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reached 40mm before Christmas. Nick brings them in to the shed, acclimatises them, then weans them on to a dry feed, allowing him to grow them up to 60mm. The cod grow rapidly at this age and it only takes another three to four weeks to reach the size at which he feels they large enough to fend for themselves when re-stocked in open waters. Once the cod are weaned they are fed at a rate of 3.5 percent body weight a day in total. A close check is done on the cod to watch for any large size variations and then they are graded. This normally happens every two weeks. The main outlet is for re-stocking groups. However, Nick said when they were told by Fisheries not to stock any more cod because they were already well established in rivers, it left him with a few over. So he supplied a local commercial grower who commented that they were the best cod he'd ever taken delivery of. "I put a fair bit of growth and condition on them for the re-stockers and they were a bit ahead of the normal seedstock size he'd been used to getting. They'd had a good run in the ponds, I hold them for around eight weeks anyway," Nick said. "I'd had these in for a bit and weaned them onto dry food. They were graded and were between 3.5g and 4g." Once the cod have fi nished spawning, Nick turns his attention to the golden perch. He'll do two or three spawns, which will also be ready to harvest early in the New Year. There isn't a large demand for silver perch, so he leaves them till last – around late February or early March. He starts checking the golden perch for ova development and spermatozoa motility once the water reaches 21 degrees celsius. This is generally around the end of October. The broodstock are gill netted or angled from the ponds and sedated. The ova and the spermatozoa are checked under the microscope. Once the breeding teams have been selected for their viability, one female to two males, the females are injected with 1000iu of Chorulon and the males 500iu and placed in 1600L spawning tanks at 24 degrees celsius. Spawning commences in 24 to 27 hours and the semi pelagic eggs hatch in 24 to 36 hours. Their mouths will be active in another three days and the larvae are ready to be stocked in the plankton ponds. The females produce approximately 100,000 eggs per kilo of body weight. The plankton ponds are prepared in the same way as for the cod except the timing is more crucial. The fertilised ponds are fl ooded when the spawn has proven successful and the plankton is not as advanced. They are stocked at 100 larvae per square metre. The 5mm long larvae are far more vulnerable than the cod and the food requirement is much smaller. The nauplii of copepods, claudoceran and rotifers are the fi rst feed zooplankton of preference. Survival can be unpredictable. An adverse turn in the weather can send plankton blooms crashing, but after over 25 years in the job the Donges have a good feel for plankton production. While the water itself is healthy, Nick still has to regularly check for parasites. Both the cod and the perch are vulnerable to Trichodina, and the cod are also vulnerable to Chilodonella. He samples the fi sh every three days, and if any infestation appears imminent the pond is treated with formalin. He doses the ponds at the rate of 25ppm and uses power taken off the universal of the tractor to drive the mixer, which also helps maintain the dissolved oxygen levels. Harvesting of the golden perch follows the cod harvest in mid to late January. Nick usually produces around 350K to 400K golden perch a year. Last year, with 450,000 tails, was a record crop. Being over 800m above sea level, once the days start to get shorter the nights cool down quickly. By the end of April Aerial view of the farm taken in 1997 pond temperatures are below 20 degrees celsius and Nick likes to have all the fi ngerlings out of the ponds by the start of April. Markets are mainly to Queensland re-stocking groups, who receive a dollar for dollar incentive to do this from anglers' license fees. There are also a few sales to farmers wishing to stock their dams. Nick said the market was competitive. The recent prolonged drought left some hatcheries without water and farm dam sales had literally dried up. Now that the rains have come back, and although the farm dams need to be re-stocked, every hatchery also has plenty of water and production is at an all time high as producers try to make up for the times they were out of production. Nick Donges can be contacted by phone on 0061 7 4683 5242, and by email on gbfh@halenet.com.au Nick demonstrates how the nesting boxes work The farm-built drum filter The farm-built air pump designed by Jeff Donges SEPTEMBER/OCTOBER 2012 ■ NZ AQUACULTURE ■ 9