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West Australian Seahorse Hippocampus subelongatus Castelnau, 1873
[CAAB 37 282123]

Distribution Map see an interactive map here (new window)

In early summer, the West Australian Seahorse congregates in the lower reaches of the Swan River and is collected for the live aquarium trade.

Distribution, ecology and habitat:

Endemic to subtropical and temperate waters of Western Australia, from about Cockburn Sound to Kalbarri; benthic in sheltered bays, inhabiting algal and sponge reefs, jetty pylons and moorings at 1-25 m.

Size:

Height to 200 mm.

Food and feeding:

Individuals congregate in the lower reaches of the Swan River during early summer when many crustaceans are spawning, providing food for their offspring. Feed diurnally sucking up small crustaceans and passing zooplankton.

Reproduction and early life history:

Reproduction: Sexes separate, reproduction a form of viviparity or ovoviviparity, whereby the males give birth to tiny independent young. 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. The gestation period usually lasts 2-3 weeks, varying with water temperature. Genetic studies of maternity in male broods have shown that male H. elongatus receive eggs from only one female for each particular brood, and that some male/female pairs remain monogamous during the breeding season.
Eggs: Brood size up to 720 eggs.
Larvae: Morphologically similar to adults at birth.

Characteristics:

Meristics: D 18; P 17-18; trunk rings 11; tail rings 33-34; subdorsal rings 2 + 1.
Head and body: Body slender in both sexes, head long, about 85-90% trunk length, snout long and narrow, about half head length; rings thick.
Spines and tubercles: Subdorsal spines 3/0,1,0-0.5. Spines on trunk and tail of moderate length in juveniles, becoming blunt with growth and appearing as low tubercles in adults. Nasal spine angular; enlarged tubercles above eyes, laterally on head, and sub-dorsally on trunk; nape spine long when young; shoulder-ring with 3 blunt spines, uppermost just above top of pectoral-fin base, central spine at level of last few rays of pectoral-fin base and lowermost double, in form of short laterally-directed, divergent spines.
Coronet: Coronet tall, crown with 5 spines in star-like arrangement when young, spines becoming blunt and forming rounded flanges in large adults.
Lateral line: Lateral line indistinct, pores extending to 22^nd tail ring.

Colour:

In life, colour highly variable from grey, yellow, brown to burgundy-red, usually with thin dark barring on snout; body plain or with dusky striations or reticulations; dorsal surface of trunk edged with a dark vertical line. In preservative - overall pale brown, otherwise patterns similar to those of live individuals.

Similar species:

H. subelongatus is most similar to H. angustus, with which it has been confused. H. angustus has a lower coronet with distinct spines, spines on body ridges junctions and occurs northwards from Shark Bay.

Fisheries:

Both wild caught and captive bred H. subelongatus are sold in Australia and exported for the aquarium trade. Reported population declines in the Swan River may be a result of over-collecting, or may be due to seasonal environmental fluctuations.

Conservation Status:

International: 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, http://www.cites.org/.
Listed as Data Deficient on the 2007 IUCN Red List of Threatened species. http://www.iucnredlist.org/search/details.php/40773/summ
Australian legislation: Marine Listed under the Federal Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act 1999). http://www.environment.gov.au/epbc/species/marine.html

Remarks:

H. subelongatus occurs seasonally in the lower reaches of the Swan River, moving to deeper waters in winter.

Other common names:

Tigersnout Seahorse.

Original citation:

Hippocampus elongatus Castelnau 1873, Proc. Zool. Acclim. Soc. Vict. 2: 144, Fremantle, Western Australia.

Etymology:

From the Greek ippos = horse and kampe = curvature. The specific name subelongatus is from the Latin sub- meaning less than and elongatus meaning prolonged, in reference the moderate spine length of this species.

References:

Castelnau, F.L. 1873. Contribution to the ichthyology of Australia. Nos. III thru IX. Proc. Zool. Acclim. Soc. Victoria 2: 37-158.

Hoese, D.F., D.J. Bray, J.R. Paxton & G.R. Allen. 2006. Fishes. In Beesley, P.L. & A. Wells. (eds.) Zoological catalogue of Australia. Volume 35. ABRS & CSIRO Publishing: Australia, 2178 pp.

Jones, A.G., C. Kvarnemo, G.I. Moore, L.W. Simmons & J.C. Avise. 1998. Microsatellite evidence for monogamy and sexbiased recombination in the Western Australian seahorse Hippocampus angustus. Mol. Ecol. 7: 1497-1506.

Kvarnemo, C., G.I. Moore, A.G. Jones, W.S. Nelson & J.C. Avise. 2000. Monogamous pair bonds and mate switching in the Western Australian seahorse Hippocampus subelongatus. J. Evol. Biol. 13: 882-888.

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

Lourie, S.A., A.C.J. Vincent & H.J. Hall. 1999. Seahorses: an identification guide to the world's species and their conservation. Project Seahorse. London, UK, 214 pp.

Martin-Smith, K.M. & A.C.J. Vincent. 2006. Exploitation and trade of Australian seahorses, pipehorses, sea dragons and pipefishes (Family Syngnathidae). Oryx, 40(2): 141-151.

Payne, M.F. & R.J. Rippingale. 2000. Rearing West Australian seahorse, Hippocampus subelongatus, juveniles on copepod nauplii and enriched Artemia. Aquaculture 188: 353-361.

Pogonoski, J.J., D.A. Pollard & J.R. Paxton. 2002. Conservation Overview and Action Plan for Australian Threatened and Potentially Threatened Marine and Estuarine Fishes. Canberra, Environment Australia, 375 pp.

Wilson, A.B, I. Ahnesjo, A.C.J. Vincent & A. Meyer. 2003. The dynamics of male brooding, mating patterns, and sex roles in pipefishes and seahorses (family syngnathidae). Evolution 57(6): 1374-1386.