Fish Farming and Aquaculture

Fish Farming

Fishing factory Ardglass Northern Ireland

Fishing boats unloading their catch at a fish processing factory in Ardglass, Northern Ireland.

Every year millions of cows, pigs, sheep and other farmyard animals are slaughtered by the million, and yet these species are still abundant due to intensive breeding programmes. If this is successful with livestock why can’t the same thing be done with fish? The answer is that it is already being done on a vast scale, but the results can be destructive. Aquaculture – also known as aquafarming – refers to the farming of not just fish but also molluscs, crustaceans, and aquatic plants in an artificial environment. On a worldwide level it has been claimed that around 40% of the aquatic life which is consumed by humans comes from aquaculture (1). The scale of aquaculture and fish farming can be seen in these statistics:

  • Around 45 million tons of fish, shellfish and plant life is raised in aquaculture for human consumption every year (2).
  • The aquaculture market was worth an estimated £55 billion in 2009 (2).
  • The aquaculture industry has grown by around 9% a year since the 1970s (1).
  • Human demand for aquaculture products has doubled in the last thirty years (1).
  • In the USA around 90% of shrimp eaten by humans is farmed, either domestically or farmed abroad and then imported (2).
  • Freshwater fish is the most farmed species accounting for almost 24 million tons per year. Molluscs and aquatic plant provide around 13 million tons. Marine fishes only account for about 1.5 million tons (2).
  • China is by far the biggest producer of aquaculture, raising over 30 million tons in 2004. India is next with around 2.5 million tons. Vietnam, Indonesia and Thailand all produce around a million tons and every other culture involved in aquaculture produces less than one million tons per year (2).

 The Problems with Fish Farming

The appeal of aquaculture is plain to see. Many natural fish stocks are under immense pressure and many are already being fished at an intensity which is unsustainable. In several parts of the world fish stocks have collapsed completely, bringing unemployment and lasting long-term damage to both economies and communities. With world demand for fish and shellfish products rising the ability to farm fish and shellfish and take the pressure off natural fish stocks has great appeal. However, as we will see farming fish is fraught with problems and in many cases raising stocks of fish in this way can do much more harm than good.

For a start large scale fish farms can see fish living in very poor conditions. Fish being intensively farmed can live their whole life in less space than the average bathtub (3), and as the agriculture industry has seen with battery farmed and caged hens consumers are taking a much greater interest in the welfare of animals and it is likely that many consumers, in affluent countries at least, will be put off by intensively farmed fish. Furthermore the way in which fish are closely packed together can lead diseases spreading through populations quickly – in 2016 salmon prices rose as an epidemic of sea lice hit fish farms on the west coast of Scotland. Antibiotics then have to be used to treat the fish which leads to these chemicals being inside the fish which will eventually be eaten by humans – understandably, this does not go down well with consumers. Additionally chemicals are also used to promote growth in the fish and control populations and some fish may need chemical treatment just to survive in captivity. Many fish farms in the developing world have less regulation over the chemicals which can be used, and many chemicals which are banned or heavily restricted in the USA and Europe are widely used in less developed countries (3). There is much debate about the long term effects of consuming fish which have been treated by these chemicals and concern about the effects that these chemicals have on the wider marine environment and food chain.

Global Total Fish Harvest

Global total fish harvest from 1950 – 2010. As catches of wild fish have levelled off the worldwide demand for fish has been satisfied through massive expansion of the fish farming and aquaculture industry.

Many fish farms – especially those in the developing world – are basically isolated sections of natural lakes and rivers, in which the fish are raised in nets and cages. These are extremely susceptible to being ripped open by storms or predators which would see the farmed fish released into the natural environment, potentially spreading disease into the wild and harming local genepools (3). This has already been seen in the Pacific Ocean where an estimated 225,000 farmed Atlantic salmon have escaped in recent years. The effects of farmed and wild fish interbreeding on the gene pool are unknown (4). Problems may be even worse if genetically engineered fish escape and mix with natural populations. A report by Canadian researchers published in May 2013 highlighted the dangers, stating that if genetically modified salmon escaped they were capable of breeding with brown trout and creating hybrid young fish which carried modified genes. These young fish would be extremely fast growing meaning they could out-compete native fish, potentially decimating natural populations of both trout and salmon. In their defence fish farming companies such as Aquabounty (more on them later) stated that all of the genetically modified salmon they produced were sterile and held on tanks on land meaning that the chances of escape into the wild were negligible. Even high-tech fishing farms can have major issues. In early 2013 the Sunday Times reported that Pescanova – a Spanish commercial fishing company which is the world’s biggest – lost £25 million worth of turbot when the filters of the pond system they kept the fish in became blocked with sand. Without the filter system all of the fish suffocated, wiping out their entire stock.

