Rural Industries Research & Development Corporation

The New Rural Industries
A handbook for Farmers and Investors

Trout

Introduction

The land-based farming of salmonid fishes in Australia has a relatively long history, dating back to 1864 when fertilised eggs of brown trout, Salmo trutta, were imported from England. Several other salmonid species including rainbow trout, Oncorhynchus mykiss, Atlantic salmon, Salmo salar, brook trout, Salvelinus fontinalis, and chinook salmon, O. tshawytscha, have since also been introduced from the northern hemisphere and are being farmed to varying degrees at government and private hatcheries in NSW, Victoria, Tasmania, South Australia and Western Australia.

Of the trout species being farmed, rainbow trout and brown trout are the most common. Brown trout are produced primarily for state-based stock enhancement programs, which form an integral part of freshwater recreational fisheries management in the cooler, upland catchments of NSW, Victoria and Tasmania. Rainbow trout are produced on a far bigger scale for human consumption, and to a lesser extent for recreational purposes, including stock enhancement of public and private waters and on-farm `fish-out' operations.

Most land-based trout farms are on private property close to a natural waterway from which water is diverted through the farm before being discharged as effluent back into the same waterway. The matters of water diversion and effluent discharge are currently the subject of considerable debate between the commercial trout-farming industry and various state fisheries, water management bodies and environment protection authorities. Restrictions on water diversion and effluent discharge are regarded by the industry to be an impediment on increased production.

Environmental legislation in many states now prevents the discharge of aquatic effluent from some types of fish farms (e.g. native fish farms in NSW) back into the environment, or at least stipulates that effluent water quality has to be at least as good as that of the in-flow. Key parameters used to monitor water quality effluent include total nitrogen, total phosphorus, Biological Oxygen Demand, pH, dissolved oxygen, suspended solids and temperature.

Markets and marketing issues

World salmonid aquaculture production, including land-based and sea production of trout and salmon, is about 717,000 t and worth approximately US$3.1 billion/year. Rainbow trout (mostly land-based) makes up about 43% by volume (t) and 34% by value of total world salmonid production (1993 estimates). The major trout-producing countries are the United Kingdom, Italy, Spain, France, Germany, Chile, Denmark and the USA. Land-based trout farming production in countries such as Spain and Italy is currently increasing at about 10% per annum.

The major aquaculture production of salmonids in Australia occurs in Tasmanian sea cages, with approximately 6,192 t of Atlantic salmon and approximately 490 t of rainbow trout (ocean trout) per annum worth over AUS$56 million and AUS$3.9 million respectively (1994/95 estimates). However, land-based trout farming is the biggest freshwater sector and second biggest finfish sector in the Australian aquaculture industry with about 2,000 t worth almost AUS$12.5 million (of mostly rainbow trout) produced annually (1994-95 estimates).

The upper table below (not available in this html version) summarises the number and estimates of annual production (1994-95, unless otherwise stated) of rainbow and brown trout for each state.

The range of existing Australian land-based farmed trout products, together with nominal/estimated wholesale unit prices (delivered) is shown in the lower table below (not available in this html version).

Marketable sizes range from the smallest (entrée size) whole fish, approximately 210 g weight, to the largest fish at about 3.0 kg in weight. The most common size is 300-400 g for whole fish and about 100-200 g/portion for fillets.

The wholesale/retail network for farmed trout usually involves the sale of the product by the farmer to a wholesaler, the fish market or to frozen food distributors, and then to retailers such as restaurants, supermarkets, and fish shops.

Hatchery production of juvenile fish (fry and yearlings) for recreational fish stocking in public and private waters is primarily carried out by government-owned hatcheries or by private hatcheries under contract to state governments. A number of hatcheries also sell fish direct to the public for stocking farm dams and also for stocking private waters for commercial `fish-out' operations. Brown trout are mostly favoured for stocking flowing waters and rainbows for lakes, impoundments and farm dams.

Production requirements

Maintenance of optimal water quality, temperature and flow rates are critical to reducing stress on farmed fish and to achieving maximum growth and survival. Farmed trout require relatively large quantities of fresh, flowing, highly oxygenated water at temperatures ranging from a minimum of 5 to10°C to a maximum of 15 to 20°C (optimal 8-18°C). Dissolved oxygen levels in excess of 5 mg/L and temperatures between 8 and 18°C are preferred at typical commercial stocking densities of 10-20 kg fish/m³ of water. Flow rates, without supplementary aeration and assuming dissolved oxygen levels at or near saturation (>80% saturation), should be about 510 L water/second/t of fish.

