River blackfish

Description

Long rounded body. Very small scales. Long, low dorsal and anal fins, with the dorsal fin appearing to be joined with the rounded tail fin, but actually separate. The pelvic fins are located on the underside of the body below the gills, and consist of one or two rays. Large head with rounded snout, low placed mouth which reaches back to the front edge of the eye. Lower jaw is shorter than the upper. Moderate sized eye located high on the head. Body invariably has a heavy coating of slime. Dorsal fin has 6-13 spines (as distinct from the two-spined blackfish, G Bispinosus).

Colouring is highly variable, mottled yellowish, brownish-green or grey, but also dark brown to a light bluish or greenish-brown with blotches on the upper body, with many irregular darker blotches. Lower body may be light blue, yellow or purple. Fins olive-brown to black.

Distribution

Widespread in Victoria, both north and south of the Great Dividing Range. Common throughout most of its range.

Habitat

Although it is found in a variety of habitats, it is most common in cooler, flowing streams where there is plenty of rock cover with abundant snags, fallen timber and debris, and gravel bottom. A bottom dwelling fish. Also occurs in slow-flowing lowland rivers, coastal and in-land lakes, and reservoirs.

Brief Biology

Can grow to 60 cm and 5 kg, but is usually less than 30 cm and 450 g. The number of eggs per female depends on body length. Relatively few eggs are laid, with a female of 30 cm laying about 500 eggs. Spawning occurs in spring and early summer when water temperatures reach about 16°C.

The strongly adhesive eggs are laid in hollow logs and rock cavities and have been found inside pieces of discarded PVC piping. Observations suggest that the male guards the eggs. Young fish hatch about a fortnight later, and at about 5 weeks old are actively swimming and seeking food. Confined as they are to the bottom and spending much of their time in the leaf litter and debris, predation on the young by crustaceans and dragonfly nymphs can be heavy.

The species will breed in streams and lakes, and has been known to breed in farm dams where suitable habitat is available. A carnivorous fish, eating a wide variety of aquatic insects, molluscs, crustaceans, smaller fishes and terrestrial invertebrates that fall into the water. Diet varies with locality and abundance of available food.

Other Notes

River blackfish (and the more recently described two-spined river blackfish) are unique to Australia. An excellent angling species with sweet tasting flesh. Furtive and secretive, they move mainly at night, late evening and early morning in search of food.

bundance has been affected in some areas due to human impact, including increased siltation of streams due to changed land usage, clearing of debris from streams (de-snagging), changed stream flow regimes resulting from the construction of water storages and in some cases competition from introduced fish such as trout.