This information comes from "A HANDBOOK FOR FARMERS AND INVESTORS"
 | ABOUT THE AUTHOR Stuart j. Rowlands BA(Hons).PhD has been conducting resurch into the taxonomy, biology and aquaculture of native fishs for over 20 years. He developed techniques for the artifical breeding of murry cod, golden perch and the endangered easten cod, and for the husbandry and intensive pond culture of silver perch |
The silver perch, Bidyanus bidyanus (Mitchell), is an Australian native freshwater fish that is endemic to the Murray Darling river system. It was commonly used as food by Aborigines, but is now uncommon in the wild
Hatchery techniques for silver perch were established by the early 1980s. Research at the NSW Fisheries' Grafton Research Centre since 1990, has demonstrated that silver perch is an excellent species for culture in earthen ponds. High survival (> 90%), fast growth rates
(2-3 g/fish/day) to market-size (cal-l 500 g) at high stocking densities (20,000 fish/ha) lead to high production rates ( lO t/ha/ year), with relatively low feed costs ($I.OO/kg of fish). Silver perch has the potential to form a large industry (> 10,000 t/year) based on high-volume, low-cost production.
The major challenges for the industry are to reduce feeding and production costs, to develop efficient farms using good aquaculture practices, to develop and implement a quality control program and to establish a processing component leading to the supply of silver perch in a consumer-friendly form with an effective marketing campaign.
Silver perch is a premium quality fish, which has a mild flavour, moist, white flesh, with very few bones and a high meat recovery of 40%. Like all freshwater fish, it can develop a 'muddy' taste or 'off' flavour from the pond environment, and so needs to be purged after harvest.
Silver perch are marketed in the live-fish trade, which serves mainly Asian restaurants in Sydney and Brisbane. Prices to the grower are $10-15/kg, and The fish retail for $20-4Slkg. This relatively small but lucrative market is expected to increase as Asian communities in Australia grow, and the demand for high-quality, fresh product increases across our society.
Some farmed silver perch are sent whole and chilled to the Sydney Fish Markets where they can bring $5-l3/kg at auction, depending on presentation, quality and daily market fluctuations. Several farmers are developing local markets in clubs, hotels and restaurants. There appears to be much scope for local marketing in inland regions where silver perch is well known and regarded, and where there is a shortage of fresh fish. Large-scale marketing and promotion of silver perch have not yet been undertaken because of the present limited supply of the fish.
By far the largest market available is the domestic market for processed product eg. Fresh fillets, frozen, and packaged fillets. Much of the fish eaten in Australia is in this category, and most of it is imported. The great potential for development of the silver perch industry is in replacing some of the fish sold through retail outlets, supermarkets, clubs, hotels, plus that provided in institutions such as hospitals, nursing homes, military bases and so on, with farmed silver perch. Processing increases product types, greatly expands market niches, and will enable the clear delineation of farmed fish from wild-caught fish. The latter is important because of the growing consumer concerns about the increasing pollution of estuaries and the marine environment, both in Australia and overseas, and the subsequent effects on the quality of seafood.
The number of farms and the production of silver perch have now reached levels that guarantee increasing availability and continuity of supply. Markets outside the niche live- fish trade can now be developed and the species promoted to a wider range of consumers.
Silver perch is a temperate, warm-water species that can tolerate water temperatures of 2° to 38°C. although it can live over a wide area of Australia, Optimum water temperatures for growth are between 200 and 300C. The length of the growing season, and therefore the time taken to reach market size, will be determined by the temperature regime. Regions with a growing season (> 20°C) of at least 5 months, preferably 7 or 8 months, are most suitable for the commercial aquaculture of silver perch. This excludes much of Victoria and the southern tableland areas of NSW. Successful farms are located from the Murray River to northern Queensland.
Site selection is the first and most critical step in establishing an aquaculture facility. An abundant supply of good quality water is essential. Large, permanent rivers and creeks are most commonly used, and underground water is ideal, assuming the quality is acceptable. If rain run-off is to be used as the main supply, water budget and storage requirements must be closely estimated. Domestic water supplies should be avoided because of the limited supply. High cost and chlorine and ammonia content.
