Pygmy Seahorse Species

How many species of pygmy seahorse are there?

Within the first decade of the 21st century seven new species of pygmy seahorse were officially named.  Before that, only Bargibant’s pygmy seahorse was known to science, having been described in 1970.  A few years ago, one species, Hippocampus severnsi, was synonymised with another, Pontoh’s (Hippoacmpus pontohi).  As of now, there are eight named species of pygmy seahorse, including the new Japanese Pygmy Seahorse, Hippocampus japapigu, and the Sodwana Pygmy Seahorse, Hippocampus nalu, which colleagues and I named, in August 2018 and May 2020 respectively.


My new book ‘The World Beneath‘ has a chapter about my pygmy seahorse research and the soap opera that is the lives of pygmies sharing a seafan together. MORE HERE

Bargibant’s Pygmy Seahorse (Hippocampus bargibanti) 1970. (Data Deficient)

Bargibant’s pygmy seahorse (Hippocampus bargibanti) was the first species of pygmy seahorse to be discovered.  In 1969 a New Caledonian scientist, Georges Bargibant, was collecting specimens of Muricella spp gorgonians for the Noumea museum and whilst one of these was on his dissection table he happened to notice a pair of tiny seahorses.  The next year they were officially named by Whitely as Bargibant’s pygmy seahorse.

Bargibant’s pygmy seahorses are found over the largest geographic range for a true pygmy seahorses, being found all the way from southern subtropical Japan, throughout the Philippines, Indonesia, east to Palau, Papua New Guinea, Solomon Islands, Fiji, Vanuatu and the Great Barrier Reef in Australia.

They are bigger only than Coleman’s pygmy seahorse (Hippocampus colemani), reaching a maximum total length of almost 2.7 cm.  They are also extreme habitat specialists, spending their entire adult life on a single gorgonian coral of the species Muricella paraplectana or M. plectana.

Probably due to their size and relative conspicuousness compared to other pygmy seahorses, they are one of the most commonly observed by SCUBA divers.  Great care must be taken when viewing and photographing any marine life but these diminutive seahorses are particularly susceptible to damage from poor diving and photographic techniques.  It is vital that neither the seahorses nor their gorgonian host are touched in any way and bright constant lights such as flash lights/torches have been shown to disturb the seahorse’s natural behaviours.

Denise’s Pygmy Seahorse (Hippocampus denise) 2003. (Data Deficient)

Denise’s pygmy seahorse (Hippocampus denise) is a highly variable species, which like its close relative Bargibant’s pygmy seahorse, is a habitat specialist living in an obligate relationship with gorgonian corals.  However, unlike Bargibant’s, Denise’s pygmy seahorse is a relative generalist is terms of the number of host species it inhabits.  During my PhD study on these species’ biology I recorded H. denise from a total of ten gorgonian genera (including: Acanthogorgia sp, Annella sp, Echinogorgia sp, Ellisella sp, Melithaea sp, Muricella sp, Verrucella sp, Villogorgia sp), compared to just one for H. bargibanti.  Once settled on a gorgonian following some time floating in the plankton as a juvenile, the small seahorse settles, at around 1.3 cm in length, to a host where it remains for the rest of its life. Once fully-grown they reach a maximum length of 2.4 cm.

During my PhD research I was lucky enough to observe Denise’s pygmy seahorse mating, fighting and even giving birth on numerous occasions.  The young settle to a host and over a few days take on its exact colouration.  This results in a wide range of colours and skin textures in this species with some individuals being smooth and others bumpy, depending on their host polyp’s prominence.

The habitat specificity for the gorgonian-associated pygmy seahorses, H. denise and H. bargibanti, puts them at a higher risk of extinction than non-specialist species.  Gorgonians can live for 100 years but can easily be damaged by natural phenomena such as storms, but also human induced threats such as diver damage, anchor damage, destructive fishing practices and even climate change.  Denise’s pygmy seahorse is found living on the lush coral reefs of southeast Asia, from Borneo to New Guinea, Solomon Islands and Palau.  This region is also sadly under the greatest threat from human damage.  The best method for protecting these tiny fish is within Marine Protected Areas (MPAs) and by careful regulation of diver interactions so the seahorses are not accidentally damaged by interested divers.

Pontoh’s Pygmy Seahorse (Hippocampus pontohi) 2008. (Least Concern)

Pontoh’s pygmy seahorse (Hippocampus pontohi) was one of three species officially named in 2008.  These three species are free-living, rather than associated with gorgonian corals like Bargibant’s and Denise’s pygmy seahorses.  They are much smaller in size, reaching just under 1.7 cm in length from the tip of the tail to the snout.  Although Pontoh’s pygmy seahorse can be found anywhere on tropical reefs within their range, they are most commonly found living in pairs or small groups in clumps of the calcareous alga, Halimeda or on hydroids.  They are found within the Coral Triangle area that includes Indonesia, Papua New Guinea, Solomon Islands and also Fiji.  They are often found in shallower areas than the gorgonian-associated species between 3 – 20 m. 