In January 2017 the UK media reported that the wholesale price of salmon had increased by fifty per cent in the previous year due to infestations of sea lice in Scottish and Norwegian fish farms. The lice infest salmon and feed on the gills and flesh of the fish, with fish farm owners claiming that climate change is making the parasites more common. The lice infestations have led to lower numbers of salmon being produced by the farms, with one Scottish fish farm admitting they had inadvertently killed around 175,000 salmon by trying to rid them of sea lice. The reduction in European sea lice was exacerbated by reduced numbers of salmon being produced by Chile, a major producer of farmed salmon. Chilean salmon farms have been badly hit by a deadly algal bloom which has caused major supply shortages to worldwide markets.

The reduction in the amount of farmed salmon reaching the market means that price rises are inevitable, along with further bad publicity for the fish farming industry.

Shrimp Farming

A shrimp hatchery in South Korea

A shrimp hatchery in South Korea.

Shrimp farming is beset with its own series of problems. Beginning as a benign, small scale activity carried out by individual farmers in the 1970s shrimp farming has expanded dramatically to satisfy the massive demand for all kinds of prawn and shrimp species that comes from North America, Europe and Japan. Today around 2.6 million tons of farmed shrimp are produced every year, worth around £5.7 billion (2). The vast majority of shrimp farms are in Asia and concentrate on producing just two species – Pacific white shrimp and tiger prawns. Shrimp farming is destructive because large areas of land are cleared to create the ponds that are needed to raise shrimp in. Previously this could be done in small natural ponds, but with demand for shrimp and prawns growing constantly bigger and bigger ponds have been used. Today the ponds used in modern shrimp farming can be up to one hundred hectares in size. However, these ponds need to be in saline water meaning that mangroves (forests and trees which grow in saline water on the edge of beaches) need to be cleared to create the ponds for prawns. The removal of mangroves can trigger coastal erosion, damage seagrass beds and deprive animals of both a food source and a habitat (5). It is thought that around 38% of the world’s mangroves have been destroyed to make way for shrimp farms (6). The problems of chemicals and diseases that are apparent in fish farming are also encountered in shrimp farms.

The Fishmeal Trap

Inside the Grandi fish processing plant in Reykjavík, Iceland

Inside the Grandi fish processing plant in Reykjavík, Iceland.

Even when fish farms are well-run, well-organised, disease free and prevent fish from escaping there is still a major problem – the fishmeal trap (6). This is a simple problem: the fish in fish farms need to be fed, and they are usually fed with small fish species processed into fishmeal. However, the mass removal of small fish species from the sea to create fishmeal will leave wild fish and other marine creatures with nothing to feed on, causing massive problems in the world’s oceans. Fishmeal is  made by processing small forage fish such as sandeel, European sprat, sardines, Pacific saury and anchovy. Larger species with a low commercial value such as pouting may also be used, as may the remains of big fish carcasses such as shark after the valuable parts such as the flesh and liver have been removed. The process involves a highly mechanised system which dries, grinds, cooks and crushes the fish to produce fishmeal in the form of a powder of a cake. This is then sold on to the fish farms.