An experimental Freshwater aquaculture facility has been established at the Grafton Research Centre. Water is pumped from the Clarence River to two earthen reservoirs
(Capacity 17.5 ML) from where it is gravity fed to the 19 ponds (15 @ 0.1 ha; 4 @ 0.3 ha) and buildings, effluent water from all facilities drains into an effluent/ settlement dam (43 ML) from where it is r~-used by pumping to the reservoirs or stored for irrigation of pastures and crops. The NSW Fisheries' Silver Perch Aquaculture Policy requires that no effluent water is released to natural waterways.
Ponds should be constructed from impervious soils to eliminate or reduce the loss of water by seepage. Clay or clay- loams are ideal. Ponds should be 0.1 to 0.5 ha surface area, and those larger than 1.0-ha should be rectangular. The bottom should slope evenly to the deep section (2.5 m), which may contain a harvest sump. Each pond should have an inlet and a screened outlet structure, and should be completely drai1lable- by gravity. Banks should be wide enough to ensure strength, stability and vehicular access. Electricity should be available for the aeration of each pond. Fingerling ponds should be netted or covered with wire to prevent perdition by cormorants. A building(s) containing an office, laboratory, quarantine /-purging tanks, equipment and work area is also an essential part of a fish farm.
All research, hatchery production and grow-out of silver perch to date has used the progeny of 'wild' broodfish, originally collected from the Murray- Darling river system. There has been no artificial selection. Recent research has identified several distinct genetic stocks or 'strains' of silver perch. And a selective breeding program is now under way at the Grafton Research Centre using fish from these stocks. These silver perch have been made available to industry for use as future brood-fish
A three-phase production strategy is recommended for the pond culture of silver perch:
I - Hatchery;
II -Fingerling;
III - Grow-out.
This strategy combined with a single-batch system where each pond has only fish of the same age or batch, which are harvested completely before the next batch is stocked. Contributes to good aquaculture practice. The three-phase production strategy, however, is not rigid and there is scope for flexibility to suit each farm according to its facilities and production potential, and to enable continuity of supply to markets.
Some farms are involved in only one or two of the phases. A hatchery is a specialised operation requiring broodfish, spawning and incubation facilities, larval rearing ponds, and a relatively high level of technical expertise. Farmers can either purchase fry from a
hatchery and then use Phases II and ill to rear fingerlings, then market-size fish, or purchase fingerlings only and grow outto500g In cooler regions, where there are relatively short growing seasons, it would be an advantage to stock in early spring, large (50-100g)fingerlings that could be reared to 500g by the end of the growing season in march.
Ponds are prepared by drying, removal of excess organic matter, and in some cases tilling to provide the basis for optimum water quality and fish health. Fish are quarantined in tanks before stocking, to reduce stress and to ensure they are free of disease. Recommended stocking rates are 20,000-100,000 fish/ha in the fingerling phase and 5,OO0--21, 000/ha in the grow-out phase. Grading is necessary after the fingerling phase because a large size-range develops irrespective of stocking density. Silver perch reach a mean weight of ca 500g in 15 months from spawning, and fingerlings (15 g) stocked in may reach 500 g in 10 months. Annual production rates up to 10 tonnes/ha have been achieved in static ponds at the Grafton research Centre. Research to date suggests that although silver perch survive and feed well in cages and tanks, growth rates are slower than fish cultured in ponds.
Silver perch are fed a formulated diet containing 35% protein and made up of meatmeal, field peas, canola, peanut meal and lupins, plus a small amount of imported fish meal. Fingerlings are fed up to 7.5% and larger fish to 3% body weight per day. Food conversion ratios (FCR -weight of food fed: gain in wet weight of fish) of 1-2:1 for fingerlings and 1.5:1 during grow-out are now readily achieved using good quality feeds, appropriate feeding regimes, and by maintaining good water quality and fish health. Nutritional research by NSW Fisheries scientists has resulted in a lowering of the cost of feed from about $1,000 to $750/t the cost of feeding silver perch is now around $l.00/kg of fish. Future improvements in the formulation and quality of diets, and feeding strategies should see a further decrease in the cost of feeding silver perch, hence a lowering of overall production costs.
