GrowthSilver perch may grow to a maximum size of 8 kg and there is evidence that wild fish have a significantly slower growth rate than farmed fish. Growth rates in culture produce fish weighing 500 g in 15 to 18 months (for fish grown in farm dams without fertilisation or supplementary feeding). The optimum temperature for growth of silver perch is not known precisely but is in the range 20 o -30 o C (Rowland, 1998) so it is particularly suited to warm, temperate Australia. The data from Rowland et al. (1995) indicate a marked difference in growth rate between winter and summer months due to reduced feeding; there is negligible growth of silver perch at temperatures below 12 o C. The influence of winter temperatures and latitude upon annual growing cycles must therefore be considered when preparing production estimates and site selection for production in WA. Post-Harvest Handling It is critical to purge and ensure gut evacuation of silver perch before sale to ensure product quality is maintained. Silver perch (and other freshwater fish) can often have a 'muddy' flavour if not purged correctly. This 'off' flavour is caused by compounds produced by blue-green algae and a group of common bacteria called actinomycetes. The compounds are rapidly absorbed by the fish and stored in fat deposits. Silver perch should be purged for three to four days at a salinity of 5 ppt and stocking density of around 20 kgm 3 (Rowland, 1997) although some farmers purge for longer periods (Rowland, 1998). Results from taste panel trials are provided by Allan & Rowland (1998). Polyculture Polyculture involves farming more than one species in the same enclosure. It can help improve profitability because more than one crop is harvested. In WA, research is being conducted to assess the potential of farming silver perch with crustaceans such as marron. This research has shown that silver perch prey on marron in clear water systems (ponds or tanks) (Whisson, 1996). The level of turbidity in the water is likely to be a major factor affecting predation on marron. As turbidity within a pond is due to a range of factors, including soil particles in suspension or an algal bloom, the level of turbidity varies daily and can be manipulated. Cage culture of silver perch within ponds and tanks is envisaged when fingerlings are more vulnerable to predation, however growth rates of fish are often reduced with this culture method (Whisson, 1995). |