The paths into aquaculture are many: Andrew Grant started his journey back in 2008 when he built a 660m2 yabby (Cherax destructor) breeding and rearing facility at Bangholme in Melbourne’s southeastern green belt. After the freshwater crayfish enterprise proved un-economical, he switched to finfish – barramundi (Lates calcarifer) – and the farm hasn’t looked back.
At the outset Andrew spent a year or so establishing breeding lines from over a dozen strains of wild yabbies before he moved into the grow-out phase. It was there that the enterprise faltered.
“Our best growers were also the most aggressive,” said Andrew. “We were getting them up to 100g in six months but cannibalism became an issue when the yabbies moulted. We changed our breeding lines to produce more docile animals but then our growth rates dropped off. The Millennium Drought (1995-2012) saved our bacon. I reckon we filled half the swimming pools in Melbourne from our bore [well]. When the drought ended, the change to finfish was a no brainer.”
Initially they tried to use the system developed for the yabbies to grow barramundi, but after a few setbacks Andrew knew the whole facility would have to be reconfigured. The yabby hatchery and growout tanks were replaced with four 80m3 raceways. The first contains the six nursery cages, the other three are the growout tanks, which in turn are divided into three compartments each.
Water is from the bore, which is licensed for 49 million litres annual extraction. Iron levels (4ppm)
are above optimum; pH is 8.0. The high carbonate levels buffer the water against pH crashes, however, Andrew said the bio-filtration “chews through the carbonate hardness… It can be replaced by increasing the water exchange from the bore, but then that [water] has to be heated. We’ve figured that it’s more economic to dose the system with sodium bicarbonate. (We go through about 50kg/month).” Ferrous iron is oxidised by spraying the water into a tank that is gently aerated with ceramic air-stones. The resulting iron hydroxide is removed through sand filtration. The water is then chlorinated and de-chlorinated before it is stored in 23m3 fibreglass tanks. Enough treated water is held to resupply the whole system in 24 hours. Daily water exchange ranges from 5% to 10%. The water is recycled through the filtration system every 90 minutes.
Water flow in the raceways creates a double turbulence: Dr. Tom Lorsordo of North Carolina State University introduced the concept to Australia on one of his winter visits Down Under. Water movement is primarily from the centre of the raceways to the exit point at the other end where it enters the water treatment system. At the same time, water from the fluidised bio-filter is returned to the raceways through jets along the raceways’ rims. Also at the same time water is aerated by airlines placed horizontally 1.2m below the raceways’ surface along their length. This creates a “barrel roll” effect ensuring that there are no dead pockets in the system and that all the organic solids are kept in suspension. It creates a constant water movement and Andrew commented that he’s had positive feedback from his restaurant clients on how firmly muscled their fish are.
Organic solids in suspension are removed in two stages. Water leaving the tanks goes into a multi cyclone where it is slowed in a vortex action so that the heavier particles settle from the water column. From there it passes through two 1.2m diameter spherical filters holding 3.5mm glass beads where the finer particles are collected and back-flushed, The second of those two cylinders Andrew regards as more bio-filter than water scrubber – but it would be fair to say the cylinders are there to give the water a final polish before it goes into the fluid bed bio-filters. Each raceway is serviced by four filters and two pumps; should one pump fail the other maintains water flow and treatment. From the bead filters the water is pumped into the fluid bed bio-filters.
Bio-filtration begins in earnest in the 3m x 3m x 1.8m deep fluid bed filters at the ends of the four
raceways which are divided into two compartments. Water treatment is thus in two stages. In the first, water is sprayed into the bio-filter compartment and then drawn off to the second stage from the top. In the second stage the water enters the growout raceways from the bottom. Each compartment has up to 8m3 of bio-filter media (1.25 million wagon wheels per cubic meter) and that each cube will neutralize 10kg of feed a day. They currently feed up to 40kg/day/tank with oxygen being the limiting factor.
One of the growout raceways has been fitted with, what Andrew has been assured by the US manufacturer, is one of the biggest foam fractionators in the Southern Hemisphere. Driven by a 3hp (2.25kW) pump, the water in the raceway is cycled through the protein skimmer every 40 minutes. Ozone is also introduced through the skimmer. It has increased the feeding capacity on that particular raceway by 10kg. The debate at the moment is between fitting the other raceways with foam fractionation or introducing oxygen injection to the farm. They already deliver atmospheric air through the air tubes positioned along the sides of the raceways.
While the fish in the nursery raceway cages don’t have the same feed requirement as larger fish, they have a much higher metabolism and their bio-chemical oxygen- and water-treatment demands are given the utmost respect. They are, in fact, the fastest growers on the farm.
A reverse cycle heater heats the shed, and the air is a constant 27.5ºC and the water 26.5-27ºC. The air runs at 100% humidity.
The barra fry come from West Beach Aquaculture in South Australia. They are stocked into the nursery cages at 20-25mm, and are fed an INVE diet. Grading is constant during the nursery stage. They weigh less than a gram when they’re stocked and are graded six times in three months. The need to grade drops off as growth rate slows and, due to the previous heavy grading, they grow more evenly. They are moved into the raceways at 50g and switched to a low phosphate Skretting ration which results in larger and more solid faeces.
Ryan Burniston, Farm Manager at Melbourne Barra, said, “The better binding of the faeces gave a noticeable and immediate improvement on water quality. FCRs remained in the same range (1.2:1 to 1.4:), so it was a win all around. The fish take another three months to reach 500g plus, in which time they’re graded three more times at 130g, 300g and 500g.” Overall it takes six to eight months to reach the minimum market size of >500g.
Live fish restaurants
More and more restaurants in Australia now carry live fish. The farm produces up to 50t of barramundi annually and distributes through the south and south eastern areas of Melbourne, but with business increasing Andrew is looking to double his capacity and include a marine-species holding facility. A move into marine species would be relatively simple and would boost his market profile. He would like to grow Murray cod, and breeding his own barramundi remains an option. However, the most immediate enhancement he and Ryan are considering is to install a liquid oxygen silo and oxygen cones to maintain DO levels at 100% saturation or better.
His stint at delivering water taught Andrew the importance of customer relations. When he went into barramundi he based his marketing on reliability and service. One thing he learnt early on during his marketing was that his customers preferred to order all their freshwater fish from one supplier. He was able to source Murray cod (Maccullochella peelii peelii), silver perch (Bidyanus bidyanus) and eels (Anguilla australis) to broaden his catalogue. Melbourne Barra is a clear example of what a small enterprise can achieve through innovation and a flexible approach to the changes that are always present in aquaculture.
— John Mosig
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