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the third. The 1ha settlement pond sits last in line. Although the yields are low when compared with intensively run ponds, the inputs are commensurately low. Andrew says they can expect 400-500 kilos of market-size silver perch out of each pond after two summer growing seasons. He earns $14 per kilo for live fi sh, which means he can gross up to A$7000 from a pond. Compared to the short- term return from rearing bass or perch larvae to fry, which only ties up the ponds for two or three months, the return from the hatchery operation is more fi nancially rewarding. He is looking at a couple of options. The fi rst is to rear the silver perch fry to 100g fi ngerlings in the ponds, then transfer them to fl oating cages in the aerated redclaw ponds to see if he can grow them to market size after only one season in the growout ponds. The other option is to grow the fi sh right through to market size in the fl oating cages. As the buyer likes to collect 200 kilos of fi sh at a time, if they could have, say, 200 fi sh in a cage, they could harvest one or two cages without much trouble and fi ll the transport tank for a quick turn-around, says Andrew. The property is ideal for producing Australian bass (Macquaria novemaculeata). Being only a short distance from the ocean, it's a simple matter to tank in marine water. The females are injected with 1000iu per kilo of HCG in full marine water (35ppt) at 20˚ Celsius. Andrew allows an ovulation period of 30 hours before stripping the eggs into a bowl and mixing in the motile milt of the males. The males are not injected. "I haven't had much success with spontaneous spawning. I'm not sure what it is, whether the males don't go off or what, but our fertility rate spawning manually is well over 90 percent," he says. The bass, possibly betraying their marine origins, are extremely fecund. Andrew estimates he gets from 300,000 to half a million eggs per kilo, depending on the condition of the fi sh. Incubation takes 36-38 hours. Andrew says he can tell within 24 hours if the spawn is going to be any good. "If you can see backbones in the eggs (under the microscope) after 24 hours, you know if you're going to get larvae." The larvae are held in salt water for 21 days, after which time they are suffi ciently developed to osmoregulate in fresh water. They are fed rotifers and brine shrimp sieved down to 200µm during this stage. Andrew will harvest zooplankton from the ponds to keep up a healthy supply of food to the ravenous larvae. Both the artemia and the rotifers are enriched with IS Selco® HUFA fatty acid and amino acid mix before they are fed out. He feels that even if the freshwater zooplankton only last for 15 minutes, the larvae get nourishment from them. Artemia production is straightforward. The salt water is pumped up from the creek on a high tide. "I belt it with chlorine, aerate the chlorine out of it and let it sit for a couple of days." After three weeks the larvae have morphed and are 10-15mm long. They are stocked in ponds that have been fertilised and fl ooded three or four days prior to stocking. Yellowbelly are also injected at the Beerburrum farm and the hatched larvae are taken out to Murgon, about three hours away by road. They are stocked in freshly fl ooded and fertilised ponds. They also raise the Murray cod out there. The cod eggs are collected from shade cloth mesh in nesting boxes made from 44-gallon drums with the ends cut out of them and placed in broodstock ponds. When they are brought into the hatchery, the adhesive eggs are given a one percent formalin bath daily to keep the fungus at bay. The egg screens are hung vertically Andrew inspects 16-day-old bass fry before they are stocked in the plankton ponds Ready for market. A tray of purged redclaw crayfish PADDLEWHEEL AERATION IN THE PONDS OUT AT MURGON HAS IMPROVED OUR YIELDS MASSIVELY. in the water and the larvae drop off as they hatch, usually in eight to 10 days. Once they have exhausted their yolk sacks they are fed enriched artemia before being stocked in plankton ponds. As the cod are more advanced and have a bigger mouth gape than the perch larvae, the ponds are fl ooded earlier than for the perch to establish a more mature plankton population that includes daphnia, as well as copepods and rotifers. "We sell a lot to the farm dam people. We can charge more because there's a lot more servicing in getting them to airports and transport depots. Small sales make up more than half the farm's income. One client in South Australia bought $300 worth of fi sh and the airfreight cost another $500. They paid it without batting an eyelid." Andrew says the industry can only get bigger. "We're going to have to grow more seafood. "In our case we need more aeration. Paddlewheel aeration in the ponds out at Murgon has improved our yields massively. Just turning the water over, getting good algal blooms and breaking thermal layers in the ponds – it all makes a huge difference." MARCH/APRIL 2012 ■ NZ AQUACULTURE ■ 7