28KK
jpeg.60mm (2.4in) TL. Ross Felix photo. ATHERINIDAE, Haryheads or silversides
28KK
jpeg.60mm (2.4in) TL. Ross Felix photo.
The largest recorded is 78mm (3in) SL. They are commonly found up to 50mm (2in).
It is listed as Vulnerable by the Australian Society for Fish Biology.
Restricted to approximately seven springs at Dalhousie Springs (shown by the black dot). They are usually very abundant.
Dalhousie hardyheads occur in the wild at temperatures from 20°C to 40°C (68 to 104°F) and make very brief excursions into water of 41.8°C (107°F). This is the highest recorded voluntary temperature tolerance of any Australian fish and one of the hottest voluntary temperatures that fish have been recorded at anywhere in the world!. They are generally found in the pools and channels in the spring outflows. The minimum dissolved oxygen tolerated is 0.5 mg O2/L. Their diet consists mostly of green filamentous algae but also includes ciliates, ostracods, insects, hydrobiid snails, detritus, and worms (Glover 1989).
Dalhousie hardyhead is the only member of the genus known to be morphologically sexually dimorphic. Virtually nothing is known of reproduction in the wild. In aquaria they are easily spawned. They probably lay in excess of around 20 eggs a day when temperatures are maintained over 24°C (75°F). Their upper spawning temperature is yet to be investigated. They readily spawn on mops, most spawning activity takes place in the morning. They also readily eat their eggs. At 28°C (83°F) eggs take about 7 days to hatch. Fry are about 5mm (0.2in) TL at hatching. Fry are usually first fed vinegar eels until they are large enough to ingest baby brine shrimp. Fry typically grow slowly in aquaria. It is not known whether they reproduce throughout the year or seasonally under natural conditions.
The greatest threat is their restricted range. At Dalhousie Springs, the dominant threat is the potential introduction of exotic species, however no introductions have been recorded yet.
Dalhousie Springs is completely enclosed within Witjira National Park. There is also ongoing population monitoring being conducted by Bryan Pierce from the South Australian Research and Development Institute.
Continue regular population monitoring.
Glover, C. J. M. 1989. Fishes. In, Natural History of Dalhousie Springs. Eds. Zeidler, W. & Ponder, W. F. South Australian Museum, Adelaide. pp 89-112.
Ivantsoff, W. I. & Glover, C. J. M. 1974. Craterocephalus dalhousiensis n.sp., a sexually dimorphic freshwater teleost (Atherinidae) from South Australia. Australian Zoologist. 18: 88-98.
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This file was last modified: 18 March 2003