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. General Biology 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 20 o C 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. | 