By John Mosig
The Finlayson family—patriarch Wayne and sons Brad and Shaun—of Bagdad, 40km north of Hobart, Tasmania are building a recirculating aquaculture system to grow-on eels (Anguilla australis) captured in the wild.
By John Mosig
The Finlayson’s story began in 1964 when Wayne’s father was the only person to apply for an eel
fishing license when they were first offered. The fishery followed a checkered path but by the 1990s the Tasmanian government recognized the potential of hundreds of fresh water storage reservoirs and restructured the fishery. Now, with secure license tenure, eel fishing has a solid commercial status and has given Tasmanian Eel Exporters the confidence to invest in its future.
Bigger is better
Already exporting to four countries, the company has realized that the only way to sustainably increase its business is to increase the size of the fish before marketing them. This will improve the condition of the eels and extend production over the whole year.
Eels are sold live, packed in polystyrene boxes—13kg of fish to a litre of water in double-lined plastic bags filled with oxygen. They’re shipped to high-end Chinese restaurants in New York as well as to buyers in China, Japan and South Korea. There is also a domestic following in Sydney.
The company has increased the number of its Tasmanian fishing licenses (reservoirs) and can now comfortably harvest 60t of eels a year. However, adverse conditions such as the recent El Niño saw Tasmania’s water reserves down to 12% of capacity and this can severely restrict eel migration and reduce harvests.
Historic data set
The Finlaysons have a historic data-set of eel catches from all the waters they have fished over the years, which allows them to follow recruitment trends and plan their harvesting schedule. This has streamlined their operation, boosted production, and reduced operational expenses.
The data also help maintain sustainability: they can transfer juvenile eels from overstocked waters to more productive ones, and with the help of Hydro Tasmania, they can capture migrating elvers trapped below power stations and liberate them further upstream. They have noticed that harvesting areas depleted of large fish have enhanced recruitment the following season. This reduces the number of market-sized eels in the catch, but provides more fish for the grow-out facility.
The harvest weight of wild eels varies, as does their condition. Shaun Finlayson pointed out that putting them through the RAS farm will ensure that every eel sold will be in prime condition, meriting a premium price. Currently they sell three sizes: 1kg+; 600-999g; and 300-599g. It is envisaged that the third grading, (small, poor quality fish) will no longer be offered, and that they’ll be able to lift all sizes to premium grade.
Fish are captured in fyke (trap- or hoop-) nets that are very portable and easy to re-set wherever the fish are running. The fishing season normally runs from September to May. Shaun noted that the first decent cold snap stops eel movement in its tracks. Breaking the recent drought and the unseasonably warm temperatures last winter had seen the eels moving until the end of June.
“Stock management is something we’re working on,” Shaun says. “We’ve got 30 tonnes of holding capacity now, and with the new farm we’ll be able to hold and fatten another 30 tonnes. A lot of what we’re doing hasn’t been done before on this scale, and in many respects we’ll be pushing the boundaries of what little information is on hand.”
RAS makes it possible
The grow-out farm was designed and installed by Fresh By Design (FBD): one of Australia’s most innovative RAS construction companies. Chief Designer, Lindsay Hopper, was enthusiastic: “At Fresh By Design we are often tasked with the unusual, so when the Finlayson family came to us with their plan/dream for an eel grow-out facility we were instantly excited. It will be the only one like this possibly anywhere in the world and to be involved from conception through to commissioning is a truly motivating experience.”
The insulated building is temperature-controlled via the combination of a 21.8kW Oasis Heat Pump and air conditioning system ducted through the room to control humidity.
There are twenty 9m3 poly culture tanks, with a filtration system designed around a peak feeding rate of 525 kg/day. Water is pumped into the tanks through four 960watt Emperor Aquatics U.V. Sterilizers, then through an oxygen cone (FBD Model 1) on each tank.
Oxygenation can be matched to the demand at peak eel biomass, which could exceed 150kg/m3
stocking density. Water leaving the tanks is gravity-fed via specifically engineered floor channeling, to a Faivre 16/120 On-Frame Drum Filter fitted with 36µm screens, and then through a Moving Bed Bioreactor (MBBR) and bioblock degassing unit into the sump.
The MBBR contains 40m3 of FBD’s C1 NitroBio Filtration Media, which has a specific surface area of 800m2/m3. FBD has recently introduced this new improved media which, being black in colour, results in increased nitrification performance. In order to get to peak stocking density rapidly, FBD’s special biological inoculum blend, Bio-One, & Nitrospira MKII, are now part of the startup and conditioning process.
Aeration & Filtration
Two 7.5kW side channel blowers are plumbed in a duty/standby configuration that provides aeration and circulation to the MBBR. Up to 563,000 l/h is processed through the MBBR, and pumps returning water to the tanks achieve a water exchange every 24 minutes. Additional filtration is provided by an RK600PE Freshwater Protein Fractionator, to which ozone (model RK2, 15g/hr) is added to enhance water quality control. Further control over dissolved solids (TDS) is ensured by the inclusion of an AST (Aquaculture System Technologies) Propeller-wash Bead Filter, with an automatic backwash control system. A local farmer is ready to take the solid waste material for soil conditioning.
Pumps and Feed
Australian designed and manufactured Paterson Turbine pumps were chosen for their energy
efficiency, serviceability and reliability. They also negate any concerns over nitrogen super-saturation given their submersed design.
Oxygen from a bulk supply is delivered to the oxygen cones at rates up to 10 l/min, and, via a back-up emergency delivery system, to Colorite oxygen rings in the tanks.
Feed is delivered automatically over 24 hours at 1-3% of biomass per day, depending on the appetite of the particular batch of fish. In the absence of a species-specific eel diet, they’re using Skretting’s salmon rations. Expected FCR is 1.3:1. From some preliminary trials they’ve carried out, time in the “fattening” tanks will be 7-12 weeks.
Eel marketing plan
The basic plan is to sell all wild-caught eels that weigh over a kilo, and on-grow the others in the RAS. According to Wayne, feeding them under controlled conditions to produce bigger and better quality eels has many positives and very few negatives. Management of the wild fishery will continue as before to keep the farm fully stocked.
The economics are that even at an FCR of 2:1, the new facility, once fully operational, has the capacity to produce 260kg of eels daily; product that would otherwise not be available. That translates to nearly 100 t/year of premium quality eel, almost a 160% increase in output. At an FCR of 1.5:1—a realistic target—production from the wild fishery and the farm has the potential to reach 330 tonnes per annum.
The learning curve will be steep, but it will be upwards. The Finlaysons admit that it’s a leap of faith, but are confident that they can navigate the path from hunter-gatherers to farmers. They have three generations, and a half century of hard-won experience and data to draw from, and the incentives are lucrative.
For more information contact: email@example.com.
— John Mosig