Thorny Seahorse, Hippocampus histrix Kaup 1856

A Thorny Seahorse, Hippocampus histrix, at The Pipeline, Nelson Bay, New South Wales, depth 8 m. Source: Dave Harasti / License: All rights reserved


This distinctive seahorse with long dark-tipped spines, and a variable colour pattern to match the surroundings, ranging from cream to grey, greenish, yellow or brown to burgundy-red, sometimes with saddle-like markings and small darker spots and blotches. 

Cite this page as:
Bray, D.J. 2020, Hippocampus histrix in Fishes of Australia, accessed 04 Dec 2022,

Thorny Seahorse, Hippocampus histrix Kaup 1856

More Info


Recorded in Australia from south of Ashmore Reef, Timor Sea, the Great Barrier Reef, Queensland, and in Port Stephens, New South Wales. Elsewhere the species occurs in the tropical and subtropical Western Pacific, from Bali, Indonesia, Papua New Guinea, New Caledonia and Japan. 

Inhabits areas with both hard and soft bottoms, often attached to soft corals or sponges at 10-95 m, usually below 15 m. The Thorny Seahorse may also be found on shallower algae-rubble or rocky reef areas in about 10 m.


Meristic features: Dorsal fin 17-19; Anal fin 4; Pectoral fin 17-18; trunk rings 11; tail rings 33-34; subdorsal rings 2 + 1. 

Head long, about equal to trunk length, angled down to near trunk; snout long, equal to or longer than head length; body narrow; dorsal fin short-based.

Spines very elongate, extremely sharp; nape spine immediately before coronet, elongate and directed upwards, slightly longer than spine above eye; lower shoulder-ring spine elongate, single, directed laterally and slightly forward; spine above eye about equal to eye diameter; nose spine slightly longer than spine above eye; cheek spine single; 2 sharp neck spines, similar to coronet spines in length; trunk ridge spines on nearly all trunk and tail junctions, only absent on 1st ring of lateral ridge, starting on 4th; subdorsal spines 3/0,1,0.

Coronet of moderate height, large, with 5 elongate divergent spines on apex.


Height to 150 mm.


Base colour highly variable to match surroundings, from cream to grey, greenish, yellow or brown to burgundy-red; body plain or with saddle-like markings, often with small darker spots and blotches on sides and dorsal surface; small areas with tiny reddish spots on nape and dorsal surface; snout usually with one to several fine white bars; tips of spines often black.


Like other seahorses, this species presumably preys on small crustaceans and other planktonic organisms.


The female uses an ovipositor to transfer her eggs into an elaborate enclosed pouch under the abdomen of the male. The male not only fertilizes the eggs inside the pouch and provides physical protection for the developing embryos, he also osmoregulates and aerates the embryos and may provide some nourishment until the offfspring are born.


Rarely collected for the aquarium trade due to its preferred habitat in moderately deeper waters. Specimens may be dried and sold in the traditional medicine trade or as curios.


Listed under Appendix II of the Convention on the International Trade in Endangered Species of Wild Flora and Fauna (CITES). As a result, the species is subject to the Convention at H. histrix is listed as Data Deficient by IUCN.


The name H. histrix has often been used for many spiny seahorses inhabiting tropical regions, giving the impression that these spiny species are widespread rather than having relatively restricted distributions.

Similar Species

H. histrix is most often confused with H. multispinus, from which it differs in having a single long shoulder-ring spine rather than the long double lower shoulder-ring spines of H. multispinus that diverge from one another in a V-shape. In addition, the nape spine is close to the coronet and is directed upwards in H. histrix, whereas it is removed from the coronet and directed forwards in H. multispinus.

Species Citation

Hippocampus histrix Kaup 1856, Cat. Lophobranchiate Fish: 17, Pl. 2 (fig. 5), Japan.


Bray, D.J. 2020

Thorny Seahorse, Hippocampus histrix Kaup 1856


Harasti, D. 2015. Range extension and first occurrence of the thorny seahorse Hippocampus histrix in New South Wales, Australia. Marine Biodiversity Records 8: e49

Kaup, J.J. 1856. Catalogue of lophobranchiate fish in the collection of the British Museum. London: 1-76, Pls. 1-4.

Kuiter, R.H. 2000. Seahorses, Pipefishes and their Relatives. Chorleywood, UK: TMC Publishing, 240 pp.

Kuiter, R.H. 2001. Revision of the Australian Seahorse of the genus Hippocampus (Syngnathiformes: Syngnathidae) with descriptions of nine new species. Rec. Aust. Mus. 53: 293-340.

Kuiter R.H. 2009. Seahorses and their relatives. Seaford: Aquatic Photographics 

Lourie, S.A., S.J. Foster, E.W.T. Cooper & A.C.J. Vincent. 2004. A guide to the dentification of seahorses. University of British Columbia and World Wildlife Fund, Washington D.C.

Nakabo, T. (ed.) 2002. Fishes of Japan with pictorial keys to the species. Tokai University Press. Fish. Japan Pict. Keys Species v. 1: i-lxi + 1-866.

Quick Facts

CAAB Code:37282134

Biology:Males brood the eggs

Conservation:IUCN Data Deficient; CITES Listed

Depth:5-95 m

Habitat:Reef associated

Max Size:Height 15 cm

Species Image Gallery

Species Maps

CAAB distribution map