When they were initially described, Severn’s pygmy seahorse was considered to be distinct despite being morphologically identical. Basically, brown free-living pygmies were considered Severn’s (Hippocampus severnsi) and white ones Pontoh’s.  In 2016 they were officially synonymised and the name Severn’s was dropped.

Satomi’s Pygmy Seahorse (Hippocampus satomiae) 2008. (Data Deficient)

Satomi’s pygmy seahorse (Hippocampus satomiae) is one of the hardest species to find, let alone photograph.  Not only is it the world’s smallest seahorse, reaching a maximum total length of less than 1.4 cm but it is nocturnal and very active.  I was shown a group of these tiny fish by my friend Yann Alfian in Raja Ampat, West Papua.  I used a very small, dull focus light with a red filter to observe these diminutive seahorses to reduce any disturbance to them.  They were more active than any other pygmy species I’ve observed.

They were scientifically described in 2008 and are known only from a few localities in Indonesia.  Their small size and nocturnal habits probably mean they are more widely distributed than this but have just evaded detection.  Satomi’s pygmy seahorses were originally found by Satomi Onishi (hence the scientific name) off Derawan Island in Indonesian Borneo.  There is very little scientific information on Hippocampus satomiae but their classification like other seahorses places them in the Syngnathid subfamily Hippocampinae and as fishes they are within the phylum chordata.  The habitat preferred by Satomi’s pygmy seahorses is rich coral walls, I saw them under overhangs with diverse soft coral growth at a depth of 18 m.

Satomi’s pygmy seahorse can be identified by their small size, a small black dot between the eye and the snout as well as orange filaments and markings on the back, tail and chin.

Walea Soft Coral Pygmy Seahorse (Hippocampus waleananus) 2009. Not yet listed

One of my favourite pygmy seahorses, and one I was lucky enough to see at the now closed Walea Resort in the Togian Islands of central Sulawesi, Indonesia, is the Walea Soft Coral pygmy seahorse (Hippocampus waleananus).  This is another species that lives in association with a sessile invertebrate, in this case soft corals of the genus Nephthea.  The stems of soft corals are much more variable and larger in diameter than gorgonian stems and as a result the tail of Walea pygmy seahorses are significantly longer than those of other pygmy seahorses.

This pygmy seahorse is unique in being restricted to only a very small geographic area.  It lives only in the Tomini Gulf of central Sulawesi, Indonesia and nowhere else on the planet.  As a result the threats faced by this species are magnified compared to the other pygmy seahorses.  As an extreme habitat specialist its existence also relies entirely on the soft corals that it inhabits. Like many scleractinian corals, these soft corals contain zooxanthellae in their cells and can ‘bleach’ as a result of climate change and warming ocean waters.  If these corals disappear from the small gulf, so too does the Walea pygmy seahorse.

Coleman’s pygmy seahorse (Hippocampus colemani) 2003. (Data Deficient)

Coleman’s pygmy seahorse is a bit of an enigma, it is thought to be restricted to Lord Howe Island off the east coast of Australia although there are unconfirmed reports from eastern Papua New Guinea and Taiwan.  I am yet to observe this species in the wild.

Japanese pygmy seahorse (Hippocampus japapigu) 2018. Not yet listed

I described the Japanese pygmy seahorse, Hippocampus japapigu, (known locally as 日本のピグミータツノオトシゴ or Japapigu) in 2018, based on field work I conducted in 2013. It is found, as the name suggests, in Japan.  They are not found living in close association with a specific host such as a gorgonian or soft coral, rather they cling to algal turfs in the subtropical reefs on which they live.

The species is characterised, and distinguished from the other free-living pygmies, by a reticulate pattern of white lattice over the body, which often has a black spot within it.  There are also several morphological and genetic differences between this and other pygmy seahorses.  The body colouration is brown, beige, to pink and whitish.

They inhabit subtropical and temperate reefs from southern to the central west of Japan.  The Izu islands of Miyake and Hachijo are good locations to find these elusive seahorses, as well as Kushimoto and Sagami Bay.  I have seen many in the 8-15 metre range in protected areas, where they were living amongst the algal turf and small hydroids.

Beyond my work in naming this species in 2018, there is very little known about their biology or conservation.  This is true of all the free-living pygmy seahorses, which are yet to receive a research focus.  My PhD work on the gorgonian-associated pygmy seahorses is the only research on these species’ biology yet to be carried out.

– Along with some colleagues, I published the scientific description (formal naming) of this species in August 2018:

Short G, Smith R, Motomura H, Harasti D, Hamilton H (2018) Hippocampus japapigu, a new species of pygmy seahorse from Japan, with a redescription of H. pontohi (Teleostei, Syngnathidae). ZooKeys 779: 27-49.

Sodwana pygmy seahorse (Hippocampus nalu) 2020. Not yet listed

In 2020, I described the Sodwana, or South African, Pygmy Seahorse with colleagues Graham Short and Dr Louw Claassens.

Hippocampus nalu – South African pygmy seahorse, Sodwana Bay