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Fish farming: just add water and a drop of science

Aquaculture & Society…

Fish farming: just add water and a drop of science

Fish farming: just add water and a drop of science

Aquaculture & Society


In the early 1970s, the Highlands & Islands Development Board (HIDB) speculated that salmon aquaculture would be a profitable but crofting-style activity producing a few thousand tonnes of fish a year. Today, the industry produces around 160,000 tonnes a year and has the ambition to produce 210,000 tonnes by the year 2020. The shellfish industry has also seen significant expansion over the same period and, although volumes are relatively low, there is an aspiration to double the size of this sector to 13,000 tonnes by 2020. And scientists in Scotland are playing a key role not only to improve production, but also to combat the threat of disease and monitor environmental impacts.

Aquaculture has become a mainstay of parts of Scotland’s coastal economy, as the largest producer of farmed Atlantic salmon in the EU and third-largest globally alongside Norway and Chile. The Scottish industry is worth approximately £600 million at farm gate prices, accounting for over one-third by value of Scotland's food exports, with recent year-on-year increases of 5.6 per cent. In fact, farmed salmon ranks only second to whisky in terms of export value. The industry also has wider social importance, especially in remote areas of the west coast and islands, where it provides an important source of local employment.

Today, the aquaculture industry in Scotland employs about 6,000 people and helps to underpin sustainable economic growth in many rural and coastal communities, particularly in the Highlands and Islands. Whilst the salmon industry is dominated by relatively few large multinational companies, other parts of the sector, such as trout and shellfish, are usually small privately-owned businesses.  

More than 50 per cent of the world’s seafood is now produced through aquaculture. Capture fishery production has plateaued at about 100 million tonnes and, even if fished sustainably, is unlikely to increase. Demand for seafood is increasing as a function of population growth and increases in per capita consumption – aquaculture will have to grow to meet this demand. But the issue is not just the basic provision of affordable protein – the world's growing middle class wants seafood that is safe and appetising and salmon is particularly valued.

Given the importance of the industry and the huge growth in global demand, the Scottish Government has agreed to support industry targets for aquaculture:

1    To increase fin fish production to 210,000 tonnes (from 164,380 tonnes in 2012)
2    To increase shellfish production to 13,000 tonnes (from 6,525 tonnes in 2012)

Aquaculture is a vibrant and increasingly important industry in terms of food security as well as the economy, and the Scottish Government has a “very positive” view of its future and is keen to engage with both the industry and the researchers who are driving the science and trying to ensure its sustainable growth. With increasing funding to support aquaculture research emerging through the recently-approved Scottish Aquaculture Innovation Centre, the potential for specific aquaculture initiatives filtering through from the UK Research Councils and the prospect of significant investment in sectorally-relevant research through the EU’s Horizon 2020 programme, the MASTS Sustainable Aquaculture Forum has been involved in developing a comprehensive research strategy designed to help focus and influence the allocation of these funds to agreed priority areas for research and innovation. The majority of Scotland’s aquaculture-related research capacity comes together through MASTS. The Institute of Aquaculture at the University of Stirling is a recognised international centre of excellence for aquaculture. Other world-leading expertise in fish disease and immunology is based at the University of Aberdeen. Throughout the University of the Highlands and Islands network and at the Scottish Association for Marine Science (SAMS), there is a wide range of expertise in assessing and helping to mitigate the environmental impacts of aquaculture. St  Andrews University has a focus on fish molecular genetics and interaction between aquaculture, seals and cetaceans. Edinburgh Napier and Heriot-Watt Universities also have specific interests in aquaculture. Marine Scotland Science (MSS) has tight links with all academic research institutions within MASTS through studentships and research fellowships, and carries out high-quality research across the full spectrum of subjects in relation to Scottish aquaculture, including epidemiology, pathogen and disease characterisation, host–pathogen interaction and immunology, and interactions between aquaculture and environment. MSS supports the Scottish Government by provision of highly-applied evidence-based research, consequently used to support relevant policies.

The domestication and intensification of any farming system will inevitably result in unintended impacts. The pace of aquaculture expansion over the last 30 years has been meteoric in comparison to established terrestrial agriculture, much of which has evolved over many hundreds of years. Disease is a particular challenge and the majority of the UK’s research expenditure on aquaculture is focused in this area. For aquaculture, the UK maintains a very high health status within the EU, which maximises our potential to export our aquaculture products. But occasionally, as with every other form of animal and plant production, significant disease challenges emerge. Monitoring the health status of farmed fish and shellfish is a statutory responsibility of the Fish Health Inspectorate, which is based at the MSS Laboratory in Aberdeen. A close working relationship with MSS scientists and the wider aquaculture health and welfare-related science community helps to ensure that, for most diseases, we have the capacity to identify emergence, track their spread and suggest a range of treatments. However, the range of available fish medicines is limited and needs to be expanded, and fish vaccines in particular need to be developed for a range of pathogens. Imagine the difficulties of treating many thousands of fish, often in very difficult conditions, at sea. That is why we need treatments that
are both efficacious and easy to administer.

