On dry land
losses because they have never experienced a power failure, and it was the same for my farm – as long as you have emergency gener- ators and oxygen,’ he adds.
SMALL FISH
Rather, he explains it is human or managerial errors that cause the problems in recirculation systems, such as the oxygen supply to a tank being switched off by accident. ‘What most often goes wrong in RAS’, says Bregnballe, ‘though rare in itself, is invasive disease, either from the water source – particu- larly if it’s a lake or a river – or from the fi sh themselves, which could bring in parasites. This was certainly an issue in Danish trout farming. These issues can be overcome if you use water from an underground source and using disinfected eggs.’
Smolt farms tend to use RAS rather then fl ow-through sys- tems because they can control all aspects of the process. However, Bregnballe has seen many farmers come unstuck because they haven’t stuck to the principles of clean wa- ter and disinfected eggs. ‘Further- more, when people design their own systems, they don’t allow for sub-optimal conditions’, he says, ‘times when they are either over- or under-producing. An overloaded system, for example, can cause stress amongst the fi sh, which can cause lasting damage.’ It is for this reason that Bregnballe wrote A Guide to Recirculation Aquaculture, which was published in 2010. Bregnballe is quick to point out that he is not suggesting that recirculation is the best technique for fi sh farming. ‘Indeed, you could never compete with Norwegian cage-based salmon production’, he says. ‘However, it is ideal for smolt and super-smolt production. My father – who is alive and well at eighty-four – once told me that “if you want to grow big fi sh you should do it when they are small.” This is very true in fi sh farming: smolts grow around fi ve per cent of their body weight every day,
whereas for larger salmon this fi gure is only 0.5 per cent. Thus, if you give the smaller fi sh the ideal conditions using RAS, the return will be enormous.’
When it comes to deciding what constitutes a small fi sh, ie when it is not feasible to grow fi sh in a recirculation system, it very much depends on the species and the market value. ‘If it has an expensive selling price, keep it in RAS, but if it is sold for less then it is better off being transferred to sea cages as quickly as possible,’ says Bregnballe. However, this is not to say that larger fi sh cannot be commer- cially viable in RAS. ‘It’s all about economies of scale: for trout, a farm using recirculation should be looking for a harvest weight of at least 500 tonnes; for salmon 1,000 tonnes’, he explains. ‘AKVA Group designed and built a 2,000 recircu- lation system for Danish Salmon in the north of Denmark, and they are just beginning to harvest their fi rst crop.’
So whilst the jury is still out on the issue of whether farming salm- on in closed RAS is commercially viable, there is less doubt about whether the system itself works – just as long as it has the correct design, it is managed properly and the staff always follow best practice. FF
www.fishfarmer-magazine.com
Principles of RAS Arvo-Tec Feeding Network
Collects data from all fish farming processes
Local area network with PC-computers and MS Windows user interface.
Feeding control units, measurements and alarms.
Feeding process control PC server. All information in a database.
Cable, radio or LAN communication.
Alarms via GSM.
Robot Feeding System or single Feeder units.
The Arvo-Tec Feeding Network has been designed to manage the complete data flow relating to feeding, measurements and alarms from one or more farms. Robot Feeding and Individual Feedin systems can be combined into the same network. All necessary parameters can be easily changed and there is a facility for remote control of your farm from a different office or using remote control technology. For big companies several farms can be handled from the same system.
See our website
www.arvotec.fi 67
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