Fish are sampled monthly form each pond using a seine net, to determine the mean weight, estimate the biomass of fish in the pond and to adjust the daily ration accordingly. Several fish are also examined for disease.
Although silver perch is a hardy spices, successful aquaculture depends on the maintenance of good water quality. Temperature, dessolved oxygen concentration, pH, total ammonia and unionised ammonia are monitored two or three times a week because they can change from acceptable to stressful or lethal levels within several days, particularly in the warmer months. The main techniques used to manage water quality are aeration water exchange, reguiarion of feeding and stocking density, and the drying of ponds between crops. Dessolved oxygen is the most critical variable and aeration of ponds is essential in semi-intensive and intensive aquaculture. Silver perch ponds are aerated for at least 6 hours nightly (0200 0800h) usually with electrically powered paddle wheel aerators at a rate of 6-10 HP/ha.
The diseases of silver perch are well known, and techniques for the diagnosis and treatments have been developed and can be readily implemented on farms. The major ectoparasite diseases and the pathogens are:
white spot, ichthyophthjirus muinpins;
chilodonclliasis, chilodonella hexasticha;
trichodiniasis,trichodina sp,
ichthyobodiasis, ichthyobodo nectator;
Fungral diseases are:
Fungus or cottonwool disease, saprolegnia SP;
Epizootic Ulcerative syndrome (EUS) or red spot, aphonomyces sp.
The major bacterial diseases and pathogens are:
Tail rot, flexibacter sp. And or aeromonas sp.;
Columnar, flexbacter columnaris
Goldfish ulcer disease (gud), acromonas salmonicida.
Rapid diagnosis of most diseases can be made on site using a high powered microscope. The incidence of disease is much lower on well-designed and managed farms. And the following factors contribute to a health management program;
A suitable site with a good water supply and facilities,
Purchase of disease free fish,
Use of quarantine procedures,
Appropriate stocking densities;
close observation of fish during feeding;
Maintenance of good water quality,
Regular disease checks,
Careful harvesting and handling,
And the drying of ponds between crops,
Silver perch are partially harvested using a seine net. Each pond is then drained and the remaining fish concentrated in an internal or external sump. Fish are hand-netted into bins containing water and transported to on-site purging tanks. Mechanical harvesters such as fish pumps and pescalators are used on large farms. Silver perch need to be purged for one to three weeks to eliminate 'off' flavours. Underground, spring or domestic water should be used because surface waters may contain 'off' - flavour compounds. Salt (3-5 g/L) is added to the water to reduce Stress, prevent fungal infection and kill ectoparasites. Fish are not fed during this period. Purging will ensure a high quality, uniform product, and so is essential even for fish not destined for the live market. Silver perch are transported in enclosed fibreglass tanks on trucks. The water is filtered and oxygenated. Although silver perch are now displayed live in many Asian restaurants, they can be killed humanly and rapidly by placing them in ice slurry or by ike jime, in which case they are then packed on ice in polystyrene boxes, labelled and transported to market. As with all seafood, freshness, quality and presentation are vital for successful marketing.
The economics of farming silver perch have not been determined because of the infancy of the industry. Most farms are ether under construction or have only been built in the last three years. Aquaculture is an intensive animal industry that requires substantial capital investment, labour input and operating costs. The profitability of silver perch farming will be sensitive to the stocking densities used, the selling price and the cost of feed. The following figures are based on a business plan, which includes all costs associated with the purchase of land and equipment, and construction of 10ha of ponds. Estimated capital costs are $ 1 million Annual costs (excluding depreciation) are $272000 and $344000 and the minimum selling prices required to achieve 6% returned on investments aer$6.80 and $4.30/kg at annual production leaves of 50 and 80 tonnes respectively. The costs and minimum selling prices will be lower on farms with available land, infrastructure and equipment and in the future as the costs of feed and fingerlings decreases, the advantages of genetic selection, higher stocking densities and improved feeding regimes are implemented, and farms in general become more efficient.
| Frames Page | return to fish index | Site Map |