In the past, outbreaks of the virus Infectious Salmon Anaemia (ISA) have had a devastating impact on the salmon industry – if detected, the stock must be destroyed. Maintaining high levels of biosecurity on farms is critical to preventing such infections occurring and spreading. ISA was responsible for reducing Chilean salmon production by a third a few years ago and it is only just recovering to previous production levels. Sea lice are a particular problem for some salmon farms. A naturally-occurring ectoparasite of Atlantic Salmon, sea lice can proliferate in farming situations, where they have large numbers of captive hosts. The industry is committed to minimising the numbers of lice infecting their farmed fish and a range of treatments and management measures have been developed, to maximise the welfare of the farmed fish and minimise any potential impact on wild migratory salmonids. However, the capacity of all pathogens to develop resistance to treatments means that farmers need a range of efficacious medicines which they can use to minimise the potential for disease resistance to develop. For sea lice, the hunt is on for new in-feed treatments, the development of biological controls using wrasse, which act as cleaner fish by picking off and eating the sea lice on farmed salmon, and – the holy grail – a vaccine. Selective breeding for resistance to a number of diseases is also progressing on a number of fronts.

State-of-the-art molecular biology is also  being used to understand and investigate  ways to cure  diseases, combining this with integrated pest management to optimise the use of treatments and minimise the potential for disease to become established.

For many years, Scotland has been recognised internationally as a centre of expertise and training for aquaculture. The Institute of Aquaculture (in Stirling) and the University of Aberdeen in particular have generated a large number of graduates, MSc and PhD, who now work around the globe. Many have risen to senior positions in their respective countries and are keen to maintain links with the UK. Work conducted at SAMS, the University of St Andrews and MSS has fed directly into regulation of the aquaculture sector. Indeed, one of the underlying rationales for maintaining high levels of scientific expertise in this field is to ensure that the UK has a strong and authoritative voice in EU and wider international debates framing policy and legislation relevant to aquaculture. The UK leads many EU-funded research projects and plays an active role in driving and co-ordinating the aquaculture research agenda. Strong links with Norway, Ireland and Canada have resulted in collaborative research on fish disease. Scottish scientists also have an active presence in South America, notably Chile. Southeast Asia, with over 270 different species being produced through aquaculture, has been a fertile area for research and international students. Many of the economies in this region have moved from “developing” to “emerging” over the last 20 years – this status is now being recognised and the UK’s recently-announced £375-million Newton Fund is specifically targeted at forging strong collaborative research links with these countries – many of which have important aquaculture sectors.

No silver bullet

One of the discussed topics concerning salmon aquaculture revolves around the naturally-occurring, endemic, native parasite – the sea (or salmon) louse. As its name suggests, it  is found in sea water and feeds on the skin and mucous of salmon, which has been mooted as a possible selection pressure leading to leaping behaviour. The earliest known recordings of sea lice causing discomfort of salmon date from the writings of an 18th-Century Scandinavian bishop, whilst mortality events in Scotland were first depicted  by Lewis in 1905. A year later, sea lice research was conducted in Aberdeen by an early predecessor to Marine Scotland.

Management of sea lice is a high priority for Scottish fish farmers, because if it is left unmanaged, farmed salmon health and welfare could be reduced. As such, an estimated £30 – £40 million per year is spent by the sector in applying management methods such as: using veterinary medicines; coordinating production (such as stocking, fallowing and the use of single-age class cohorts); stocking cleaner fish as biological controls; recording lice counts for informing treatments; using functional feeds; and rotating medicine use to avoid resistance. 


Sustainability and the future

Fish are one of the most efficient animals at converting their food into protein that humans will eat - outperforming chickens, sheep and cattle.

This is an important strategic issue in terms of food security, because some of the raw materials used in animal feeds may become limiting as the demand for food increases. For those forms of aquaculture that rely on raw materials such as fish meal and fish oil, sourcing alternatives has become the focus of significant research effort.