The problem arises because huge amounts of fishmeal need to be produced every year to supply the fish farms. It is thought that around 5-6 million tons of low-value forage fish are turned into fishmeal every year (7), it is not hard to see why – to raise 1kg of average fish in a farm 1.9kg of fishmeal is needed. With highly carnivorous species such as salmon the ratio goes up to 5kg of fishmeal per kilogram of fish raised (4) . For ranched tuna (tuna are not farmed as it is very difficult to hatch their eggs in captivity, instead they are ‘ranched’ i.e. caught in the wild as juveniles and then raised in underwater cages) the ratio is worse again. Bluefin tuna can eat 10% of their bodyweight every day (8), meaning that an incredible 22kg of wild pelagic fish needs to be used to supply a single kilogram of tuna meat to a sushi restaurant (8). While the mass removal of small species and forage fish may not have a direct effect on humans (as people do not eat these species) the knock on effects will be felt by pretty much every single species that lives in or around the sea. An estimated 90% of fish in European waters feed on sandeels at some point. Mass removal of sandeel to supply the aquaculture business would be disastrous. No-one can accurately predict what the effects would be but the following scenarios are all likely:

  • Mackerel will fail to migrate to Britain, as the follow sandeel shoals, or they could migrate here and starve to death as there will be nothing for them to eat (9).
  • Predatory fish such as pollock will fall in number, and those that remain will be forced to move offshore to hunt in deeper water to hunt for different species (9).
  • Sandeel-dependent marine birds such as puffins, guillemots and gannets will fail to breed due to starvation and lack of food. There have already been reports of poor breeding seasons and chicks dead through starvation as the parent birds have been unable to supply them with sandeels (10).
  • Dolphins and porpoise often feed exclusively on sandeel and may well starve if this species become less abundant (10).
  • Large amounts of fry and immature fish species such as cod and haddock are taken when fishing for sandeel and other forage species. Danish fishing vessels have been reported to catch immature salmon along with sandeels. Both species are then turned into fish meal which is used to feed farmed salmon, meaning salmon in farms are effectively eating the young of their own species – a more destructive scenario is difficult to imagine (11).

The depletion of small and forage species from the seas due to the commercial fishmeal industry is a major issue and one that needs to be addressed. In many ways it is a bigger problem than overfishing specific species because if the small prey fish are gone then the vast majority of marine life will suffer. The knock on effects of eliminating a whole section of the food chain are unknown, and the only accurate prediction that can be made is that the results will be hugely damaging to almost all forms of marine life.

Sand eels and puffin

Sandeels are essential to the marine eco-system as they provide food for a huge range of species from fish and seals to marine birds such as puffins.

Some also raise a moral point about the fishmeal industry. By scooping low-value forage fish indiscriminately from the sea and turning them into fishmeal we are depriving (poor) people of this cheap source of food (while western nations will not eat sandeel people in poorer countries will). Is it really a good use of the world’s marine resources for developed nations to catch 5kg of edible forage fish only to effectively turn it into 1kg of salmon?

There has been some progress in changing the feed which is given to farmed salmon. In 2016 the news emerged that the amount of healthy omega-3 found in farmed salmon had halved between 2006 and 2015. This was because the amount of small forage fish contained in salmon feed has fallen significantly, with plant based materials being used instead. This has led to a corresponding fall in the amount of omega-3 found in salmon. Part of the reason for this is due to the rocketing demand for salmon meaning that supplies of fishmeal made with wild caught fish simply cannot keep up. The 2016 National Food Survey carried out by the Department of Environment, Food and Rural Affairs found that the amount of salmon purchased by UK consumers had increased by 550% since the mid 1970s.

‘Super Salmon’

Some biotechnology companies are based around genetically engineering fish in order to make aquaculture more productive. One of the most famous is Aquabounty Technologies, a company which describes itself as “a biotechnology company dedicated to the improvement of productivity in aquaculture”. This company has developed hybrid trout, salmon and tilapia which grow twice as fast as normal fish. The salmon they produce, for example, have extra genetic material and are ready for market in eighteen months, rather than the usual three years (12). The company is floated on the AIM (Alternative Investments Market) but appears to be in bad financial condition with the Sunday Times stating that its “cash reserved had shrunk and in February [2012] it tapped shareholders for $2m (£1.3)” (12), and was forced to reduce its staff from twenty-seven to twelve (13).

