Japanese Pygmy Seahorse

FishEast Asia

Oct 21

Written By Alexander Julius Jensen

Hippocampus japapigu

The Japanese pygmy seahorse is the size of a grain of rice — about 1.6 cm long (0.6 in) — among the smallest seahorses in the world. It wasn't formally named until 2018, whereupon it received the specific title of "japapigu" or "Japan pig", because locals think it resembles a baby pig.

Hippocampi

Clockwise from top left; zebra seahorse (*Hippocampus zebra*), long-snouted seahorse (*H. guttulatus*), spiny seahorse (*H. histrix*), and big-belly seahoreses (*H. abdominalis*)

There are almost 50 known seahorse species that inhabit our planet's calm coastal waters. Their genus, Hippocampus ¹, comes from the Greek hippos, meaning ‘horse’, and kampos, meaning ‘sea monster’. A seahorse's elongated head, terminating in a tube-like snout, vaguely resembles the muzzle of a horse, but I think the latter epithet is more illustrative. These are marine monsters; strange sea serpents and water dragons.

Their skin is plated in bony armour, contorted into odd ridges and spines. Their curling, serpentine tails grasp corals and seagrass. Their colours are black, purple, red, green, and gold. Like rainbow apparitions, their forms shimmer and shift from one hue to another — in the face of danger, fading to hide; in a dance with a lover, flushing with pride. In splendour and mystique, they surpass any sea monster of myth or hoofed creature on land.

The Pygmy Pig

If most hippocampi are horses of the sea, then the eight pygmy seahorses more closely resemble newborn ponies — or, if you ask someone from Japan, tiny baby pigs.

Hippocampus japapigu, the Japanese pygmy seahorse, grows to a maximum length of 1.6 cm (0.6 in) — the size of a rice grain. It clings to soft coral and algae with its prehensile tail, appearing like an extension of the reef itself. Its beige body is spattered with patches of pink, dotted with black, and overlaid with a lattice of meandering white lines — a paisley-like pattern.

It's found in the coastal waters of southeastern Japan, but for a long time, it remained hidden — just a tiny strip of seaweed swaying with the current. This pygmy species was known to Japanese scuba divers but, until very recently, unknown to science. Only in 2018 was it formally described and bestowed with the specific name japapigu, which means "Japan pig". Rather than the long, horse-like muzzles of other seahorses, this pygmy has a squished, squat, piggy snout.

Small Seahorses

Japanese pygmy seahorses; (A) male and (B) female.

There are currently eight known species of pygmy seahorse. They’re mostly scattered throughout the shallow waters of Southeast Asia — although, there is one exception. They are anatomically distinct from their larger relatives; rather than a pair of gills, they each have a single gill opening on the back of their heads, and the males brood their young in pouches located on their trunks, rather than on their tails.

They are clever and shy; often hiding in plain sight amidst corals and seagrass. Some are travellers, swimming about by furling and unfurling their tails, while others are homebodies, choosing one spot and settling down forever. They are also social, convening in assemblies of over 20 seahorses, where they've been seen warping their tails around each other — a friendly "hug" or a show of dominance?

No other group of seahorses is as adorable as the pygmies. And no other seahorses are as small.² But which is the very smallest seahorse species?

The Smallest of the Small

From top to bottom; Coleman’s pygmy seahorse (*Hippocampus colemani*), Denise’s pygmy seahorse (*H. denise*), and (*H. bargibanti*).

The heftiest of the pygmies is Coleman’s pygmy seahorse, which can grow to a behemoth size of 2.7 cm (1.1 in), with a pale white or yellow body, typically splotched with patches of growing algae. This species is thought to be exclusive to the waters of Lord Howe Island off the east coast of Australia, however, it might also range much further afield; to eastern Papua New Guinea and Taiwan perhaps. The same goes for other pygmy seahorses with restricted ranges. It's probable that they populate wider parts of the ocean than we know, living in less-dived waters, where no one has looked for tiny seahorses clinging to algae and coral.

Then there is Denise’s pygmy seahorse, which floats around at a length of 1.3 cm (0.5 in). Eventually, it chooses a gorgonian coral, grasps on with its tail, and remains there for the rest of its life — growing to its full size of 2.4 cm (0.9 in). This seahorse ranges widely throughout the Western Pacific Ocean and can live as deep as 90 metres (295 ft) — which is deep for a seahorse. It exhibits as much colourful variety as its host corals, appearing like just another one of a coral's many branches, tubercles and all.

Bargibant’s pygmy seahorse also clings to coral — coming in two distinct colour morphs (one pale grey-purple and one yellow) that mimic its coral hosts — and it also grows to be 2.4 cm (0.9 in) long. This was the first pygmy seahorse ever discovered, and quite by accident. In 1969, the naturalist Georges Bargibant stumbled upon it in the waters of New Caledonia while examining a gorgonian sea fan.

From top to bottom; Sodwana pygmy seahorse (*Hippocampus nalu*), Walea soft coral pygmy seahorse (*H. waleananus*), and Pontoh’s pygmy seahorse (*H. pontohi*).

The Sodwana pygmy seahorse grows to be 2 cm (0.8 in) long and looks a lot like the Japanese — despite living in the shallow waters of Sodwana Bay, all the way over in South Africa. Its specific name, nalu, means “here it is” in the local Xhosa and Zulu languages, denoting that the species had been there the whole time, we just needed a keen observer to discover it. This is the first true pygmy seahorse found in Africa.

