Monodactylids are schooling fishes found in estuarine and coastal marine waters. Two genera and three species occur in temperate Australia.

Diamondfish, Monodactylus argenteus
A school of Diamondfish at a depth of 3 m, Manly, Sydney, New South Wales, 26 Feb 2011. Image: Gaetan Guilhon
© Gaetan Guilhon

Monodactylids are schooling fishes found in estuarine and coastal marine waters, sometimes also in fresh water, in tropical to temperate regions of western Africa and the Indo-Pacific (Nelson 1994; Kottelat, 200; Allen et al, in press). There are three genera and seven species in the family. Two genera and three species occur in temperate Australia (Kuiter 1993, 1996; Gomon et al., 1994; Allen et al, in press). Adults (to 25cm) are deep bodied and strongly compressed, have long-based dorsal and anal fins roughly equal in length and dorsal and anal fins that are elongated anteriorly. Eggs of M. sebae are pelagic in sea water (they sink in fresh water), and spherical, 0.6-0.7 mm in diameter, while eggs of M. argenteus are demersal and adhesive at least in fresh water (Breder & Rosen, 1966). Larvae have been described for M. argenteus and M. sebae (Kinoshita, 1988; Miskiewicz, 1989, 1998, 2000; Akatsu et al., 1997). The moderate head spination, and the early forming, elongate pelvic fins in Monodactylus are the only apparent specialisations of monodactylid larvae to pelagic life (Miskiewicz, 1989, 2000).

Meristic characters of monodactylid genera of temperate Australia
(n) Dorsal Anal Pectoral Pelvic Caudal Vertebrae
Monodactylus (1) VII-VIII 26-31 III 26-31 16-18 I 5 17 10 + 14 = 24
Schuettea (2) V 28-30 III 28-32 14-18 I 5 17 10 + 14 = 24

Main characters of monodactylid larvae

  • 24-25 myomeres
  • Body moderate to deep (BD 30-59%)
  • Body depth is approximately equal to head length
  • Moderate head spination, including weak to moderate preopercular spines, a low supraocular ridge, and small interopercular, posttemporal and supracleithral spines
  • Gut moderate to long (PAL 43-62%), coiled and compact
  • Early forming, heavily pigmented pelvic-fin rays in Monodactylus, elongate in early stages but reducing in size with growth
  • Long based dorsal and anal fins with similar numbers of elements
  • Band of pigment primarily through trunk that varies in strength ontogenetically and among species

References to monodactylid larvae

  • Akatsu et al. (1977), Ogasawara et al. (1978), Johnson (1984), Kinoshita (1988), Miskiewicz (1989, 1998, 2000).

Families with similar larvae

  • Nomeidae (e.g. Nomeus, Psenes) - 30-42 myomeres; weak or absent preopercular spination; long-based dorsal fin with > VII spines.
  • Pempheridae - Weak preopercular spines, supraocular ridge absent; early forming pelvic fins, fins located high and laterally on gut in early stages, short based dorsal fin.
  • Phycidae - 38-55 myomeres; no preopercular spines; prominent pterotic spines in some taxa; long-based, spineless dorsal and anal fins; pelvic fins inserted high and laterally on body; barbels on lower jaw and snout in a few taxa; pigmented bands usually along tail.
  • Trachichthyidae - 26-30 myomeres; usually prominent preopercular and opercular spines; short-based dorsal and anal fins, III-X, 8-18 and II-III, 8-11 respectively; pelvic fin I, 6; body moderately to heavily pigmented


  • Akatsu, S., Ogasawara, Y. & Yasuda, F. (1977). Spawning behaviour and development of eggs of the striped fingerfish Monodactylus sebae. Japanese Journal of Ichthyology 23: 208-214.
  • Allen, G. R., Cross, N. & Allen, C. (in press). Monodactylidae: diamondfishes, moonfishes, silver batfishes in : Hoese, D.F., Bray, D. J., Allen, G. R., Allen, C. J., Cross, N. J. & Paxton, J. R. (eds) Pisces (part 2). Zoological Catalogue of Australia vol 7 (part 2) Canberra: Australian Government Publishing Service.
  • Breder, C. M., Jr. & Rosen, D. E. (1966). Modes of reproduction in fishes. Distributed by T.F.H. Publications, Neptune City, New York. 941 pp.
  • Gomon, M.F., Glover, J.C.M. & Kuiter, R.H. (1994). The fishes of Australia's south coast. State Print, Adelaide, South Australia. 992 pp.
  • Johnson, G. D. (1984). Percoidei: development and relationships. In: Ontogeny and systematics of fishes. pp 464-498. Moser, H. G., Richards, W. J., Cohen, D. M., Fahay, M. P., Kendall Jr., A. W. & Richardson, S. L. (Eds). Am. Soc. Ichthyol. Herpetol., Spec. Publ. 1.
  • Kinoshita, I. (1988). Monodactylidae. In: An atlas of the early stage fishes in Japan, pp. 507-508. Okiyama, M. (Ed). Tokai University Press, Tokyo. (In Japanese).
  • Kottelat, M. (2001). Monodactylidae. Moonfishes. In: FAO species identification guide for fishery purposes. The living marine resources of the Western Central Pacific. Volume 5. Bony fishes part 3 (Menidae to Pomacentridae). pp. 3216-3220. Carpenter, K.E. & Niem, V.H. (Eds.). Rome, FAO.
  • Kuiter, R.H. (1993). Coastal fishes of south-eastern Australia. Crawford House Press, Bathurst. 437pp.
  • Kuiter, R.H. (1996). Guide to Sea Fishes of Australia: A Comprehensive reference for divers and fisherman. New Holland Publishers, Sydney. 433 pp.
  • Miskiewicz, A.G. (1989). Family Monodactylidae. In: The Larvae of the Indo-Pacific Shorefishes. pp 196-199. Leis, J.M. & Trnski, T. (Eds). University of New South Wales Press, Sydney.
  • Miskiewicz A.G. (1998). Monodactylidae: Diamondfishes, fingerfishes. In: Larvae of temperate Australian fishes: laboratory guide for larval fish identification. pp 250-253. Neira, F. J., Miskiewicz, A. G. & Trnski, T. (Eds). University of Western Australia Press, Perth.
  • Miskiewicz, A.G. (2000). Monodactylidae (Diamondfishes, Moonies, Fingerfishes). In: The larvae of Indo-Pacific coastal fishes: an identification guide to marine fish larvae. pp 351-354. Leis, J. M. and Carson-Ewart, B. M. (Eds.). Fauna Malesiana Handbooks 2. Brill, Leiden.
  • Nelson, J. S. (1994). Fishes of the world. Third edition. John Wiley and Sons, New York. 600pp.
  • Ogasawara, Y., Akatsu, S & Taki, Y. (1978). Juvenile stages and the effect of salinity on the survival of larvae and juveniles of the striped fingerfish Monodactylus sebae. Japanese Journal of Ichthyology 24: 246-250.