byRob J Davies, Principal Aquaculture Consultant & Head of RAS Projects at Aqua Biotech Group, Malta


In order to survive you must adapt and evolve. As the need for land-based fish farms and research centres grows, so does the need to advance the design and efficiency of such facilities and reduce operating costs to enhance long-term feasibility. In order to do this, new technological advances must be tested before they are implemented in a recirculating aquaculture system (RAS), which makes having an R&D Centre essential.

Moreover, the newer facilities need to see tangible benefits from these recent advances; the more you build, the more efficient and lower the operating costs should be. Replicating the same design over and over is a recipe for failure.

A selection of these new technologies, in combination with those already established, have enabled rapid progress in RAS design in the last few years. The use of micro-dosing of oxygen and ozone using in-system redox and DO probes has allowed for a considerable reduction in the operating costs of these expensive gasses.

The implementation of nano-bubble technology (not to be confused with micro-bubble), where super-saturated oxygen remains in the water for longer without degassing, means that not only the injection efficiency of this gas has improved and is elevated beyond maximum saturation, but its secondary effects of partial sterilisation of water (reducing bacteria and pathogens) and lowering its density (thus helping to reduce pumping costs), has added more benefits to the overall operating efficiency. Lastly, the use of ozonated protein skimming in both sea and freshwater, cannot be underestimated. The benefits of this technology are on multiple fronts:

  • Removing micro-particulates- (Much beyond the capability of low micron mesh drum filters), enhancing water clarity, gas transfer efficiency, sight of feed and appetite, whilst reducing gill irritation and risk of hydrogen sulphide poisoning from excess solids in the system
  • Constant partial sterilisation of the system - Reducing detrimental bacterial colonies and pathogens, and various life stages of some parasites
  • Fish stress reduction - Especially when in handling situations, which improves appetite upon recommencement of normal operations and enhances general health
  • Reduced heterotrophic competition in the biofilter -Increasing its efficiency, whilst partially directly reducing ammonia and nitrite with the use of low levels of ozone
  • Increased degassing of CO2- Especially with the use of cascade type skimmers which combined the skimming process with degassing, and increased oxygen levels in the system as the ozone reverts to oxygen

Despite these operational benefits, realised through the use of ozonated protein skimming, there are still RAS facilities that are being built without this technology. In my experience, this is mainly due to the lack of having in-house R&D capabilities (where working with and testing these technologies encourages advancement of the whole RAS design), as well as the increased capital expenditure of the project with their inclusion.

However, once they are implemented in a facility, the savings and benefits on an operational side far out-weigh the initial expense. There are many new RAS facilities that cannot achieve a good water quality and clarity because of this and hence do not reach their production targets.


Scottish salmon hatchery

One case study of a facility that has included such advanced technologies and is extremely operationally-efficient, is the new salmon hatchery and research facility recently built for the University of Stirling in Scotland. The 240,000 fish hatchery will produce totally clean, reliable and robust stock of salmon that are not challenged by external parasites and do not suffer from low-level disease problems, which will validate the accuracy and reliability of their research.

Alastair McPhee, the Aquaculture Facility Manager, said that the systems '…improve the longer-term value of our research results and potentially prevent trials having to be repeated to test key conclusions…Our design is commercially relevant, with the inclusion of special features being driven entirely by our research requirements'.

He adds that 'Our system, for example, will allow us to recover any feed which isn't consumed and collect any waste created, which are both essential factors when carrying out dietary trials.'

The intake treatment system has been designed to filter a relatively high number of suspended solids and tannins in the water, transitioning it from a brown, muddy appearance to almost perfect clarity. This is being achieved by use of ozone micro-dosing through a cascade freshwater protein skimmer, automatically controlled with a redox probe measuring the ozone level at the highest point of saturation. The system is also fitted with degassing, UV sterilisation and a secondary redox probe as further treatment and safety features.

The use of the ozone, protein skimming and UV with incoming water of such low quality, demonstrates the extent of the cleaning ability that this treatment process can have, even in freshwater.

The egg incubation room is supplied with top-up water filtered to one micron and the ambient air temperature is controlled to closely match the water temperature. The custom-built incubation trays are individually fed so that each of the eggs obtain a uniform amount of oxygen and new water, providing the best environment to produce healthy, robust fry.

The 24 tanks in the on-growing system are equipped with full environmental and monitoring system control, including such features as photoperiod and temperature manipulation, as well as oxygen and ozone micro-dosing, low-level ozonated protein skimming, carbon dioxide monitoring and degassing, and full individual feeding control and pellet/faeces collection.

The water is clear, with efficient macro and micro-particulate solids removal and constant partial sterilisation. The high degree of filtration is clear in the abundance of brown foam produced by the ozonated protein skimming and sludge from the drum filter effluent.

The design features of this facility and the minimal operating costs evident by the low power consumption of the singular pumping point in the system, show what is possible to achieve in a truly modern and advanced RAS with a progressive design. If this efficient use of oxygen, ozone and power was to be utilised in large scale fish farm designs for new facilities, their operating costs would be kept to a minimum and RAS feasibility for post smolt salmon and other species would increase.


The future of RAS

Many failures in RAS facilities over the past 20-30 years have their roots not only in their fundamental design constraints, operational costs and lack of management with the correct RAS experience, but also in their financial plan and the production target. I have recently visited several large-scale RAS farms across Europe and have yet to see one with water quality and clarity good enough to provide optimal growth conditions to produce healthy fish.

Many of the new seawater facilities for post-smolts still do not utilise oxygen, ozone, protein skimming and pumping power in the most efficient way, but instead use an old design with sub-standard grade materials and equipment that consume a large amount of power, with the result being high operating costs, but low design and construction costs.

outcome being that the facility is unable to produce the expected tonnage or numbers as the sub-optimal water quality suppresses the growth of the fish. This, together with the high operating and maintenance costs, means that the farms are likely to fail to meet their projected financials.

In the near future, this approach must change to ensure sustainable farming operations. The constant development and testing of new technologies and inclusion into modern large-scale RAS is paramount in order to reduce operating expenditure and provide the fish with truly optimal conditions, to achieve maximum growth potential and fulfil the financial projections of the farm.

As a former large-scale seawater RAS manager, I have experienced these complications first hand, but in the last 10 years I have seen that the technology to produce a truly well-designed RAS farm with low operating costs and good water quality currently exists (as evident in the new salmon hatchery and research facility for the University of Stirling).

It just needs to be implemented by potential RAS farm owners, choosing to invest in a facility that includes the latest technology and that will provide the lowest operating costs - as opposed to the lowest capital investment with unachievable production targets and unobtainable financial projections.

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