Trout were first introduced into New South Wales in 1873. They were brown trout, Salmo trutta brought up from Tasmania, where they had been introduced in 1868.
Importation of brown trout continued until 1888. In 1890, eggs of the rainbow trout, Oncorhynchus mykiss and the brook trout, Salvelinus fontinalis, were imported from New Zealand and the first hatcheries commenced operation.
The Atlantic salmon, Salmo salar, was introduced from Nova Scotia in 1963-65 and the brook trout was re introduced from Tasmanian stocks in 1967.
Nowadays, NSW DPI regularly stocks selected streams and dams with fry and fingerlings of all four species. The fish are bred at Gaden Hatchery Jindabyne (Snowy Mountains), and at L P Dutton Hatchery, Ebor, near Armidale.
Water temperature is the main factor in determining trout distribution in NSW. Basically, trout are found in the cool headwaters of streams along the Great Dividing Range, from the Clarence and Macleay rivers in the north to the Snowy River in the south.
Trout abundance varies. Some stocks in mountain streams (with suitable gravel bottoms for breeding) can maintain their numbers but many other waters (eg dams, lowland streams) need regular restocking.
Trout farming in NSW began in the early 1970s, and now there are a number commercial farms. Apart from producing fish for the market, some specialise in eggs for export, in fingerlings for stocking farm dams, or in enticing the tourist with aquariums and fishouts. The most popular species is the rainbow trout, being the easiest to culture and having a ready market.
The rainbow trout is also the main species cultured in Victoria (also in freshwater); it is sold fresh or smoked. In Tasmania, rainbow trout are grown in both freshwater and saltwater and Atlantic salmon in saltwater.
For the production figures see the NSW DPI aquaculture production reports.
In the hatchery, wild or captive female trout are stripped and the eggs fertilised by mixing with milt from the males. The eggs are then put into tanks of circulating water where they hatch after 4-14 weeks, depending on the water temperature. When the yolk sac has been absorbed and the pigment has developed, the young trout are put in outdoor ponds to grow to market size.
Water temperatures 4-19°C are considered suitable for maintaining brown trout; 10-22°C for rainbow trout. For spawning and egg production, brown trout need 6-10° C and rainbow trout 9-14°C.
Trout take 4-12 weeks to become fry (big enough for stocking dams). The fingerling size (8-10 cm) is reached after 6 months and market size (250-350 g) takes about a year.
Growth of both rainbow and brown trout is best at about 15°C.
The holding capacity of a pond depends upon its volume, flow and temperature and size of fish. Pond water should be totally renewed every hour. Well oxygenated, cool to cold, and have low suspended solids for best growth.
Trout will take artificial pelleted feed. They need high protein diets (30-35% for rainbow and brook trout, 50% for brown trout and Atlantic salmon).
In practice, 2 kg of feed is needed to produce 1 kg of fish (conversion ratio 2:1). Conversion as good as 1.2:1 is possible, particularly under tank culture.
Poor hygiene is the most common cause of bacterial disease in hatcheries, where any disease can spread rapidly if not identified and treated. Trout are more vulnerable to disease if stressed. Temperature stress (above 19° C) is the main problem in NSW, then overcrowding and low oxygen. Common parasites include Ichthyophthirius ('Ich' or 'whitespot') and Trichodina, both protozoans.
Introduced diseases now in our rivers are causing concern. In particular, outbreaks of trout EHN virus in farms have resulted in new quarantine policies.
Trout need clean, well-oxygenated water at suitable temperatures. Silt-free water is essential for egg hatching and fry development.
Seawater aquaculture of salmonids has not been thoroughly investigated in New South Wales but water temperatures, even in the south of the State, would probably be too high for survival and for continuous growth through the year.
A licence from the Dept of Environment and Climate Change is needed to return effluent water to natural waterways and all water must first pass through a settlement pond.
Trout have high meat yields and sell well. They command medium prices for quality fish. Fresh trout has become cheaper than other prime fish such as snapper, mulloway and barramundi. See the NSW DPI aquaculture production reports for average price figures.
At present, a few large producers dominate the market. Value-added products (eg smoked trout) demand higher prices. New marketing techniques (eg. fillets and cutlets in supermarkets) are being developed.
Atlantic salmon from Tasmania and Victoria, marketed as both fresh and value-added products, are proving popular and have become very competitive.
For further information call NSW DPI, Port Stephens Fisheries Centre on 02 4916 3900.
Roberts, R. J. and Shepherd, C. J. 1974. Handbook of trout and salmon diseases. Fishing News Books.
Stevenson, J. P. 1980, Trout farming manual. Fishing News Books.