Rusty Flathead, Inegocia japonica (Tilesius 1812)

Other Names: Japanese Flathead, Lizard Flathead

Summary:

A smallish orange to brown flathead, with a flecked or mottled pattern, a pale underside, and many dark spots of varying sizes on the tail.

Cite this page as:

CSIRO Marine & Atmospheric Research & Bray, D.J. 2017, Inegocia japonica in Fishes of Australia, accessed 15 Apr 2025, https://fishesofaustralia.net.au/home/species/2179

Rusty Flathead, Inegocia japonica (Tilesius 1812)

More Info

Distribution	Continental shelf of northern Australia from Moreton Bay, Queensland, to the Northwest Shelf and possibly to Cockburn Sound, Western Australia. Elsewhere the species is widespread in the Indo-west Pacific, including Papua New Guinea, Indonesia, Philippines, southern Japan, South China Sea, Gulf of Thailand to India and Sri Lanka. Demersal in bays and coastal waters to depths between 5-85 m.
Features	Dorsal fin IX or I,VIII, 11-13 (usually 12); Anal fin 11-13 (usually 12); Pectoral fin 19-21 (usually 19 or 20); Pelvic fin I, 5; Lateral line scales (pored) 51-55 (usually 52 or 53). Body elongate, moderately depressed. Head large (length ~34-35% SL), moderately depressed, supraorbital ridge smooth anteriorly, with serrations over posterior half of eye; preorbital spine absent; a single preocular spine; suborbital ridge usually smooth except for 2 spines under eye (specimens from Indonesia and Australia frequently have a few additional small serrations); Lower side of head bicarinate; ocular flap absent; teeth on jaws low and fine, teeth on vomer in two parallel longitudinal patches; preopercular spines usually 3, upper preopercular spine short, subequal with next; small accessory spine usually present; interopercular flap elongate, pointed; Total gill rakers on first arch 5-7 (usually 6). Scales small, finely ctenoid dorsally, cycloid ventrally, covering body and most of head behind eyes; Oblique scale rows slanting downward above lateral line closely approximate number of lateral-line scales. Lateral-line scales 51-55 (usually 52 or 53), anterior 2-21 scales bearing a small spine or ridge. First dorsal fin spinous, base length moderate, first spine very short, connected by a low membrane to second, following spines much longer. Second dorsal fin base longer than first, anterior rays longest, nearly as long as longest first dorsal spines. Anal fin similar in shape, opposite and slightly longer-based than second dorsal fin. Caudal fin rounded.
Size	Maximum total length about 25 cm, commonly to 20 cm TL.
Colour	Head and body orange-brown or grey above, whitish below, about 6 obscure dark bands across back. Caudal fin pale with about 3 series of black spots over entire fin, becoming larger and more elongated ventrally; pectoral and pelvic fins with large brown spots, sometimes forming weak bands.
Feeding	Presumably feeds on other fishes and invertebrates.
Biology	The Rusty Flathead undergoes a protandrous sex change, whereby most mature males change sex into females. Individuals reportedly have overlapping home ranges and the species is thought to have a promiscuous mating system.
Fisheries	Taken by trawls over sand and mud bottom.
Conservation
Etymology	The species name japonica is for Japan, the type locality.
Species Citation	Platycephalus japonicus Cuvier 1829 (ex Tilesius) Histoire naturelle des poissons 4: 1829: 256. Type locality: Nagasaki, Japan.
Author	CSIRO Marine & Atmospheric Research & Bray, D.J. 2017
Resources	Australian Faunal Directory

Rusty Flathead, Inegocia japonica (Tilesius 1812)

References

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Whitley, G.P. 1933. Studies in Ichthyology No. 7. Records of the Australian Museum 19(1): 60-112 figs 1-4 pls 11-15 (as Levanaora isacanthus)