FISH FARMING AND FARMED FISH - AN INTRODUCTION BY PAUL COURTNAGE, PROJECT OCEAN VISION

Increasing demands on wild fish stocks by commercial fishing has caused widespread over-fishing and depletion of wild stocks. Some estimates predict that, at the current rate, 90% of our fisheries will be completely fished out by 2050. Fish farming is seen as a solution to the increasing market demand for fish and fish protein. So, as wild oceanic fish stocks decline, fisheries and other related businesses have turned to fish farming or aquaculture. They have promoted their efforts as ecologically sound on the grounds that they do not take wild fish from the environment, but rather from captive-bred stocks. However, the story of fish farming is more complex than that and the debate around fish farms and about the health risks to consumers between public health experts and scientists has tended to obscure the significant environmental problems associated with farming fish in the sea or in rivers and lakes.

Fish Farms South of Gozo, Malta. Photo by Courtney, Project Ocean Vision 2011

Most of the problems associated with fish farms stem from the intensive farming of carnivorous fish species such as salmon, which are fed a diet of ground fish and fish oil. I use salmon as an example of farmed fish here because of the prevalence of salmon farming and the fact that the farming of this species has been well researched. But please don't think that means other species are not extensively farmed. A look at the fish counters in many supermarkets has revealed farmed barramundi, tuna, bream, carp, catfish, cod, crayfish, halibut, mud-crab, mussels, scallops, sea bass, tilapia, tropical prawns, trout and turbot.

In intensive aquaculture systems (fish farms), fish density can be increased far above those that occur in nature (in the region of 5-6 fish per square metre), as long as sufficient oxygen, clean water and food can be provided; the use of pens in open ocean is seen as a means of providing these necessities and will be familiar to most readers. There are several problems associated with raising carnivorous fish in these high-density fish farm pens, one of the biggest being pollution, which results from uneaten food and faecal matter. This is dangerous to the farmed fish and places considerable stress on the environment in the vicinity of the fish farms.

Fish farmed in these cramped conditions are constantly in contact with each other and the sides of the pens; this can cause damage to their fins, leaving them vulnerable to disease. The constant contact also promotes the spread of parasites between fish in the farms. Common fish farm infections include Gyrodactylus salaris (a parasite of the skin, gills and fins of salmon and trout) and Infectious Salmon Anaemia (affects salmon in seawater and there have been several outbreaks in Scottish fish farms). Actually, these infections are not confined to the fish farms, but are freely transferred to local, wild fish populations. In response to this, fish farmers started to use large quantities of pesticides, antibiotics, and other chemicals to control algae in the water, promote fish growth and combat disease in the farmed fish populations. These chemicals are harmful to the local ecology in the vicinity of the fish farm and the residual presence of these drugs in human food products has become highly controversial. The use of antibiotics in food production is thought to increase the prevalence of antibiotic resistance in human diseases.

Marine fish farms were originally established simply as netted pens in relatively open water. As a result of faulty netting and rough seas, large numbers of captive fish have escaped from the fish farms into the environment. These escaped farmed fish present an immediate and severe threat to wild fish populations by competing for food and habitat and spreading fish parasites with which they were infected in the fish farm. Moreover, some escaped fish have been found to breed with local populations, changing their genetic constitution, especially where genetically modified fish are farmed. Researchers tend to agree that wild salmon stocks have not been boosted by escapes from fish farms, but rather are replaced by them. As an illustration of the extent of this problem, a single incident in 2005 saw half a million salmon escape from a Norwegian fish farm, whilst a similar incident in Chile led to the escape of one million fish. As much as 90% of the salmon in some rivers of the Faroe Islands, Norway, Scotland, Ireland and Canada have escaped from fish farms. These fish are inevitably beginning to spread out and invade new areas.

Probably the biggest problem with fish farming is one of resources. Top-level carnivores in fish farms require feed that is usually derived from wild-caught fish. To an extent, vegetable proteins have replaced some fish meal for carnivorous fish, but vegetable oils have not been successfully incorporated into their diets. Although the food conversion efficiency of fish is considerably higher than in cattle, it still takes between two and three kilos of wild fish to produce one kilo of farmed fish. Fish farms can use more protein in feed than they produce in farmed fish. So, despite claims that fish farming reduces pressure on wild fish populations, the opposite may in fact be true. The farming of marine fish can actually increase pressure on wild fish such as sardines, anchovies and herring that are commonly used in fish meal for use in fish farms. This also places additional stress on other parts of the marine food web that depend on these wild fish for food.

