Slender Hardyhead (species: Atherinomorus lacunosus) in ALA: Lizard Island (Lizard Island Field Guide)
Atherinomorus lacunosus
Slender Hardyhead

©Paul Asman: Atherinomorus lacunosus at Lizard Island.

©Paul Asman: Atherinomorus lacunosus at Lizard Island.

©Lyle Vail: Atherinomorus lacunosus on the reef flat on the SE side of South Island, Lizard Island Group. Note body length is about 5.5 times body depth and very large eye.
Kingdom Animalia
Phylum Chordata
Class Actinopterygii
Order Atheriniformes
Family Atherinidae
Genus Atherinomorus
Species Atherinomorus lacunosus



Distinguishing features

A small silvery fish with a large eye and an iridescent stripe along the side of the body, always seen in large schools close to the shoreline. Body length is 4.1 to 5.6 times body depth according to Allen and Erdmann (2012).

Atherinids have two widely-separated dorsal fins and the pectoral fin inserted high on the side.


  • Up to 13 cm (length according to Allen and Erdman, 2012)
  • Up to 7 cm (Length of specimens commonly observed around Lizard Island.)

Depth range

  • Depth range data is not yet available.


Similar taxa


©Atlas of Living Australia: Australian distribution

Distribution and habitat preferences

Pelagic (dwells near the water surface) but aggregates in large schools over reef areas near rocky shorelines and mangroves.

Often found near the mangroves at Mangrove Beach, and can be periodically seen close to rocky shores in other bays of the island.


Hardyheads are plankton feeders, and a major food source for predators when they aggregate near the island in summer. They will jump en masse when attacked, making a spectacular silvery shower.

Web resources


References that assist with identification

  • Allen and M.V. Erdmann, G.R. (2012). Reef fishes of the East Indies. Volumes I-III in: Reef fishes of the East Indies. Tropical Reef Research, Perth, Australia. LIRS catalog number 90162.

Other references

  • Conand, F. (1993). Life history of the silverside Atherinomorous lacunosus (Atherinidae) in New Caledonia, Fish Biology, 42: 851-863. LIRS catalog number 90016.