened species that was added to the International Union for the Conservation of Nature’s (IUCN) Red List in 2019. This is due to the rapid loss of blackwater peat swamps in Indonesia and Southeast Asia as a whole. Surprisingly, this incredible little fish occasionally pops up for sale but is NOT a beginner-friendly fish by any stretch of the imagination and should only be kept by expert fish keepers and aquarists.

4. Dwarf Pygmy Goby

dwarf pygmy goby phillippine goby fish
Image credit: Fish Base

Last up is the dwarf pygmy goby, also known as pandaka pygmaea or the Philippine goby. These miniature males measure in at 0.35 to 0.43 inches (0.35 mm to 0.43 mm) while females typically reach lengths of 0.59 inches (1.5cm). The dwarf pygmy goby was first discovered in the Philippines where it lived in the shallow waters of shaded riverbanks.

Like all of the other fish on this list, the dwarf pygmy goby is transparent – but it has several dark brown spots across its body that make it recognizable. Once upon a time, this fish was the national fish of the Philippines before the milkfish came along. If you enjoy fun fish facts, you’ll love this: a life-size etching of the dwarf pygmy goby was once depicted on ten centavo coins in the Philippines.

Dwarf Pygmy Goby: Saved from Extinction?

pygmy goby on a coin
Image credit: Wikimedia Commons

The riverbanks where the dwarf pygmy goby was once endemic to were reclaimed and this tiny creature was thought to be extinct as a result. Thankfully, in 2006, it was rediscovered in other areas of the Philippines, as well as in Bali and Singapore. One could argue that this nano fish was brought back from extinction.

Though no longer thought to be endangered, the ICUN doesn’t have enough information on the conservation status of this fish and has classified it as Data Deficient. Like in the case of the paedocypris progenetica, experienced aquarists can keep the dwarf pygmy goby. Considering this fish was recently considered extinct, it’s best to leave caring for it to the professionals.

Natasha Elder
By Natasha Elder

Natasha is a mother, a wife, a writer, and a serial cat owner. Though she is currently in mourning, her heart not ready for another feline family member just yet, she has always lived life with four paws beside her. She loves – you guessed it – cats, as well as creatures of the fluffy, scaly, and finned variety. Natasha longs to meet Sir David Attenborough one day and is passionate about responsible pet ownership