DietSilver perch are omnivorous and in the wild will consume crustaceans, aquatic insects, molluscs, earthworms and plants. The tendency of this species to feed on crustaceans, particularly native freshwater crayfish species such as gilgies, koonacs and marron, is one of the major reasons for strict controls on the distribution of this species in WA. In farm dams, the silver perch diet is mainly comprised of naturally-occurring zooplankton, aquatic insects, freshwater crayfish and algae. Initial nutrition experiments indicate that optimum protein levels for the growout of silver perch are between 32 and 36 per cent as opposed to 50 per cent required by most carnivorous fish (Allan & Rowland, 1991). The lower protein requirement is one factor in favour of this species as a candidate for aquaculture, as the artificial feed costs would be less than those to raise carnivorous species. Recent research in ponds at the Grafton Research Centre has shown that a least-cost diet (35 per cent protein) containing meat meal and plant proteins and only five per cent fish meal was not only suitable for growing silver perch to market size but sustained faster growth than a reference diet containing 27 per cent fish meal. The least-cost diet's ingredient cost, to produce 1 kg of silver perch, was only $1.09 in ponds yielding 6.5 t/ha at growth rates of 2.5 g/fish/day and survival rates of 97 per cent for 440 g fish at harvest (Allan & Rowland, 1998). This trial demonstrates the potential for farming silver perch with impressive efficiency (FCR was 1.9:1). The diet contained a combined total of canola, field pea and dehulled lupin meals, of more than 22 per cent. These protein sources are produced in large quantities in WA and there is potential to produce cost-efficient silver perch feeds in this State. Husbandry & Health Status The major diseases of silver perch are well known and have been reported by Rowland & Ingram (1991) and Callinan & Rowland (1995). These include the usual and ubiquitous freshwater pathogens such as Ichthyophthiriasis multifiliis (white spot), Chilodonella hexasticha and Lernaea (anchor worm). The first of these is a major fish health risk and can be treated with combinations of formalin and malachite green (Thorne, 1995). The Department of Fisheries Management Paper No. 145 titled The Aquaculture of non-endemic species in Western Australia - Silver Perch (Bidyanus bidyanus) contains the disease testing protocol required for the introduction of silver perch into WA. Significant pathogens associated with the introduction of silver perch are the viral disease Epizootic Haematopoietic Necrosis (EHN) and the bacterium Aeromonas salmonicida , which causes Goldfish Ulcer Disease. EHN has not been detected in silver perch, although experimental data suggests that silver perch are highly susceptible to the virus (Langdon, 1989). To date, EHN has not been detected in WA in any fish species. In 1992, A. salmonicida was isolated from skin lesions on silver perch that were held in contact with goldfish known to be infected with the bacterium (Callinan & Rowland, 1995). A. salmonicida has been detected in aquarium fish in WA and there is limited evidence the disease is in feral carp populations. Although the bacteria may be already established in the State, it would not be beneficial to a silver perch industry if infected fish were introduced. All introductions of silver perch into WA will be either quarantined or certified as disease-free and only permitted into impounded waters. |