Back in Asia, in the waters surrounding Walea Island in Sulawesi, Indonesia, lives the Walea soft coral pygmy seahorse — which measures 1.8 cm (0.7 in) long. The "soft coral" in its name refers to the Nephtea soft coral, which it commonly clings to with its tail. But this tiny traveller has also been seen swimming grand distances (for a pygmy seahorse) from one coral to another.

Here, in the rankings of the known pygmy species, sits the "Japan pig" with a maximum length of 1.6 cm (0.6 in). It is just barely larger than Pontoh’s pygmy seahorse at 1.5 cm (0.6 in). Pontoh’s pygmy prefers grasping onto grasses, rather than clinging to coral. It ranges throughout the Indonesian and Philippine archipelagos and are often seen in pairs, living within seaweed meadows. Unfortunately, ocean acidification has degraded many such meadows, and many Ponthoh's pairs have been forced to move and adapt.

Satomi’s pygmy seahorses (*Hippocampus satomiae*) — the smallest known seahorse species in the world.

Finally, the smallest of all pygmy and non-pygmy seahorses, at the very pinnacle of puniness, is Satomi’s pygmy seahorse — with a maximum length of 1.4 cm (0.55 in). It is less flashy than its relatives, usually a beige or brow, and often appears partially translucent. It is also exceptionally active. This species is scattered in patches throughout the western Pacific Ocean and, unsurprisingly, it is very hard to find. This seahorse seems to vanish during the day, even in areas where it's known to live. It comes out after dark, gathering in groups of 3 to 5 and hosting nightly meetings held atop small sea fans.

It's very likely that more pygmy seahorse species exist, undiscovered and undescribed, out there in our oceans. This tiny branch of the seahorse family has only recently begun to be mapped; from Bargibant’s in 1969, to Satomi’s in 2008, the Japanese in 2018, and the Sodwana in 2020. Maybe we'll even discover a new tiny-record-holder, more minuscule than Satomi’s seahorse. Afterall, the smaller the seahorse, the harder it is to find. So, if you want to discover a new species of hippocampi, grab your diving gear and a magnifying glass, and embark on a search of coral reefs and seagrass meadows to find the next pygmy seahorse.

A mythological hippocampus on the left and an anatomical hippocampus on the right.

¹ The word hippocampus brings to mind one of two things; a horse-fish creature from Ancient Greek mythology or brain anatomy.

The hippocampi of Greek myth are chimaera creatures — with the fore parts of a horse and the hind parts of a serpentine fish — and were often depicted as the mount of the sea god Poseidon. Did the Ancient Greeks draw inspiration from real marine fauna? The mythological sea horse was certainly named before the real thing (the genus Hippocampus was first described in 1810), but it's possible that the myth was at least inspired by real-world seahorses.

On the other hand, the hippocampus of the brain — responsible for memory, learning, and emotion — was definitely named after seahorses, for the simple reason that this cerebral structure is sort of shaped like one.

A dwarf seahorse (*Hippocampus zosterae*).

² If it wasn't for the pygmy seahorses, the smallest species would likely be the dwarf seahorse (Hippocampus zosterae). In appearance and anatomy, the dwarf is more in line with full-sized seahorse species; with a pair of gill openings on the sides of its head and a brood pouch on its tail. It lives in the coastal waters of the western Atlantic Ocean and grows to a maximum length of 5 centimetres (almost 2 inches).

**Where Does It Live?**

⛰️ Subtropical and temperate reefs, at depths between 5 - 22 metres (16 - 72 ft).
📍 Central and southwestern Japan, to Taiwan and possibly southeastern China.

Size // Tiny
Length // Maximum 1.6 cm (0.6 in)
Weight // N/A
Activity: N/A
Lifestyle: N/A
Lifespan: N/A
Diet: Plankton
Favorite Food: Tiny crustaceans 🦐
Class: Actinopterygii
Order: Syngnathiformes
Family: Syngnathidae
Genus: Hippocampus
Species: H. japapigu

This seahorse was only formally described and named in 2018.

It was given the specific name japapigu, which means "Japan pig", because of its snout — instead of having the long, horse-like muzzle of other seahorses, this pygmy has a squished, piggy snout.

This seahorse is found in the coastal waters of southeastern Japan, but its range likely extends to the coasts of Taiwan and maybe China.

The maximum recorded length of a Japanese pygmy seahorse is 1.6 cm (0.63 in).

It clings to soft coral and algae with its prehensile tail, its paisley-patterned body appearing like an extension of the reef itself.

There are eight known species of pygmy seahorse.

The largest — Coleman’s pygmy seahorse — grows to a maximum length of 2.7 cm (1.1 in), while the smallest — Satomi’s pygmy seahorse — measures in at a max length of 1.4 cm (0.55 in).

Some of these pygmy species spend much of their lives clinging to corals, and their little bodies have adapted to mimic their hosts. Denise’s pygmy seahorse and Bargibant’s pygmy seahorse are adorable examples.

The first pygmy seahorse species to be discovered was Bargibant’s pygmy seahorse. It was found quite by accident in 1969 when Georges Bargibant stumbled upon it in the waters of New Caledonia while examining a gorgonian sea fan.

The most recently discovered species was the Sodwana pygmy seahorse — the first to be found in African waters — described in 2020.