Bigbelly Seahorse, Hippocampus abdominalis Lesson 1827

Other Names: Big-bellied Sea-horse, Big-belly Seahorse, Eastern Potbelly Seahorse, Pot-bellied Seahorse, Potbelly Seahorse

A male Bigbelly Seahorse, Hippocampus abdominalis, in Port Phillip, Victoria, May 2013. Source: Julian K. Finn / Museum Victoria. License: CC by Attribution-NonCommercial


The Bigbelly Seahorse is the largest seahorse in Australia. It has a low triangular coronet, low, rounded bumps above the eyes, and fleshy filaments off the head. Adult males have a very prominent abdomen, whereas females have a compressed abdomen with a keel down the middle.

Individuals range in colour from almost white to a mottled yellow, reddish or even brown, with irregular darker spots and blotches, and a broadly banded tail. They are often seen clinging to sponges and macroalgae.

Bigbelly Seahorse view of the annual spider crab migration in Port Phillip Bay, Victoria.

Cite this page as:
Bray, D.J. & Thompson, V.J. 2018, Hippocampus abdominalis in Fishes of Australia, accessed 13 Jul 2024,

Bigbelly Seahorse, Hippocampus abdominalis Lesson 1827

More Info


Known from temperate waters of New Zealand and southern Australia, where it occurs from about South West Rocks, New South Wales, southwards to the northern Great Australian Bight, South Australia, and south to the Derwent Estuary, Tasmania. 

Bigbelly seahorses live in a range of habitats from intertidal rockpools, low rocky reefs in shallow estuaries, to deep tidal channels and deeper coastal reefs to 100m. They cling to seagrasses, sponges, macroalgae such as kelp holdfasts, rocky outcrops and man-made structure. Individuals have also been found clinging to floating seagrass rafts.


Dorsal fin 25-33; Anal fin 4; Pectoral fin 14-16; trunk rings 12-13; tail rings 44-48; subdorsal rings 3-5 + 1-2; Rings supporting dorsal fin 4 trunk and one tail ring

Body slender, elongate, tail prehensile. Trunk of moderate depth to deep, distended ventrally in adult females. Head small, at right angles to body, snout moderately long, dorsal-fin base moderately long.

Body spines becoming progressively smaller with growth. Pelagic young have angular spines of moderate length along trunk and anterior tail ridges, remaining as rugose tubercles in large adults. Tubercles enlarged above eyes, on trunk mainly below the dorsal fin, and along shoulder ring at gill-opening with one of moderate size ventrally.

The coronet is very low and somewhat triangular, with a rugose ridges and 2 blunt spines posteriorly in some adult specimens.

The lateral line is visible as small indistinct pores with low papillae, usually only detectable intermittently, reaching posteriorly to about 30th tail ring. Adults usually have long dermal filaments on various head spines.


This species is the largest known seahorse, reaching 35 cm TL (total length), and 23 cm in height.


The colour is variable, ranging from overall whitish, grey, yellow, orange, purplish to brown, usually with paler sides and a variable number of black spots on the head and trunk. 

Individuals living in shallow bays are usually brownish with many dark spots, whilst those in deep waters tend to be plain with brighter colours similar to the sponges on which they live. The tail may have indistinct banding.


Feed by sucking small invertebrates in through their tubular snouts - especially carid and mysid shrimps, and amphipods.


Bigbelly seahorses breed year-round, with a peak during the warmer months. As with other seahorses, this species exhibits elaborate courtship behaviour. A female may attract a number of males which compete for the chance to brood her eggs. They brighten their pouches, and pump them repeatedly by inflating and emptying them to entice her to deposit her eggs inside.

Although males and females do not form monogamous pairs and promiscuous courtship behaviour has been observed, genetic studies examining male broods in several Tasmanian populations showed that the males were carrying a single brood. Males, however, may switch mates between broods.

Spawning occurs from October to January and females use an ovipositor to transfer the eggs into an elaborate enclosed pouch under the abdomen of the male. The male fertilizes the eggs inside his pouch and provides physical protection for the developing embryos. He also osmoregulates and aerates the embryos and may provide some nourishment until his offspring are born. Larvae are born after a gestation period of about 4 weeks.

Males brood between 300 to about 700 eggs per brood. During summer, males incubate up to 4 broods. One male seahorse in the aquaculture industry reportedly produced a brood of 1116 young.

The larvae are morphologically similar to adults and are born after a gestation period of about one month. Newly born larvae are slender, 15-21 mm in length, with a relatively straight body at birth, bending to adult form within 1-2 days. They have angular spines of moderate length along the trunk and anterior tail ridges, and the spines diminish in size in post-pelagic young. 

Larvae rise to surface immediately after emerging from the pouch and cling to to each other and floating debris with their prehensile tail. Juveniles settle to the bottom at around 20-30 mm.

Bigbelly seahorses are easily kept in aquaria if fed regularly on live diet of small shrimp and other crustaceans, especially mysids.


Occasionally taken as bycatch in commercial trawls. Captive-bred specimens are reared commercially in a number of Australian States and live individuals are collected as broodstock for aquaculture operations. 

Both wild caught and aquarium-reared individuals are sold within Australia and exported overseas for the live aquarium trade. 

Dried specimens are sold in Asia in the Traditional Medicine industry.


CITES: Listed under Appendix II of the Convention on the International Trade in Endangered Species of Wild Flora and Fauna (CITES).
Listed as Data Deficient on the 2008 IUCN Red List of Threatened species.

EPBC Act 1999: Marine Listed under the Federal Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act 1999).


Contention exists as to whether the east coast populations of H. abdominalis differ from those found in southern waters. Although Kuiter (2004) referred to the southern populations as Hippocampus bleekeri, genetic studies found little evidence to support this hypothesis (Armstrong 2001).

Similar Species

The Bigbelly Seahorse has a deeper trunk, more tail rings and more dorsal-fin rays that other seahorse species.


Hippocampus is from the Greek, ippos = horse and kampe = curvature. The specific name abdominalis refers to the enlarged and prominent abdomen.

Species Citation

Hippocampus abdominalis Lesson 1827, Bull. Sci. nat Férussac 12: 127, New Zealand.


Bray, D.J. & Thompson, V.J. 2018


Australian Faunal Directory

Bigbelly Seahorse, Hippocampus abdominalis Lesson 1827


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Quick Facts

CAAB Code:37282120

Biology:Males brood eggs

Conservation:EPBC Act: Marine listed

Conservation:IUCN Least Concern; CITES Listed

Depth:0-100 m

Max Size:35 cm TL

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CAAB distribution map