Most farms operate a completely flow-through, single-pass system. In most cases the water supply is an adjacent stream which is diverted by gravity or pumped through the farm, with effluent being discharged back into the waterway downstream of the diversion point. In many farms, effluent is directed through a terminal, non-production pond with a relatively large surface-area-to-volume ratio, which enables some settlement of suspended solids (residual fish food, faeces and other wastes) before the effluent is discharged. During periods of low ambient flows in the supply stream, some re-use of water is achieved by pumping waste-water back into the supply.

To meet environmental concerns, farmers are now having to consider the implementation of some form of additional treatment of effluent to reduce the levels of suspended solids, nitrogen and phosphorus. Options include the retrofitting of settlement ponds and/or constructed wetlands (if not already present), mechanical removal of suspended solids through the use of rotating micro-screen drum filtration, and supplementary oxygenation of ponds, tanks and raceways through the use of mechanical aerators and oxygen generators.

To what extent any or all of these options are efficient, practical and cost-effective remains to be seen. Of recent years, the quality of locally produced trout feeds has improved substantially, with less waste and increased FCRs. Current trends in trout-feed manufacturing, largely reflecting industry needs, are towards higher energy diets with lower phosphorus levels to increase cost-effective production and reduce environmental impact.

Holding and rearing facilities vary from farm to farm, including fibreglass, concrete and prefabricated swimming- pool tanks and concrete and/or earthen raceways and ponds. The most favoured grow-out facility consists of relatively small
(0.05-0.1 ha surface area; 1.02.0 m deep) earthen ponds or raceways with concrete inlet and outlet structures. Netting over the ponds or raceways is sometimes used to keep birds off.

The requirements for fish-farming permits and associated costs, including for land-based trout farming, vary from state to state but generally include:

• local government planning approval and public health approval for processing facilities (if appropriate);

• AQIS approval for export facility;

• water supply diversion permit from relevant water authority (if accessing public waters);

• effluent discharge permit from relevant environment protection agency (if discharging back to public waters); and

• fish culture permit (allows commercial trading in aquaculture produce).

Varieties/breeds

Many farms maintain their own captive trout broodstock to supply their own or other farms, although some farms also collect `wild' brown trout broodfish on an annual basis for recreational fishing and stock enhancement purposes. It is unclear whether there are any true, genetically discrete, `wild' strains of trout in Australia, with the possible exception of Tasmania. Most brown and rainbow trout in natural waters in Tasmania are not derived from hatchery progeny but from natural recruitment, and are thought to have been geographically and reproductively isolated from more `domesticated' stocks long enough for them to be considered genetically distinct. Wild strains of trout are particularly favoured for recreational fishing because they are thought to offer better sport.

The domesticated strains of trout used in land-based farming are mostly selected for fast growth and high survival under intensive grow-out conditions. Additionally, a domesticated rainbow trout strain is maintained in Western Australia which is purported to be temperature tolerant, and therefore more suited to warmer ambient climates. More recently the production of various hybrid, all female, and sterile, triploid (artificially induced; three sets of chromosomes) strains of rainbow trout have been developed for commercial farming purposes. These fish typically exhibit better flesh quality and condition, and relatively rapid and/or more prolonged growth to larger sizes than normal strains.

Husbandry

Intensively-farmed trout are fed on commercially available (locally produced), dry pelleted (steam pressed or extruded), compound diets, specially formulated and sized for each production stage (viz., juvenile starter feeds, grow-out and broodstock conditioning). Feeds are distributed daily by hand or with commercially available autofeeders. Feed rations and feeding frequency vary with stocking densities, water temperature and the developmental stage of the fish.

Options for feed rates specifically include feeding to satiation (demand) and feeding according to set weights (as percentage of fish biomass). Australian industry standard Feed Conversion Ratios (FCRs) range between 1.2 and 1.8 (kg food/kg fish weight), and vary with species, developmental stage, feed quality, feeding regime (auto/manual, frequency of feeds etc), water quality and temperature, stocking density etc.

Growth rates for farmed trout vary according to much the same parameters as for FCRs, but on average range between 100 and 300 g after 12 months, 1500 and 2000 g after 2 years and 4000 and 6000 g (mature broodfish) after 3 years.

Spawning occurs annually during May-July for both rainbow and brown trout, with maturation occurring in response to temperature and photoperiod cues. Trout breeding involves the hand-stripping and dry fertilisation of ripe eggs and sperm from 2-4 year old mature fish held on site. Fertilised eggs are incubated in flow-through containers and hatch after approximately 6 to 9 weeks at temperatures of 5 to10°C. On average up to 1000 eggs/kg of fish weight are stripped per female, and survival to hatching is usually up to 80%. Overall survival, from eggs to harvest, is typically in the order of 60-80%. It should be noted that many farms (about 50%) do not maintain broodfish but simply purchase young-of-the year juveniles (e.g. 5 g fingerlings) from other farms for their annual production needs.

