Southern Pygmy Leatherjacket, Brachaluteres jacksonianus (Quoy & Gaimard, 1824)

Introduction

The Southern Pygmy Leatherjacket is small member of the Monacanthidae family. Its Latin name is derived as follows:

brachys - short (Greek)
aluteres - refers to another genus of monacanthid: Aluterus
jackson - named after Port Jackson (Sydney Harbour)
ianus - pertaining to, belonging to (Latin)

Presumably the genus name was chosen to describe the shape and common colouration of this species. The species name refers to Port Jackson (Sydney Harbour), the place where the fish used in the description of the species was caught.

Identification

The Southern Pygmy Leatherjacket has a very compressed body, which is almost circular. The lower surface is made up of a large ventral flap (called a dewlap) which can be raised and lowered. The abdomen is also expandable by inflating. Like all the leatherjackets, the Southern Pygmy Leatherjacket lacks pelvic fins. Instead, they all have a shaft-like pelvic bone, the end of which is covered with specialised scales.

The colouration of the Southern Pygmy Leatherjacket is highly variable, ranging from a pale yellow-brown to dark green with small spots or ocelli. This variable colouration helps to camouflage the fish and often makes it very difficult to see. The colouration of this fish can change during courtship.

Habitat

The Southern Pygmy Leatherjacket can be found in a range of habitats including shallow seagrass beds and areas of kelp in coastal bays.

Distribution

The Southern Pygmy Leatherjacket is endemic to Australia occurring in temperate coastal waters from southern Queensland to south-western Western Australia and south around Tasmania.

Fishes in the genus Brachaluteres occur in tropical marine waters of the Western Pacific. The genus contains four species, two of which are known from Australia, the Southern Pygmy Leatherjacket and Taylor's Pygmy Leatherjacket, Brachaluteres tayloriwhich is recorded in tropical waters from northern to southern Queensland.

The map below shows the Australian distribution of the species based on public sightings and specimens in Australian Museums. Click on the map for detailed information. Source: Atlas of Living Australia.

Other behaviours and adaptations

The Southern Pygmy Leatherjacket is not a strong swimmer. It has small pectoral fins, a large rounded caudal fin and long-based dorsal and anal fins. The species avoids predators by hiding in seagrass and kelp beds.

It may not be fast but it is very manouverable. When moving slowly between blades of seagrass or fronds of kelp, it swims by undulations of the opposing dorsal and anal fins. When swimming at higher speed, for example when avoiding a predator, the fish beats the caudal fin.

References

1. Gomon, M.F., Bray, D. & R.H. Kuiter (Eds). 2008. The Fishes of Australia's Southern Coast. Reed New Holland. Pp. 928.
2. Hutchins, B. & R. Swainston. 1986. Sea Fishes of Southern Australia. Complete Field Guide for Anglers and Divers. Swainston Publishing. Pp. 180.
3. Hutchins, B. & M. Thompson. 1983. The Marine and Estuarine Fishes of South-western Australia. Western Australian Museum. Pp. 103.
4. Kuiter, R.H. 2000. Coastal Fishes of South-eastern Australia. Gary Allen. Pp. 437.
5. Last, P.R., Scott, E.O.G. & F.H. Talbot. 1983. Fishes of Tasmania. Tasmanian Fisheries Development Authority. Pp. 563.