Marine life  /  Seahorses & pipefish  /  Thorny seahorse
Reviewed 2026-09-04
Species entry

Thorny seahorse

Hippocampus histrix

A full-sized seahorse of silt and sponge, with long sharp spines.

Size
To 17 cm
Depth
5–25 m
Habitat
Silt, sponge and debris
Active
Daylight
Range
Indo-Pacific
Rarity
Lembeh Strait
3 stars of 5, a good week should turn one up
Thorny seahorse, Hippocampus histrix
Simon Buxton

Not a pygmy: a full-sized seahorse of 15 to 17 cm, slender and elongate, carrying long, sharp, dark-tipped spines of fairly even length, with four or five more on the coronet and further spines over the forehead, cheeks, nose and eyes. The snout is very long and tapered and usually carries one or more fine white lines along it, which together with the long even spines is the signature. Colour is no use — grey, cream, bright yellow, green, red or brown, plain or patterned. The confusion is with Hippocampus spinosissimus, which has shorter, blunter, unequal spines and a shorter snout.

Sponges, weedy rocky reef, soft corals and seagrass, and on muck also on plain rubble and sand. The male broods in a pouch on the tail; the species is reported to form pairs. It takes zooplankton and small crustaceans. Recorded from the surface to 82 m though usually between 15 and 40, right across the Indo-Pacific from South Africa to French Polynesia, and absent from the Red Sea. This is one of the few animals on this site with a real conservation problem attached: it is listed as Vulnerable, with populations thought to have fallen by more than thirty per cent over a decade and a half, under pressure from the dried-seahorse trade and the aquarium trade rather than from diving.

Where to find:

LocationRarity Best monthsDepthHabitat
Lembeh Strait Indonesia editorial estimate
3 stars of 5, a good week should turn one up
Year-round
5–25 m
Silt, sponge and debris
Dauin & Dumaguete Philippines editorial estimate
3 stars of 5, a good week should turn one up
Year-round
5–20 m
Silt

Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.

Related species

SP
alligator pipefish
16:10
Alligator pipefish
Syngnathoides biaculeatus
SP
atlantic banded pipefish
16:10
Atlantic banded pipefish
Micrognathus crinitus
SP
banded pipefish
16:10
Banded pipefish
Dunckerocampus dactyliophorus
SP
barbour's seahorse
16:10
Barbour's seahorse
Hippocampus barbouri