Fish farming has also been linked to habitat destruction around the globe. For example, mangroves that protect low-lying coastal areas are being destroyed to make way for tiger prawn farms in Thailand, Indonesia, Malaysia, Bangladesh and South America. The removal of mangroves for the constructin fish farms has been directly implicated in the large number of people killed by tropical storms in the coastal areas they used to protect.

Producers and politicians have claimed that farming fish in the ocean is similar to raising livestock on land. However, cattle, sheep, and poultry are herbivores that eat little or no animal protein – unless they are given animal protein in their feed, the catalyst that caused the BSE outbreak in the 1980s. In truth, raising carnivorous fish in fish farms is more analogous to capturing large numbers of wild deer to feed to farm-raised wolves for food. And, of course, until they get very much better at breeding these fish in captivity, marine aquaculture still relies on taking considerable stock from the wild; freshwater fish farms are better at harvesting eggs and raising fish from their own stock.

All too often it is not facts, but economic and political expediency that win arguments and the issue of fish farming is no exception. For example, Scotland is the biggest producer of farmed salmon in the European Union - the only countries in the world that produce more are Norway and Chile. Scottish fish farms produced around 151,000 tonnes of farmed fish in 2009 and a total of nearly £434,000,000 worth of fish and shellfish per year - The Scottish Fish Farm Production Survey 2009 is available here. So Scottish fish farming is big business. The fish farming industry has already created 1,500 jobs in rural areas with few other economic opportunities and this number is expected to triple as the industry grows. So this is not a business proposition that any politician is likely to oppose, regardless of a few environmental concerns. Fish farming is not going to go away. And I must ask the question, "why should it?". Better perhaps to make it sustainable and ecologically responsible so that it really can become the solution to our over-fished oceans. This will take legislation (which is starting to appear), enforcement and the engagement of the producers (the fish farm owners).

Environmentally friendly fish farming methods provide the alternative to high-density, open ocean cage aquaculture, substantially reducing or eliminating the risk of environmental damage through the use of re-circulating aquaculture systems (RAS). This involves a series of culture tanks and filters through which water is continuously recycled - much like a good garden pond on a very large scale. The fish farm water is treated mechanically to remove solid particles and biologically to convert harmful chemicals, mainly nitrates, into less toxic or non-toxic ones. UV sterilization, ozonation, and oxygen injection are also used to maintain water quality. Efficient systems can be 'closed' and require little or no water exchange between the fish farm and the local environment. RASs can minimize many of the environmental shortcomings of aquaculture: escaped fish, water usage, and the introduction of pollutants and infection into the environment.

Lower fish densities in fish farms also mitigate the impact on the environment, but the use of RASs and lower density farming involve much higher capital and operating costs and are, therefore, seen as less attractive commercial options as long as consumers continue to buy intensively farmed fish.

Regarding legislation, it is encouraging that in January 2009, Mainstream Scotland, part of Norwegian salmon company Cermaq, paid £13,000 in compensation to the Forth District Salmon Fishery Board after the escape of juvenile salmon from a freshwater fish farm on the River Devon. Regulations and inspection schedules are slowly forcing fish farm operators to control escapes, water quality and disease, but there is still a long way to go. Scottish fish farmers are working hard with the Scottish government to improve their ecological credentials within the framework of the Aquaculture and Fisheries (Scotland) Act 2007.

There is also some good news regarding breeding. In Australia, Hagen Stehr appears to be close to breeding bluefin tuna in captivity, avoiding the need to deplete wild stocks. Work continues.

As with many environmental issues two of the most effective methods for reducing the environmental impact of fish farming, aside from regulation, are campaigning and education. There are a number of organizations that are campaigning for the use of environmentally friendly processes in fish farms. By promoting better understanding of the issues, we can persuade consumers to choose their sources of farmed fish carefully. This actually applies to a wide range of fish (wild and farmed) available in our shops, restaurants and supermarkets and we would encourage you to read our Guide to Buying Fish.

