Mildura Riverfront Shared Path - Ranfurly Rock Bar

Rock Bars occur along the Murray River providing habitat and shelter for a diverse range of aquatic animals including yabbies, shrimp, frogs and tadpoles, turtles and fish. Along with submerged trees and branches, known as snags, these rock bars are extremely important for aquatic life, particularly native fish. Snags and rock bars provide a wide range of habitat by creating variability in water depth, flow and temperature. They also contribute to the chemical composition of the water by releasing carbon (snags) and minerals (rocks) into the water.

There are around 45 native fish species in the Murray Darling Basin, with many of these such as Golden Perch and Murray Cod relying on snags and rock bars for a number of reasons, including providing the following:

• sites to attach adhesive eggs during breeding;
• sites to rest from fast river flows;
• shelter from predators;
• landmarks to define territories and aid navigation; and
• ambush sites.

Macro-invertebrates

Macro-invertebrate is a term used to describe animals that have no backbone and can be seen with the naked eye. These animals generally include insects, crustaceans, molluscs, arachnids (spiders) and annelids (worms). Some water macro-invertebrates can be quite large, such as freshwater crayfish, shrimp and yabbies, however, most are very small. These creatures are an important food source for many water animals including fish, frogs and turtles. Macro-invertebrates use rock bars and snags for shelter and a food source, by grazing on the microbes and algae that grow on them.

Case Studies

Murray Cod

Identification

The Murray Cod is Australia’s largest freshwater fish, reaching around 110kg and 1.8metres in size. It is easily identified by its large mouth, cream to white belly and green mottled pattern on the body and head. The tail is rounded and adults have a broad head with a concave profile.

Biology and Habitat

Murray Cod are generally associated with deep holes in the river and prefers habitat with in stream covers such as that provided by snags and rock bars. They are a ‘sit and wait’ predator with a diet including fish, yabbies and frogs.

The Murray Cod matures at 4-5 years of age and breeds in early spring to late summer, when water temperatures exceed about 15 degrees Celsius. The eggs are adhesive and usually deposited onto a hard surface such as snags and rocks.

Did you know?

The male Cod guards the eggs during the 5 to 13 day incubation period.

Golden Perch

Identification

The Golden Perch is a medium to large fish with a deep laterally compressed body. They can reach approximately 23kg and 76cm in length. They are generally olive-green with a yellow or cream belly. They have a large mouth with the lower jaw protruding slightly and a rounded tail.

Biology and Habitat

The Golden Perch is generally found in deep, slow flowing pool habitats around snags and other underwater shelters such as rock bars. Adult and immature fish are migratory and extensive upstream movements of more than 1000km have been recorded for some adult fish. They are an opportunistic carnivore with a diet consisting mainly of shrimp, yabbies, small fish and aquatic insect larvae.

Did you know?

The female Golden Perch can hold up to 500,000 eggs.

Mildura Riverfront Shared Path

Published with permission of Mildura Rural City Council