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Lowcrown Seahorse Hippocampus dahli Ogilby, 1908
[CAAB 37 282114]

Distribution Map see an interactive map here (new window)

Until recently, the Lowcrown Seahorse, found in north and north-eastern Australia, was thought to be a synonym of the Flatface Seahorse, Hippocampus planifrons, which lives in north Western Australia.

Distribution, ecology and habitat:

Endemic tropical north and north-eastern Australian species, from Darwin, NT to Moreton Bay, Qld; benthic, in inshore waters on soft bottoms or rubble substrates or in estuarine channels to 21 m.

Size:

Height to about 120 mm.

Food and feeding:

Carnivores. Like most other seahorses, this species presumably feeds by sucking crustaceans and other small prey items, including planktonic zooplankton, into its mouth.

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.
Eggs: Not described.
Larvae: Not described.

Characteristics:

Meristics: D 21-22 (usually 21); A 4; P 17-18 (usually 17); trunk rings 11; tail rings 37-40 (usually 39); subdorsal rings 4 (2-3 + 1-2).
Head and body: Body long, slender and thin, flattened and relatively smooth; head narrow; snout long, about half head length.
Spines and tubercles: Body relatively smooth, spines reduced and low; nasal spine absent; lateral head spine as a low tubercle; shoulder-ring spine single, recurved; subdorsal 3/0,1,1 or 4/0,0,1,1; body tubercles small to moderate along dorsal and lateral ridges, somewhat enlarged along dorsal-fin base.
Coronet: Coronet very low, laterally flattened, front and lateral edges rugose, posterior edge with 3 short backward directed spines.
Lateral line: Lateral line visible as a small pore just above the lateral trunk ridge on each spine to 19^th-23^rd tail ring, then intermittent.

Colour:

Colour pattern sexually dimorphic. In life - females mostly pale brown to almost black, usually with small black scribble marks sometimes forming lined, zebra-like patterns. Males usually dark brown to almost black with black scribbles. In preservative - similar to live coloration, but somewhat darker.

Similar species:

Similar to H. planifrons, from which it differs in having a very low coronet, poorly-developed spines on the trunk and tail ridges, an upward-directed nape spine and in lacking spots laterally on the snout.

Fisheries:

Specimens are caught and discarded as bycatch by the prawn trawl fishery. There is no known trade for the Lowcrown Seahorse, however, since the 1960's, the species has declined significantly in parts of Moreton Bay, Qld, possibly due to habitat degradation and commercial trawling.

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/.
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:

Until recently, H. dahli was thought to by a synonym of H. planifrons. Minor differences between individuals of H. dahli from the southern and northern parts of its distribution range are thought to represent clinal variation.

Other common names:

Low-crown Seahorse

Original citation:

Hippocampus dahli Ogilby 1908, Ann. Qld Mus. 9(1): 17, Noosa, Queensland.

Etymology:

From the Greek ippos = horse and kampe = curvature. The specific name dahli is after Knut Dahl a Norwegian naturalist, author of In Savage Australia, published in 1926.

References:

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.

Horne, M.L. 2001. A new seahorse species (Syngnathidae: Hippocampus) from the Great Barrier Reef. Rec. Aust. Mus. 53: 243-246.

Johnson, J.W. 1999. Annotated checklist of the fishes of Moreton Bay, Queensland, Australia. Mem. Qld Mus. 43(2): 709-762 [as Hippocampus planifrons]

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.

Ogilby, J.D. 1908. New or little known fishes in the Queensland Museum. Ann. Queensl. Mus. 9(1): 1-41.

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.

Whitley, G.P. 1952. Some noteworthy fishes from eastern Australia. Proc. Roy. Soc. N. S. W. 1950/51: 27-32.

Whitley, G.P. & J. Allan. 1958. The sea-horse and its relatives. The Griffin Press, Adelaide, Australia.