Brown trout

Description

Thick body with a large head, and a large mouth extending backwards to below the eye. A very distinct lateral line with 110-120 scales. Tail fin is slightly forked. Colour varies considerably, reflecting the age of fish as well as habitat and food. Usually brown to olive on the upper body. Dark spots on the upper body, upper fins and gill covers. Below the lateral line body colour is lighter with some red spots.

Many brown trout have a red halo around the larger dark spots. Few if any spots on the tail.

Sea run fish such as occur in Port Phillip Bay may be olive-green on the back, with silvery sides and very few and indistinct spots on the sides.

Distribution

Widespread and common through much of Victoria. Self-maintaining populations exist in many waters.

Habitat

Cool, well-oxygenated waters, usually in gravel-bottomed streams with a moderate to swift flow, but also in cool, clear lakes and impoundments. Optimum temperature range 4-19°C. Some brown trout in coastal streams move out to sea, and small numbers are taken in Port Phillip Bay.

Good quality brown trout can only be produced in rivers where habitat conditions are suitable. Extensive local and overseas research has identified the types of habitat preferred by trout and which give the best spawning success and survival, as well as fast growth rates, resulting in good numbers of larger fish. The ideal trout stream should have spawning areas of gravel, with water depths 20-100 cm deep and fast flowing water, 30-100 centimetres per second (cm/sec).

Water temperature during the spawning season (May/June) should be about 2-12°C. Adult brown trout prefer to rest against the bank, protected from overhead view, and in water more than 45 cm deep but with water velocities between 5 and 30 cm/sec. They prefer to move, feed and forage in water more than 45 cm deep, although they can pass through barriers and riffles with shallower water. Extensive areas of water over 70 cm deep will facilitate good growth rates resulting in numbers of large-sized fish. Extensive areas of coarse substrate (gravel and rubble) in water 20-100 cm deep, and with water velocities of 30-100 cm/sec, will produce good quantities of macroinvertebrates (e.g. mudeyes, mayfly, stonefly, snails and shrimp) to provide food for fish growth.

The optimum water temperature range for best metabolism of this food and therefore maximum growth is from 7-17°C. Juvenile trout seek cover and protection from larger predatory fish by living in riffles with coarse substrate and water depths of 15-45 cm. The juvenile trout avoid the higher water velocities, which often occur in the riffles, by sheltering within the coarse substrate.

Any river in Victoria with such conditions will produce good numbers of large brown trout. The most significant limiting factors in the production of large brown trout in Victorian rivers are high water temperatures and a scarcity of water over 70 cm deep. The reason why the Kiewa River produces good numbers and size of brown trout is that their preferred habitat conditions are present in this river. Closed seasons, bag limits or size limits help to share the catch; stocking is useful if spawning has failed but, in the absence of good habitat, regulations or stocking won't result in good numbers of large river trout in the angler's creel.

Brief Biology

Spawning occurs, usually at three years of age, during autumn-winter often following a flood, typically in small tributaries with gravel beds. Males may become sexually mature at 2 years of age.

Female fish excavate depressions in the stream bed with their tail. Females lay an average of 1,600 eggs for each kilogram of body weight. After spawning, the eggs are covered by dislodging gravel upstream of the spawning site. Mature males develop a curved bottom jaw that develops into a hook.

Brown trout are carnivorous and largely a sight feeder, young fish feeding throughout the water column, the more mature fish feeding mainly on the bottom. Diet includes insects, crustaceans, molluscs, worms and small fish such as minnows (galaxiids).

Few brown trout in Victoria live beyond 5-6 years.

Management

The brown trout fishery in Victoria is roughly divided into two parts. The eastern half of Victoria has mainly self-supporting populations which exist where suitable habitat is available, whilst most suitable waters in the western half of the State depend on stocking with hatchery-produced fish.

Other Notes

Introduced to Australia via Tasmania in 1864 through the first successful importation of fertilised eggs after more than 20 years of efforts by various persons and groups.

May exceed 1 metre in length and 16 kg in weight in its native habitat of Europe and Western Asia, and is known to have reached 900 mm and 14 kg in Australia, but the species in Victoria is commonly much smaller, achieving weights of up to 8 kg.

Given good habitat and food, brown trout develop rapidly in the second and third years. Considered to be a 'residential' fish as it is very territorial and mature fish are likely to stay in a limited area for their lifetime. Brown trout appears to dominate rainbow trout in waters where both species exist naturally or have been stocked.

Many naturally self-supporting populations of brown trout occur in Victoria, and quite a few of these populations have reached numbers of fish which over-tax the available food supply. This results in either populations of fish that continue to grow but the majority of fish are poor in condition (e.g. Lake Dartmouth), or stunted populations which may contain 2 and 3-year-old fish of 275-400 g (e.g. Cobungra River, Jim Crow Creek)

Regulations

Recreational Fishing Licence requirements, and the regulations affecting the taking of brown trout in Victoria, are provided in the Victorian Recreational Fishing Guide, available free from RFL sales agents and DEDJTR Offices and Information Centres.

Further Reading

• A Guide to the Freshwater Fish of Victoria, Phillip Cadwallader & Gary Backhouse, Department of Conservation and Environment.
• Australian Freshwater Fishes, John R. Merrick & Gunther E. Schmida.
• Salmonids in the Antipodes, John Clements.