Olives are part of the Trevethan's diversification programme
Over-wintering SILVERS T
BY JOHN MOSIG
Paul and Joan Trevethan look forward to higher production from their investment in facilities to over winter silver perch
he silver perch (Bidyanus bidyanus) fi rst gained a foothold in the numerous live and wet fi sh markets set up by migrants groups in the 1990s, and has since promised to
be the next breakout species in Australia. An excellent white fl eshed freshwater fi sh with a distinctive
fl avour, they have battled with production costs that restrict them to a medium value niche market. One of the biggest limiting factors faced by the sector has been the undomesticated nature of the available seedstock. A warmwater native of the Murray Darling system, silver perch has an optimum temperature range of 20˚C to 28˚C and seedstock is only available over the natural breeding season of around three months. Further to that, growth rates of the relatively unselected silvers have seen a bell curve with a longish tail and a fair smattering of shooters. This has seen growers having to grade more than they'd like to, and having to carry slow growing stock over an extra winter. Growers Paul and Joan Trevethan at Howlong in New South
Wale's Eastern Riverina started farming silvers nine years ago. They recognised the problem, and now that the market, albeit a niche, is growing they have made a signifi cant investment in reducing costs by bringing fi sh to the market 12 months earlier by over-wintering fi ngerlings in a temperature controlled recirculation system. The scale of the investment certainly suggests confi dence in the species as a worthy aquaculture candidate. The farm consists of eight 0.4ha ponds holding
approximately 3.5ML each. The stock are protected by total exclusion bird netting. The netting is set above the ponds with suffi cient clearance to carry out feeding, harvesting and pond maintenance operations. Water levels are maintained at 150mm by internal standpipes. The outgoing water from the bottom draining ponds is picked up and channelled to the recycling reservoir from where it can be used on the 10ha of olives or irrigated pasture that make up the farm's diversifi cation program. Each pond has two four-paddle 1kW three-phase aerators.
6 ■ NZ AQUACULTURE ■ MAY/JUNE 2012