Fish oil is the main source of Omega 3 in our diets. Omega-3s are considered essential fatty acids, meaning that they cannot be synthesised by the human body. Although many of the health claims associated with consumption of Omega-3s remain controversial, they are implicated in helping to reduce the risk of some cancers, inflammation, cardiovascular disease and developmental disorders. As a result of extensive research, the salmon and trout sectors are now able to optimise the use of marine-sourced Omega-3s, thus reducing their reliance on global supplies; but ultimately it is recognised that as aquaculture expands, alternative – probably plant-based – sources of this feed ingredient will need to be found. Similarly, fish meal has been an important component of some fish diets and, whilst some plant-based replacements have been found and are in use, the search continues for alternatives that have the appropriate amino acid profiles, digestibility and palatability.

Unlike terrestrial forms of farmed animal production, many of the species we now cultivate in aquaculture are little changed from their wild counterparts. Selective breeding programmes are becoming ever more sophisticated and our ability to target desirable production traits is also advancing rapidly. A combination of better disease treatments and alternative feeds, coupled to selectively-bred stock with improved disease resistance and the capacity to use feed materials more efficiently and from a wider variety of sources, will help to ensure that aquaculture continues to be sustainable.

In Southeast Asia, polyculture, or integrated multi-trophic aquaculture, has been practised for thousands of years. A typical example might be to feed household waste to chickens, for the chickens droppings to be used to fertilise freshwater ponds to stimulate the growth of phytopkankton as the basis of a food chain designed to feed fish, which will eventually be harvested as a source of food and income. However, “Western” aquaculture – a more recent development – has evolved as a series of monocultures, with production focused on single species. A considerable body of research over the last 15 years has explored the potential to integrate shellfish and seaweed production with finfish production to create a “virtuous” and potentially profitable circle, with the shellfish and seaweeds assimilating the particulate and soluble waste from the fish farms to produce additional marketable products, whilst reducing the environmental impact of the fish farm. Whilst in principle this scenario has merit, so far it has not provided sufficient economic or environmental benefits to attract widespread acceptance by the industry. However, as the industry continues to expand, and pressure to use our marine “space” more efficiently increases, co-location of aquaculture developments, and hence multi-trophic scenarios, may well start to appear.

There is no doubt that aquaculture will continue to expand globally – there is little alternative if we are to feed the rapidly- growing population and one whose per capita consumption of food derived from both marine and freshwater sources is increasing. The UK, and Scotland in particular, is well placed to contribute to that development. Although we cultivate relatively few species, we should not perhaps be concerned. Other forms of terrestrial agriculture have flourished by developing different varieties of a few domesticated species. We do not farm different species of chicken, pigs or cattle – we have simply selected desirable traits and created the huge variety of farmed animals we now accept. The speed with which aquaculture has expanded has resulted in some environmental issues, which will need to be continuously monitored and addressed. Disease, as with other forms of intensive terrestrial agriculture, remains a significant and ongoing challenge. A robust regulatory regime, together with existing research capacity and a positive policy landscape, suggests that aquaculture in Scotland will expand and be sustained in the longer term. Our capacity to support and influence the development of aquaculture globally through collaborative projects and providing world-class education and training will also ensure that we will continue to contribute to food security and support fragile rural economies.

Which species?


Salmon are the most successful and most popular fish farmed in Scotland, enjoying an almost iconic national status on a par with Scotch whisky, but other fish are also farmed and various experiments have been conducted in the past to see if other species would be both practical and profitable.  One venture to farm cod was not a success – because the economics didn’t work. Whilst cod stocks were depleted and feared to be close to collapse, other white fish such as haddock were still being caught in large volumes, and although farmed cod was targeted as a high-value niche product, production costs were still too high to attract a sufficiently large enough customer base to support an industry.

There has been considerable investment in developing halibut and, whilst it is produced in small volumes, the difficulty and associated cost of producing consistent numbers of high quality juveniles continues to limit the potential of this sector to expand. The UK led the development of turbot as an aquaculture species, but more favourable climatic conditions for on-growing in France and Spain ultimately led to production moving out of the UK. Trout remains a mainstay in terms of land-based production, but volumes remain low and the large retail market is focused on salmon – although some sea trout and rainbow trout are produced in small volumes at sea.  Other finfish species have been explored, ranging from sole, seabass, lumpsuckers, hake and haddock to more exotic species such as tilapia and barramundi produced in land-based recirculating water systems. All, for various reasons, have failed to take off commercially in the UK.  


