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The Murray hardyhead (Craterocephalus fluviatilis) is a small, slender freshwater fish endemic to the Murray-Darling Basin in southeastern Australia. It is characterized by its silvery body, relatively large eyes, and two distinct dorsal fins. This species is a member of the family Atherinidae, commonly known as hardyheads or silversides. It is a schooling fish, typically found in shallow, still, or slow-flowing waters with abundant aquatic vegetation.
Physical Characteristics
- Body shape
- elongated
- Coloration
- Silvery body, often with a faint lateral stripe. Dorsal surface can be olive-brown to grey, fading to silvery-white on the belly. Fins are generally translucent.
- Scale type
- cycloid
- Mouth position
- terminal
- Distinctive features
- Two distinct dorsal fins, well separated., Relatively large eyes., Slender body., Absence of a lateral line.
- Dorsal fin
- Two dorsal fins; the first is small with 4-7 spines, the second is larger with 1 spine and 6-9 soft rays. The two fins are distinctly separated.
- Tail fin
- Forked caudal fin.
- Pectoral fin
- Pectoral fins are moderately sized, located high on the body.
- Distinctive fins
- Pelvic fins are small, located abdominally, with 1 spine and 5 soft rays. Anal fin has 1 spine and 8-11 soft rays.
Identification Tips
Dorsal Fins
Look for two clearly separated dorsal fins. The first is spiny and much smaller than the second, which has a spine and soft rays.
Body Coloration
Observe the silvery body with a darker back and lighter belly. A faint lateral stripe may be present.
Eye Size
Note the relatively large eyes in proportion to its head.
Size
Adults are typically small, rarely exceeding 7 cm in total length.
Habitat
- Water type
- freshwater
- Depth
- Typically found in shallow waters, often less than 1 meter deep.
- Environment
- Prefers still or slow-flowing waters of rivers, billabongs, wetlands, and ephemeral lakes. Often associated with dense aquatic vegetation (e.g., Myriophyllum, Potamogeton) which provides cover and foraging opportunities. Tolerant of a wide range of salinities, from fresh to slightly brackish (up to 10 ppt).
- Geographic range
- Endemic to the Murray-Darling Basin in southeastern Australia, primarily in isolated populations within New South Wales, Victoria, and South Australia. Historically more widespread, but now restricted to fragmented habitats.
Aquarium Information
- Care level: intermediate
- Temperament: peaceful
- Diet: omnivore
- Minimum tank size: 75 liters (20 gallons)
- Temperature: 15-28°C (59-82°F)
- pH level: 7.0-8.5
- Hardness: 100-300 ppm (moderate to hard)
- Compatibility: Peaceful and suitable for community tanks with other small, non-aggressive fish. Best kept in schools of 6 or more individuals.
- Special requirements: Requires well-oxygenated water, good filtration, and plenty of aquatic vegetation for cover and spawning. Sensitive to poor water quality and sudden changes in parameters. A sandy or fine gravel substrate is preferred.
Wild Information
- Conservation status: endangered
- Seasonality: Breeding typically occurs during spring and summer months when water temperatures are warmer.
- Market price: Not commercially fished for consumption; occasionally available in the aquarium trade as a conservation species.
- Commercial importance: none
- Taste: Not typically consumed due to small size and conservation status.
- Texture: Not typically consumed due to small size and conservation status.
- Nutritional value: Not typically consumed due to small size and conservation status.
Key Facts
Conservation Statusinteresting
The Murray hardyhead is listed as Endangered under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) and various state legislations, primarily due to habitat loss, degradation, and altered flow regimes.
Salinity Toleranceamazing
Unusually for a freshwater fish, Murray hardyheads exhibit a remarkable tolerance to a wide range of salinities, from fresh to slightly brackish water, which has allowed them to persist in some saline wetland environments.
Ecological Rolebehavior
As a small, schooling fish, the Murray hardyhead plays an important role in its ecosystem as both a consumer of small invertebrates and algae, and as a food source for larger predatory fish and birds.
Reproductionbehavior
They are egg-scatterers, typically laying adhesive eggs on aquatic vegetation. Spawning occurs multiple times during the breeding season.
Safety Information
Safe- Safety level: safe
- Venomous: No
- Edibility: not recommended
- Handling notes: No specific handling precautions are required beyond general care for small, delicate fish. Avoid excessive handling to minimize stress and injury.
Similar Species
Darling River hardyhead
Craterocephalus amniculus
The Darling River hardyhead generally has a more robust body and a shorter snout. Fin ray counts can also differ, though this requires close examination. C. amniculus typically has fewer anal fin rays (7-9 vs. 8-11 for C. fluviatilis) and fewer lateral line scales.
Smallmouth hardyhead
Craterocephalus stercusmuscarum
The Smallmouth hardyhead typically has a more pointed snout and a smaller mouth. Its geographic range is also more northerly, though there can be some overlap. Morphometric analysis is often required for definitive differentiation.
Scientific Classification
- Kingdom
- Animalia
- Phylum
- Chordata
- Class
- Actinopterygii
- Order
- Atheriniformes
- Family
- Atherinidae
- Genus
- Craterocephalus
- Species
- fluviatilis
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