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Looking into the new system nearing completion removes suspended solids. Dissolved wastes are removed in a moving bed biofi lter. The biofi lter is set in the ground and holds 20m3 After cleaning, the water is delivered by an Australian made of water. The biomedia are Kaldnes K1 beads. Enough biomedia is added to initially allow around 100 kilos of feed to be introduced daily. This can be lifted to around 140 kilos a day by adding more media. AERATION/OXYGEN The biomedia is aerated as are the growout tanks and sump. Two blowers deliver 1200 litres per minute. One is used as a backup to the other. Each tank (in relationship to the size of the tank), has two, three or four air stones at the base of the central drainage outlet. The aim is to keep the water as near as possible to saturation. Being set 100mm off the bottom they allow waste material to settle and leave the tank with the exchanged water via the bottom drainage slots in the standpipe, rather than it being kept in suspension within the system. The Moving Bed Process® allows the biomedia to self clean as the media rub gently against each other. Removing the exhausted nitrifi cation bacterium encourages new growth. The new fi ltering fi lm is vigorous and helps maintain a robust and self-cleaning biofi ltration system. The biofi lter is fl anked by a sump that acts as a water reserve. Should the pumping system fail, for whatever reason, the spare water storage acts as a buffer for the water in the system's delivery and return lines. There is also a submersed backup pump in the sump should the above ground pumps fail. Water levels in the tanks are controlled. The tanks can be drained to two-thirds of their capacity for ease of harvesting or to treat ailing fi sh. Water temperature is controlled by a Fresh By Toyesi reverse cycle heater/chiller plugged into the delivery line. Operating water temperature is a species-comfortable 24˚C. Both air and water temperature are controlled with passive dehumidifi cation. In the summer Paul joked, they'd probably have the doors open at night to cool the place down. 8 ■ NZ AQUACULTURE ■ MAY/JUNE 2012 axial fl ow pump with capacity to turn the system over twice an hour with less than 3kW of power. Based on the joint experience of the grower and the designer, Ben Pope, the system addresses important aspects for day to day operation such as harvesting, grading, and simple things like plenty of inspection ports in both the pressurised 150mm delivery and the 225mm gravity fed return pipes. This enables the lines to be cleaned to remove fouling build-up. The bio-fi lter can also be bypassed should any treatment be required, particularly treatment with formalin and antibiotics. Paul said it was part of the system's disease control; "If you have thorough hygiene built into the design of the system you could do away with expensive-to-buy and costly-to-run UV and ozone equipment." The design also considers the ergonomics of the system. Every consideration has been given to making the system uncomplicated and cost-effective to use. Things like allowing adequate space to move around the tanks with fi sh handling equipment, and the simplicity of the operation, all make life easier for anyone operating the farm. THE FUTURE Paul has served as the warmwater fi sh farming sector on many occasions in his role as president of the Murray Region Aquaculture and on the executive of the NSW Silver Perch Growers Associations. "The markets are there, " he said. "We have regular wholesalers who will take everything we can push through the purging system. The demand for fi sh is strong. We have been selling for six years now and the buyers know our fi sh. It has given us the confi dence to invest." However, he has some advice for anyone contemplating investing in the silver perch industry; "There are three things to consider. Firstly, you have to have the markets in place. Secondly, you need the experience, and thirdly, be prepared to invest in a quality system. If you put in an ordinary system you're struggling from the start."