European lobsters have long been an interest for aquaculturists and fishermen. For many years, the UK Government invested heavily in this species, with a view to restoring and enhancing wild stocks. However, the economics of this process remain challenging and, whilst production of lobsters for restocking is carried out, the real commercial value of this process is highly questionable. With respect to aquaculture, interest remains, but production costs and risks remain high and this will continue to limit ambitions with this species. However, a recently-awarded multi-million Euro grant to assess the potential for culturing the European Crawfish in a land-based recirculated water facility in North Wales may hail a new frontier.

Scallops are cultivated to a limited extent and there is recognition that demand for this species could outstrip wild-caught supply. However, the time for stock to reach a marketable size continues to limit investment in large-scale cultivation. The blue mussel grown on ropes is now a familiar sight in many Scottish sea lochs and there is potential to expand production of this sector, given appropriate growing areas and export markets.

Pacific oysters remain popular and there is renewed interest in cultivating native oysters. Some companies have dabbled with other shellfish species, such as tropical prawns in recirculating systems, but again, the economics remain challenging.

Bivalve shellfish are highly efficient filter feeders and, as a result, they have the capacity to concentrate both food and a range of potential natural and human-derived contaminants.

Maintaining high water quality is fundamental to the long-term sustainability of this industry. Some types of phytoplankton (algae) are toxic, forming harmful algal blooms. Whilst these are a natural occurrence, they are regularly responsible for contaminating shellfish, preventing harvesting and sales until toxin levels are deemed safe by the Food Standards Agency (FSA). Bacterial and viral contamination of shellfish as a result of sewage overflow is also a periodic problem which impacts on public health and is, therefore, carefully monitored by the industry and the FSA. Thankfully, Scottish coastal waters are generally of a high standard which, coupled to ongoing monitoring by industry and regulators, ensures that products from Scottish shellfish farms conform to rigorous hygiene standards and contribute to an expanding area of aquaculture production.

There is no room for complacency, however. Parts of the mussel shellfish sector have been forced out of business in recent years because of the increased presence of Mytilus trossulus – a mussel species that although not recognised as non-native, in some conditions outcompetes Mytilus edulis – the blue mussel we are familiar with. This species of mussel is associated with a lower meat yield and has a particularly fragile shell, which makes the individuals less economically desirable, ultimately reducing the profitability of the sector. Further research is needed to understand the conditions which favour this economically-damaging species and what impact this species and its hybrids with M. edulis have on the sustainable growth of the Scottish shellfish industry. 


In China, seaweed farms are so large that they can be seen from space. Most of this production is for human consumption. In the West, seaweed is very much a niche market and one generally served through the harvest of wild stocks. However, with increasing interest in the use of seaweed as a source of biomass for energy production and the potential to extract some useful and potentially valuable by-products, pilot-scale plots of seaweed production have been established.


The authors

Dr Nabeil Salama

Salama is an epidemiological modeller concerned with the transmission of pathogens or parasites, such as sea lice, in the aquatic environment, both from wild fish to farmed individuals, and between and within aquaculture facilities. He has been based at the Marine Laboratory in Aberdeen for five years and spent the early part of his career studying terrestrial diseases. He uses epidemiological and oceanographic models to investigate the spread of disease, in order to inform spatial methods of disease management.

Dr Matt Gubbins

Gubbins is the manager of the Marine Spatial Planning Programme at Marine Scotland Science, based at the Marine Laboratory in Aberdeen. An ecotoxicologist by training, Matt has acted as an advisor to the planning and regulatory processes for marine aquaculture in Scotland since 2001. His work in marine spatial planning involves using models to map the constraints on future fish farm locations and identifying optimal locations, so the industry can expand in a sustainable manner.

Dr Iveta Matejusova

Matejusova is a group leader of the Aquaculture and Environment Group at MSS, based in Aberdeen. She joined MSS in 2001 as a parasitic taxonomist and ecologist, later moving on to molecular genetics, focusing on the molecular characterisation of fish pathogens, host–pathogen interactions and molecular epidemiology. In her work, she uses her background and novel molecular technology to study the genetic basis of susceptibility and resistance of fish and shellfish hosts to a range of aquatic pathogens and the transmission of pathogens in aquatic environments, and  develops diagnostic tools for the discrimination of pathogen strains and populations.

Dr Mark James

James is the Operations Director of MASTS, but for the last 20 years has worked at the interface between science, industry and policy in aquaculture. This has involved running a number of large collaborative programmes of aquaculture-related research.  








"Fish farming: just add water and a drop of science ". Science Scotland (Issue Fifteen)
Printed from on 07/04/20 06:30:15 PM

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