Bluebottle-fish, Nomeus gronovii (Gmelin 1789)

Other Names: Bluebottle Fish, Portuguese Man-o'-war Fish, Portuguese Man-o-war Fish, Shepherd, Shepherd Fish

A juvenile Bluebottle-fish, Nomeus gronovii, at Shiprock, Port Hacking, New South Wales, January 2022. Source: Harry Rosenthal / License: CC by Attribution-NonCommercial

The striking pelagic juveniles shelter amongst the tentacles of floating Bluebottles (Physalia or Portuguese Man-o-War) which are colonial animals called siphonophores (not jellyfish). Bluebottle-fish are silvery-white with a dark blue back, dark blue markings on the sides, large dark fan-like pelvic fins and a deeply forked tail. Adults live near the bottom and are mostly dark brown with large dark pelvic fins.
Although juvenile Bluebottle-fish are not completely immune to the toxin in the stinging tentacles of the man-o-war, they shelter around the siphonophore for protection. 
Great video of juvenile Bluebottle-fish swimming around the tentacles of a floating Bluebottle.

Cite this page as:
Bray, D.J. 2022, Nomeus gronovii in Fishes of Australia, accessed 13 Jul 2024,

Bluebottle-fish, Nomeus gronovii (Gmelin 1789)

More Info


Fremantle, Western Australia, and off Cape York Queensland to eastern Victoria. Although in Australia, the species mostly occurs in tropical waters, individuals are occasionally seen in southern areas, especially during summer months when Bluebottles (Physalia) are present; also recorded from Lord Howe Island in the Tasman Sea. Elsewhere, the species is circumglobal in tropical and warm temperate seas. 
Juveniles are pelagic in surface oceanic waters, and may drift or be blown inshore with floating Bluebottles (Portuguese man-of-war). Adults live near the bottom deeper waters.


Dorsal fin IX–XII + I, 24–28; Anal fin I–II, 24–29; Caudal fin17; Pectoral fins 19–24; Pelvic fins I, 5; Lateral line ~ 65; Gill rakers 8 + 1 + 14–18; Vertebrae 41.

Body elongate oval of moderate depth (21-39% SL), strongly compressed; caudal peduncle short, slender. Head of moderate size (25-39% SL), compressed; snout bluntly rounded; eyes large (approx. 28% HL); mouth large, maxillae reaching below front of eyes, slightly oblique; teeth of moderate size, each jaw with single row, small teeth on vomer but none on tongue.

Scales small, thin and easily dislodged, extending forward on head to between orbits; lateral line close to and following profile of back. Numerous small pores on head. 

Two dorsal fins: first dorsal membranous with slender spines, moderately high and angular with slightly rounded hind margin, originating above pectoral fin bases; second dorsal long and low, outer margin about parallel with profile of back; anal fin similar to and opposite second dorsal; caudal fin deeply forked, fin tips pointed, upper and lower lobes crossing like scissors. Pectoral fins well developed, rounded, not quite reaching anus. Pelvic fins thoracic, large and fan like in juveniles, of moderate size in adults.


Juveniles bright blue on back, sides silvery with blue blotches and spots; first dorsal fin dark blue; large dark blue blotches basally on second dorsal, anal, caudal and pectoral fins with smaller blotches distally on second dorsal and anal; pelvic fins mostly blackish. Adults mostly dark brown.


Juveniles feed on the tentacles and gonads of Physalia, Portuguese man-o-war, and on zooplankton.


The species is named in honour of Dutch naturalist Laurens Theodorus Gronovius.

Species Citation

Gobius gronovii Gmelin, 1789, Systema Naturae 1(3): 1205.Type locality: America.


Bray, D.J. 2022


Atlas of Living Australia

Bluebottle-fish, Nomeus gronovii (Gmelin 1789)


Allen, G.R., Hoese, D.F., Paxton, J.R., Randall, J.E., Russell, B.C., Starck, W.A., Talbot, F.H. & Whitley, G.P. 1976. Annotated checklist of the fishes of Lord Howe Island. Records of the Australian Museum 30(15): 365-454 figs 1-2

Dooley, J., Collette, B., Aiken, K.A., Marechal, J., Pina Amargos, F., Kishore, R. & Singh-Renton, S. 2015. Nomeus gronovii (errata version published in 2016). The IUCN Red List of Threatened Species 2015: e.T16545183A103978497. Accessed on 10 January 2022.

Gmelin, J.F. 1789. Pisces. pp. 1126-1516 in Linnaeus, C. (ed.). Systema Naturae. Leiden : Delamollière Vol. 1 Pt 3. See ref at BHL

Grant, E.M. 1991. Fishes of Australia. Brisbane : EM Grant Pty Ltd 480 pp.

Haedrich, R.L. 1967. The stromateoid fishes; systematics and a classification. Bulletin of the Museum of Comparative Zoology, Harvard 135(2): 31-139 figs 1-56

Jenkins, R.L. 1983. Observations on the commensal relationship of Nomeus gronovii with Physalia physalis. Copeia 1983(1): 250-252.

Johnson, J.W. 1999. Annotated checklist of the fishes of Moreton Bay, Queensland, Australia. Memoirs of the Queensland Museum 43(2): 709-762.

Kato, K. 1933. Is Nomeus a harmless inquilinus of Physalia?. Proc. Imp. Acad. Japan 9: 537-538.

Kuiter, R.H. 1993. Coastal Fishes of South-eastern Australia. Bathurst : Crawford House Press 437 pp.

Last, P.R. 2001. Nomeidae, Ariommatidae, Tetragonuridae. pp. 3771-3785 in Carpenter, K.E. & Niem, T.H. (eds). The Living Marine Resources of the Western Central Pacific. FAO Species Identification Guide for Fisheries Purposes. Rome : FAO Vol. 6 pp. 3381-4218.

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McDowall, R.M. 1994. Family Nomeidae. pp. 839-843, figs 742-745 in Gomon, M.F., Glover, C.J.M. & Kuiter, R.H. (eds). The Fishes of Australia's South Coast. Adelaide : State Printer 992 pp. 810 figs.

Parin, N.V. & Piotrovsky, A.S. 2004. Stromateoid fishes (suborder Stromateoidei) of the Indian Ocean (species composition, distribution, biology, and fisheries). Journal of Ichthyology 44(Suppl. 1): 33-62.

Pepperell, J. 2010. Fishes of the Open Ocean a Natural History & Illustrated Guide. Sydney : University of New South Wales Press Ltd 266 pp.

Whitley, G.P. 1931. New names for Australian fishes. The Australian Zoologist 6(4): 310-334 1 fig. pls 25-27 (described from Shellharbour, New South Wales, as Nomeus dyscritus)

Quick Facts

CAAB Code:37446009

Behaviour:Shelters beneath Bluebottles (juvs)

Conservation:IUCN Least Concern

Depth:0-1000 m

Habitat:Pelagic (juv), benthopelagic (adults)

Max Size:39 cm TL

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Species Maps

CAAB distribution map