Double-end Pipehorse, Syngnathoides biaculeatus (Bloch 1785)

Other Names: Alligator Pipefish, Double-ended Pipefish, Double-ended Pipe-fish, Double-ended Pipehorse, Spiraltail Pipefish

Double-end Pipehorses, Syngnathoides biaculeatus, in the Siam Centre, Bangkok, Thailand. Source: Erlend Bjørtvedt / Wikimedia Commons. License: CC BY Attribution-Noncommercial-ShareAlike 3.0


The Double-end Pipehorse, with its mottled green colour pattern is well-camouflaged to match its surroundings. This large pipefish uses its prehensile tail to cling to seagrasses and algae.

Identifying features:
Head in line with body axis, tail tip prehensile;
Body ridges flattened above, convex below without large spines;
Greenish, brownish or greyish with a mottled pattern.

Video of the birth of an Double-end Pipehorse (also known as an Alligator Pipefish)

Cite this page as:
Dianne J. Bray & Vanessa J. Thompson, Syngnathoides biaculeatus in Fishes of Australia, accessed 22 Jun 2024,

Double-end Pipehorse, Syngnathoides biaculeatus (Bloch 1785)

More Info


In Australian waters, known from Geraldton to Shark Bay, and north to Ashmore and Cartier Reefs, Western Australia, and from the Timor Sea, the Northern Territory, eastwards to Queensland and south to Batemans Bay (New South Wales). Elsewhere, widespread in the tropical Indo-West-Central Pacific from the Red Sea and East Africa, aross the Indian Ocean to Samoa and Tonga. 

Inhabits shallow, protected waters of bays, lagoons and estuaries including mangrove areas, in association with seagrass beds and macroalgae in depths at 0-10 m. Juveniles sometimes found clinging to floating algae and plant debris including Sargassum rafts.


Meristic features:
Dorsal-fin rays: 38-48
Anal-fin rays: 4
Pectoral-fin rays: 20-24
Trunk rings: 15-18
Tail rings: 40-54
Subdorsal rings 2.0–0.25 + 7.5–10.5 = 8.5–11.75

Body elongate, trunk compressed dorsoventrally, tail prehensile, tapering to a point, caudal fin absent; snout deep, laterally compressed, snout length 1.7–1.8 in head length, snout depth 5.3–7.8 in snout length; median dorsal snout ridge low, entire; a spine-like point usually on supraorbital ridge over posterior third of orbit; opercle without a longitudinal ridge; superior and inferior trunk ridges continuous with respective tail ridges; inferior trunk ridge inconspicuous and located ventrally on trunk; scutella absent; dermal flaps well developed in juveniles, often absent in adults.

Dorsal fin origin on trunk, fin base not elevated; pectoral fin base protruding laterally, usually with two distinct ridges; anal fin very small, caudal fin absent.


To 30 cm; males grow larger than females.


Colour variable depending on habitat - usually a mottled greenish-brown or grey with darker markings, sometimes with a narrow dark stripe on opercle and dots on abdomen. Subadult-adult females often with bilateral dark bluish spots or blotches ventrally on some trunk rings. Females may have a white zigzag pattern on abdomen.


Carnivore - feeds on small crustaceans such as shrimps and amphipods, and tiny fishes.  


Males brood the developing young in a specialized pouch under the trunk; pouch plates and folds absent. Males are likely to be brooding at 180 mm TL.

In Moreton Bay, Queensland, pregnant males were found between October and April, and pigment dots on the abdomen became very distinctive. Egg batches may develop sequentially in females, as ovaries contained at least two distinct egg size classes. Individuals are likely to be monogamous as males were found to be brooding embryos of a similar size.

Eggs are clear, white, brown or greenish in colour, and deposited in open membranous compartments on the abdomen. Males in Moreton Bay carried between 60 and 260 eggs per brood. (Takahashi et al. 2003).


Regularly collected for the aquarium trade, for use in traditional Chinese medicine and are sold as curios. They have been used in Chinese medicine to extract ‘Hailong’, a drug involved in cancer research. Individuals have also been reared in captivity. The species is harvested for sale in the Northern Territory aquarium industry.


