Craterocephalus

The fly-specked hardyhead, Craterocephalus stercusmuscarum stercusmuscarum, is an atherinid endemic to Australia. It ranges from the Northern Territory to southern Queensland and forms large shoals over barren sand, mud or clay in streams, rivers, lakes and ponds. Skittish and rarely seen in the trade outside Australia, it does far better in a shoal of at least 8-10. Genetic differences between neighbouring populations are in some cases large enough to suggest several distinct species.