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Silver perch Bidyanus bidyanus, is a freshwater finfish species exotic to Western Australia, and has been imported into this State since 1950 for the purpose of stocking inland farm dams . Imports have only been allowed under licence, subject to disease-free certification and on the basis that the fish were being placed into impounded or confined waters. Lawrence (1995) discussed the prospects for aquaculture of silver perch in Western Australia and since then the industry has only expanded slowly. A similar pattern existed in the early days of the silver perch industry in NSW, where rapid progress is now being made, and this species should still be regarded as having significant potential in WA. However, its limited salinity tolerance may restrict its usage for highly saline inland waters. This publication updates the information provided by Lawrence (1995).
Research into the hatchery production of silver perch commenced in New South Wales more than 20 years ago at the Narrandera Fisheries Centre. Since 1990, silver perch has received increasing attention as a candidate finfish species for aquaculture in NSW, Queensland and WA. In 1994, a silver perch hatchery began operation in Parkerville, WA. Silver perch fingerlings are now produced at several farms and on-grown commercially at a number of locations including Northampton, Jurien, Pemberton, Esperance, Dandaragan, Dardanup and the Perth metropolitan area.
Silver perch is native to the extensive Murray-Darling river system of south-eastern Australia. Significant populations, with patchy distributions, of silver perch are found in NSW and southern Queensland. Silver perch also occurs in small numbers in the colder regions of Victoria. Over the past 50 years, the distribution and abundance of silver perch has decreased (dramatically in the last ten years) with silver perch given the conservation status of 'potentially threatened' (Jackson, 1994) and it is possible that the species will become 'endangered' in the future (Rowland & Bryant, 1995).
Although silver perch is not native to WA, it has been brought here for both recreational and aquaculture ventures. Further distribution of this species within WA however, raises a number of important issues relating to the transfer of fish to waters outside their natural or previous distribution (called 'translocation'). These include the potential of the species to establish feral populations in the wild and to introduce disease. As a result the Department of Fisheries has developed a policy to enable the continued development of a silver perch industry in WA in an environmentally acceptable manner. The Department of Fisheries Management Paper No. 107 outlines areas within the State where silver perch may or may not be farmed and how silver perch can be sold or imported into WA.
The areas in which silver perch are permitted are determined by the conservation value of drainage basins:
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Category 1: Drainage
basins, or areas within drainage basins in which silver perch farms and
stocking are not permitted;
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Category 2: Drainage
basins in which silver perch farms and stocking may be permitted, subject
to conditions; and
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Category 3: Drainage basins in which silver perch farms and stocking will be permitted, unless otherwise indicated by the Executive Director of the Department of Fisheries. |
The appropriate temperature for growing this species in aquaculture is 22oC to 28oC (Rowland, 1995c), indicating most areas below the Tropic of Capricorn would be suited to silver perch farming. This coincides with the current distribution of yabbies in Western Australia
Silver perch in their native east coast habitat live in rivers, lakes and reservoirs, although they are found in waters ranging from static to fast flowing.
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Silver perch is a potamodromous species, meaning it migrates wholly within fresh water lakes and streams. In the wild, adults undertake extensive upstream migrations and require an increase in water level to induce spawning (Cadwallader, 1986). Spawning, usually occurs during the summer floods, when water temperatures are above 20oC and inundated flood plains provide juvenile nursery areas (Allen, 1989).
Female silver perch reach sexual maturity at three or four years of age and approximately 340 mm in length, while males mature at two or three years of age and approximately 233 mm in length. There is no sexual dimorphism within the species except for a slight difference in body contour in near-ripe females (Lake, 1968).
Spawning behaviour is very aggressive and injuries such as scale loss and frayed fins are sustained by both males and females. Female silver perch usually release most of their eggs in a single spawning. Water-hardened silver perch eggs are between 2.5 to 3.0 mm in diameter, are non-adhesive and slightly negatively buoyant (Thurstan & Rowland, 1995).
Silver perch can tolerate relatively poor water quality, such as dissolved oxygen down to 2.2 mg/L; pH up to 10.2; and un-ionised ammonia up to 0.7 mg/L, although long-term exposure to un-ionised ammonia concentrations above 0.1 mg/L may adversely affect growth (Rowland, 1995c). Silver perch tolerate long-term exposure to salinities up to 5 parts per thousand (ppt) (Rowland & Bryant, 1995). However, Guo et al. (1995) showed that if acclimated correctly, silver perch are able to survive in salinities up to 12 ppt but die within 18 hours in salinities of 15 ppt or higher.
The growing of silver perch to market size involves three distinct phases (Rowland, 1995b):
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Hatchery Phase: Most growers will not be involved with this phase. It lasts roughly eight weeks, involves collection and spawning of brood fish, incubation of eggs, and rearing of larvae through to fry (30 mm total length or 0.5 g). |
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Fingerling Phase: Fry are grown in farmers' ponds until they are about 15 to 20 g (three to four months at summer temperatures), when they should be harvested and graded. Grading is particularly important, as research has shown that fingerling size is hugely variable from 2 to 50 grams total length after just three to four months. |
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Growout Phase: Graded fingerlings are stocked in ponds for growout to market size (10 to 15 months). |
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| Figure 1: Flow chart showing production phases for the pond culture of silver perch (Source: Rowland, in The New Rural Industries - A Handbook for Farmers and Investors, RIRDC 1998). |
© Copyright 1999-2001 Department of Fisheries.