Many farms crowd fish at high densities and reduced feed rates to retard, or `stunt' growth, so as to ensure a year-round supply of fish at a specific size to meet market requirements. As required, growth in these fish is enhanced through increased feeding and lowered density to bring them up to market size. Many farms also simply employ the latter strategy, without stunt growing, to `finish fish off' to market size as required. In a typical annual production cycle, most farms need to have the capacity to hold approximately 40% of annual production, including progeny from two year classes.

Pest and disease control

Most disease outbreaks in land-based trout farms are stress-related and caused by poor water quality (e.g. inadequate flows and/or aeration) and/or poor husbandry (e.g. inadequate feeding practices, excessive stocking density), often compounded by high ambient summer temperatures.

The most common disease pathogens are ecto-parasitic protozoa (e.g. Ichthyothirius sp., also known as white spot, and Trichodina sp.) which commonly occur during the months of the year when the water is warmer. Bacterial and viral pathogens are less common, although EHN virus, also known as redfin virus, is a stress-related, water-borne pathogen which has sometimes caused significant mortalities in some NSW and Victorian farms.

In most cases disease outbreaks are controlled by reducing stress levels (eg. through increased flow rates, supplementary aeration, reduced stocking densities etc) and in extreme cases by the use of chemical parasiticides and/or antibiotics. Apart from reducing the rate of infection through reduced stress, there is no therapeutic treatment for EHNV infection of trout.

Harvest and postharvest handling

Trout grown in ponds and raceways are usually harvested by some combination of seine or crowder nets and dip nets. Fish pumps or mechanical lifts are also used, sometimes in combination with electronic counters and/or mechanical graders. Ideally, the select grade harvested fish are then chilled in an ice slurry before immediate processing. Although such quality assurance procedures are not yet standard practice for all farmers, there is increasing pressure to adopt them because of a more discerning marketplace and more stringent regulations with respect to community health.

In general, the normal fresh-food industry and associated government health standards apply. For any value-added processing, such as smoking, specific training is required. For economic reasons, not all trout farms undertake on-site processing and/or value-adding, preferring instead to be contract growers; processing and value-adding being undertaken elsewhere by another operator.

Economics of production

Given that land-based trout farming is a relatively mature industry sector with reasonably orderly markets, production costs are generally considered to be low in comparison with other aquaculture industry sectors/products in Australia. With such narrow profit margins, the industry places a premium on efficiency of production. Consequently, economies of scale dictate larger-volume production for individual businesses to achieve long-term economic viability. Large-volume production is also essential because existing domestic demand is being met by existing local production.

There are opportunities for the export of land-based farmed trout products but market prices would be marginally less than on the Australian domestic market, because of competition from other countries. International competition for farmed salmonid products is relatively severe at the present time because of increased global production and an associated decline in world market prices. Only about 5% of Victoria's total annual production is exported from two AQIS-approved export processing facilities.

Major operating costs include fertilised eggs and/or fingerlings (if purchased), feed, labour, water, energy (particularly if pumping water), insurances, rates, miscellaneous licences, processing, packaging, freight, marketing (advertising), depreciation on capital and interest on borrowing. Major capital costs include ponds, raceways and tanks, broodfish (for hatchery), pumps, production equipment (e.g. graders, fish pumps, scales, counters, and nets), bird netting, security fencing, processing plant and equipment, vehicles, and cold storage facilities. Capital and operating costs typically vary with the species, product type, geographic location and scale of operation.

For a medium to large-sized farm (100-300 t/year production capacity), production costs range from $4-5/kg for conventional, fresh/frozen, gilled and gutted whole fish, up to $15/kg for value-added products, such as smoked fillets.

Key contacts

Key references

Davies, P.E. and McDowall, R.M. (1996). `Salmons, Trouts and Chars'. In: Freshwater Fishes of South-Eastern Australia (ed. R. M. McDowall). Reed Books, Sydney.

Kailola, P.J., Williams, M.J., Stewart, P.C., Reichelt, R.E., McNee, A. and Grieve, C. (1993). Australian Fisheries Resources. Bureau of Resource Sciences, Department of Primary Industries and Energy, and Fisheries Research and Development Corporation. Canberra, Australia.

Piper, R.G., McElwain, I.B., Orme, L E., McCraren, J.P., Fowler, L.G. and Leonard, J R. (1982). Fish Hatchery Management. United States Fish and Wildlife Service, Washington, DC

Shepherd, J. and Bromage, N. (1988). Intensive Fish Farming. BSP Professional Books, Blackwell Scientific Publications Ltd, Oxford, England.

*About the author