Safe Fish Farming

Despite the problems with fish farming there are certain species which are perfectly safe to farm. Mussels and other forms of shellfish are a great species to farm. For a start they are filter feeders – animals which feed by straining water through filters in their body to remove food particles suspended in the water. In this way mussels actually clean and purify the water they are in, rather than polluting it. Furthermore, mussels do not produce the waste product problem in the same way as fish, are less susceptible to diseases and obviously can’t escape from farms in the same way that fish can. Mussels raised and farmed are therefore massively preferable to wild mussels which have been caught by dredging – a process of dragging weighted metal cages over the seabed which wreaks havoc on the natural environment and marine ecosystems.

Tilapia is a generic name for a variety of freshwater fish. These fish are ideal for farming as they are fast growing, disease resistant and prolific breeders that can adapt to living in a range of environments. Crucially, they can live, and indeed thrive on a diet consisting mostly of plants and vegetation, meaning they avoid the issues associated with the fishmeal trap. Sales of tilapia are on the up in the USA, having quadrupled throughout the 2000s (14), and this can only be a good thing for the stocks of other species of fish.

With traditional fishmeal factories one answer is to utilise waste products from other species. For example the heads and guts from filleted cod, haddock and plaice could be used to make fishmeal, rather than sandeels and sprats. This is done to a varying extent around Europe. Spain and Germany has fish processing plants that run exclusively on fish trimmings and waste products, but Denmark – by far Europe’s biggest producer of fishmeal – uses 90% forage fish. A move towards the fishmeal industry purely using waste products would be a good thing indeed.

Where Now for Fish Farming?


A tilapia in an aquarium.

Despite the drawbacks and dangers of fish farming there has to be a future for safe aquaculture. A series of artificial farms safely and responsibly producing hundreds or even thousands of tons of prime cod, plaice, bass and sole each year to satisfy commercial demand would allow commercial harvesting of wild fish to be scaled back dramatically, allow the stocks of fish in the sea to return to something close to natural levels. However, with no answer to the fishmeal trap this appears to be a distant dream. Fish farming in its current form is simply too wasteful and too damaging, and attempts to use fish trimmings and waste products to make fishmeal do not go far enough. Furthermore, fish farms are becoming increasingly technologically advanced. Hydro-acoustic systems are being developed which remotely monitor how much food fish are eating based on the amount of noise they make in the water, allowing fish farms to save significant sums of money by not wasting fish feed. Other developments include automated monitoring of fish to see if they are infected with parasites, laser removal of sea lice and a 110 metre wide floating fish farm which can contain 1.5 million fish (15). It remains to be seen how much these technological advances – and the increase in profits that comes with them – will enhance the expansion of fish farming across the world.

However, all hope is not lost for those promoting sustainable fish farming which does not negatively impact the marine environment. There is real potential with raising herbivorous fish such as tilapia – a species that sidesteps the fishmeal trap issue. However, tastes for the fish we eat in the UK will have to shift dramatically from the big five species (cod, haddock, tuna, prawns and salmon) which dominate UK plates before any progress can be made on this front.


  1. Fish Farming’s Growing Dangers – Time Magazine: Science and Space.
  2. The State of the World’s Fisheries and Aquaculture – Food and Agriculture Organisation of the United Nations.
  3. Surprising Fish Farming Facts – The Huffington Post.
  4. Global Fish Crisis: Are Fish Farms the Answer – The Guardian.
  5. Shrimp Farming – Greenpeace.
  6. Per Gunnar Nordahl, ‘Is the Aquaculture Industry Caught in a Fishmeal Trap‘ – Norwegian School of Economics and Business Administration.
  7. Marine Fish Farming: Solution or Delusion? – World Fishing and Aquaculture.
  8. ‘Ranching’ Tuna the Eco-Friendly Way –
  9. The Fish Meal and Fish Oil Industry and its Role in the Common Fisheries Policy – European Parliament Working Paper.
  10. Sandeels, A Key Supply Chain Food, Are Disappearing in the North Sea – Wildlife Extra.
  11. Sandeels – Scotsac.
  12. Oliver Shah: America Swallows Super Salmon, The Sunday Times, Business Section, page 2, 18/11/12.
  13. An Entrepreneur Bankrolls on Genetically Engineered Salmon – The New York Times.
  14. Two Sides to Every Tilapia – The Washington Post.
  15. How Lasers and Robo-feeders are Transforming Fish Farming –
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