Lowcrown Seahorse, Hippocampus dahli Ogilby 1908

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.

Dorsal fin 21-22 (usually 21); Anal fin 4; Pectoral fin 17-18 (usually 17); trunk rings 11; tail rings 37-40 (usually 39); subdorsal rings 4 (2-3 + 1-2).
Body long, slender and thin, flattened and relatively smooth; head narrow; snout long, about half head length.
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 very low, laterally flattened, front and lateral edges rugose, posterior edge with 3 short backward directed spines.
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 pattern is 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.

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

Sexes are separate. 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.

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.

EPBC Act 1999: Marine Listed under the Federal Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act 1999). http://www.environment.gov.au/epbc/species/marine.html

Until recently, H. dahli was thought to by a synonym of H. planifrons.

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.

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.

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

Dianne J. Bray