  • EPBC Act 1999 : Marine Listed
  • IUCN Red List : Data Deficient
  • Remarks

    Uses its prehensile tail to cling to plants and if threatened, individuals have been observed to jump out of the water onto floating plant material.

    Similar Species


    Syngnathoides is from the Greek syn, symphysis (grown together) and gnathos (jaw). The specific name biaculeatus is from the Latin bi- (two, twice) and aculeatus (sharp-pointed, stinging) in reference to the spine-like points above the eye.

    Species Citation

    Syngnathus biaculeatus Bloch 1785, Naturgeschichte der ausländischen Fische 1: 10, Pl. 121 (figs. 1-2). Type locality: Indian Ocean.


    Dianne J. Bray & Vanessa J. Thompson

    Double-end Pipehorse, Syngnathoides biaculeatus (Bloch 1785)


    Allen, G.R. 1997. Marine Fishes of Tropical Australia and South-East Asia. Western Australian Museum, Perth.

    Allen, G.R. & M.V. Erdmann. 2012. Reef fishes of the East Indies. Perth, Australia: Universitiy of Hawai'i Press, Volumes I-III. Tropical Reef Research.

    Allen, G.R. & R. Swainston. 1988. The marine fishes of north-western Australia. A field guide for anglers and divers. Western Australian Museum, Perth. 201 pp.

    Bloch, M.E. 1785. Naturgeschichte der ausländischen Fische. Vol 1. Berlin, 136 pp.

    Dhanya, S., S. Rajagopal, S. Ajmal Khan & T. Balasubramanian. 2005. Embryonic development in alligator pipefish, Syngnathoides biaculeatus (Bloch, 1785). Current Science 88(1): 178–181.

    Dawson, C.E. 1985. Indo-Pacific Pipefishes (Red Sea to the Americas). Gulf Coast Research Laboratory, Ocean Springs, Mississippi. 230 pp.

    Dawson, C.E. 1986. Family No. 145: Syngnathidae (pp. 445–458). In: Smiths' Sea Fishes. Macmillan, South Africa. 1047 pp.

    Koldewey, H. 2005. Syngnathid Husbandry in Public Aquariums. Project Seahorse, Zoological Society of London and John G. Shedd Aquarium. (

    Kuiter, R.H. 1996. Guide to sea fishes of Australia. A comprehensive reference for divers and fishermen. New Holland, London, UK.

    Kuiter, R.H. 1997. Guide to sea fishes of Australia. A comprehensive reference for divers and fishermen. New Holland Publ., Frenchs Forest, NSW, Australia. 434 pp.

    Kuiter, R.H. 2009. Seahorses and their relatives. Aquatic Photographics, Seaford, Australia. Pp. 1–333.

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    Paxton, J.R., J.E. Gates, D.F. Hoese & D.J. Bray. 2006. Syngnathidae (Pp. 810–846). In  Hoese, D.F,. Bray, D.J., Paxton, J.R., Allen, G.R, Beesley, P.L. & Wells, A. (Eds) Zoological Catalogue of Australia. Volume 35. Fishes. ABRS & CSIRO Publishing, Australia., 3 vols.

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    Randall J.E., Allen G.R. & Steene R. 1997. Fishes of the Great Barrier Reef and Coral Sea. 2nd Edn. Crawford House Press, Bathurst. 557 pp.

    Shi, R., Y. Zhang & Z. Wang. 1993. Experimental studies on Hailong extracts from Syngnathoides biaculeatus. 1. The influences of Hailong extracts on human PBL proliferation and human tumour cell lines. Chin. J. Mar. Drugs/Zhongguo Haiyang Yaowu 12(2): 4–7.

    Takahashi, E., R.M. Connolly & S.Y. Lee. 2003. Growth and reproduction of double-ended pipefish, Syngnathoides biaculeatus, in Moreton Bay, Queensland, Australia. Environ. Biol. Fish. 67: 23–33.

    Quick Facts

    CAAB Code:37282100

    Behaviour:Prehensile tail

    Biology:Males brood eggs

    Conservation:IUCN Data Deficient; EPBC Act Marine Listed

    Depth:0-10 m

    Habitat:Seagrass & macroalgal beds

    Max Size:30 cm TL

    Species Image Gallery

    Species Maps

    CAAB distribution map