If you need more incentive to think carefully about fish farming, consider the issue of food safety. Polychlorinated Biphenyls (PCB) are toxic chemicals, classed as persistent organic pollutants, that accumulate in soil and rivers and that eventually end up in the oceans. PCBs are mixtures of synthetic and organic chemicals that were developed for their high combustion temperatures making them useful fire retardants and insulators. They have a carcinogenic effect and are released into the environment through leaks, illegal dumping and waste oil from electrical equipment. 

The greatest risk for human exposure is through eating fish that have fed in waters polluted with PCBs and have absorbed the toxin. The fish at greater risk are carnivores because they feed on contaminated fish and accumulate higher PCB levels in a process called bio-accumulation. One of the most serious risks of PCB exposure is through the consumption of farmed salmon. As we have seen, these are fed fish feed designed to be high in fish oil and it is in the fish oil that PCBs are most concentrated. Consequently, many farmed salmon ingest dangerous levels of PCBs that may make them unsafe to eat more than once in a month (advice from the US Environmental Protection Agency).

Farmed salmon tend to lack the rich pink colouration of wild-caught fish and, so, some producers have used a pink dye to make their product appear more natural to consumers. This colourant has been linked with retinal problems in humans.

Summary

This is a short article, intended as an introduction to fish farming and to raise some of the ecological and food safety issues. It is not exhaustive, but highlights the risks to local fish populations through disease, water pollution, the release of chemicals and drugs into the wild and the escape of captive stock from fish farms. It also points to the pressures on habitats and wild stocks presented by the need to catch prey species to feed the farmed fish and the need to replenish stocks from the wild in some cases.

However, fish farming is by no means all bad news. Governments have been alerted to the problems by research and conservation organizations and more responsible administrations are doing much to work with their producers and to introduce workable legislation in order to mitigate the impacts of fish farming. There is a long way to go; for example, the development of treatments for disease and parasites does appear to alleviate stress in the captive stock, but does not necessarily reduce the risk of infection to local wild fish. Whichever way they pen these fish, remember that they are taking free-swimming creatures that are programmed to roam vast oceans and confining them to small cages with thousands of other fish; it will never be a perfect solution, think of it as the piscine equivalent of battery hen farming.

We should hope and expect that the introduction of lower density farming, the replacement of netted pens with more secure cages, the use of RAS and the development of fish breeding programmes are all milestones on the route to more ecologically sustainable fish farming. For now, consumers will need to choose between fish produced in less responsible fish farms and fish produced in farms that are working hard to raise their game.

So how do we recognise ecologically sound farmed fish? The Marine Stewardship Council eco mark is usually a good guide to buying fish, but this organization is focussed on wild fisheries and, so, does not certify fish farms. Under EU law, nothing captured or harvested from the wild may be labelled organic, so this label can only be applied to farmed fish. At the moment, the organic label is your best guide to buying farmed fish. But further research is a good idea if you can identify the provenance of the fish. Many advocates of organically produced food are yet to be convinced by the conditions in organic fish farms and I tend to empathise with their doubts. Shellfish farming is, in my experience, far more eco-friendly and sustainable than fish farming.

To be eco-friendly, fish farms need to use a RAS, should employ organic farming methods to avoid exposure to chemicals and antibiotics and not keep fish in high densities. Consumers should try to buy locally produced fish where possible to avoid adding a huge carbon footprint to all the other issues with fish farming. I do, however, wonder how consumers will compare the quality of the food from fish farms compared with the beauty of wild-caught salmon.

Fish farms have their supporters in scientific and conservation circles; organisations concerned with feeding an exploding global population see fish farms as one of the best solution to global food production. One thing is for sure, if responsible consumers and critical conservationists are to accept fish farming, fish farmers must accept and welcome the science that could improve the ecology, ethics and quality of their business. If they do not, the bad news will simply be compounded by a lesser quality product and unsustainalbe, unsupportable practices. With continued pressure, fish farms may yet become the solution to the decimation of our oceans' wild fish stocks.

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Courtney - Project Ocean Vision