Quality of life for the planet

Need for high quality water and other resources

Clean water is the primary pre-requisite to successful aquaculture. A clean environment is therefore critical for its commercial success. Any environmental impact that would compromise the quality of the water used on fish farms must be monitored and minimised through appropriate siting (choice of locations) of farms and production processes.


In recent years, the development of aquaculture has raised some associated environmental concerns. Like any farming operation on land, fish farm cages produce waste materials. These fall into three categories – uneaten feed, fish faeces and dead fish. Most of the environmental impacts of aquaculture can be managed and minimised through understanding of the processes involved, responsible management and the effective siting of farms.


Uneaten feed – Should uneaten feed reach the bottom of a cage, processes that break it down can reduce the amount of oxygen in the sediment. In severe cases, oxygen levels in the water above may also decrease, creating “anoxic” conditions in which only a few animal species can survive. Should the feed contain antibiotics used to treat the farmed fish above, bacteria in the sediment and the natural breakdown of waste material might be affected.

In practice, fish farmers do everything they can to prevent such a situation, since the cost of fish feed amounts up to 40 percent of the total production cost. Feed reaching the sediment is lost, and it is in the farmer’s interest to minimise such waste. On well-managed farms, feeding is carefully regulated to ensure that the maximum amount of food is taken up directly by the fish and farmers aim to ensure that less than 5 percent of the feed is wasted. To improve uptake by fish, feed pellets are manufactured to either float or to sink slowly through the water.

Fish faeces – Unlike land animals, fish do not generally produce compact solid faecal material and more often excrete a loose cloud of faecal material that is easily dispersed by water currents. In still conditions, however, faecal material can build up beneath fish cages. It is, however, not in the farmer’s interest to let this happen, since the buildup of faecal material can lead to anoxic conditions which affect the fish above. Fish farmers wanting to ensure the health of their fish will frequently check the bottom below their fish cages to ensure that faecal material is not building up. In addition, in many EU Member States, the government employs diving teams to carry out inspections.
If faecal build-up is observed, farmers will be advised to move their cages, allowing the bottom to recuperate for a short period, however full recovery typically takes between three to ten years. In recent years, improved feed formulations have also been introduced that fish digest more efficiently, producing less waste.

Fish farmers generally avoid overly sheltered and stagnant sites, preferring areas that contain a healthy flow of water through the cages. Such flows disperse fish faeces so it can enter the natural food chain.

Dead fish – Dead fish are a loss to the farmer and a potential health hazard to the stock as well as a source of pollution. Fish farmers will, at all times, endeavour to minimise the number of dead fish on their farms and to remove such mortalities where they occur.

Fish farms are required to report significant fish deaths when they occur and are inspected by state agencies at least twice a year.

Shellfish cultivation

Shellfish such as oysters, mussels and clams are filter feeders and take their food directly from the water in which they live. This means that they do not require supplementary food and, if anything, actually improve the quality and clarity of the water. Shellfish farming can only provide the best quality products if practiced in pristine environments with the highest water quality.

Environmental problems can arise on shellfish farms where the animals are held at overly high densities, leading to depletion of food in the water and build-up of faeces below the holding areas. Both effects will harm the outcome for the farmer and hence shellfish farms are generally sited where water exchange is high and the stock is kept at densities that are compatible with the level of water exchange. In many cases, stocking densities on farms are lower than those of clusters of shellfish (e.g. mussels) that occur on natural beds.

Shellfish farms have been thought to disturb wildlife habitats by taking up space on a beach where wading birds feed. It has been shown, however, that wading birds and oyster farms can exist side by side. The fallen oyster or mussel can have a positive impact on a bird’s feeding pattern.

Other potential impacts include the importation of parasites, pests and diseases onto the shellfish farm which would then spread to other areas. The microscopic oyster parasite Bonamia ostrea, for example, gradually spread through Europe with the spread of oyster farming. Oyster farmers have responded by significantly reducing the density at which their shellfish are farmed.

Some people complain of “visual pollution” caused by large numbers of floating barrels or shellfish trestles in otherwise unspoilt areas. Low-profile and dark-coloured floats have recently been developed to minimise the visual impact.

Pond fish farming

Fish pond systems represent the oldest fish farming activity in Europe, at least dating back to medieval times. Ponds were built in areas where water supply was available and the soil was not suitable for agriculture. The wetlands of Central and Eastern Europe are good examples of this. The total European production from pond farming is approximately 475,000 tonnes. About half of this production is cyprinid fish, such as common carp, silver carp and bighead carp. The main producer countries are the Russian Federation, Poland, Czech Republic, Germany, Ukraine and Hungary.


Typical fish ponds are earthen enclosures in which the fish live in a natural-like environment, feeding on the natural food growing in the pond itself from sunlight and nutrients available in the pond water.

In order to reach higher yields, farmers today introduce nutrients into the pond such as organic manure. This is accompanied by stocking of fingerlings and by water being flushed through the pond. Fish pond production, however, remains ‘extensive’ or ‘semi-intensive’ (with supplementary feeding) in most countries, where semi-static freshwater systems play an important role in aquaculture. Chemicals and therapeutics are not usually used in such ponds. Hence the main environmental issue is the use of organic fertilisers, which may cause eutrophication in the surrounding natural waters. The use of organic fertilisers is regulated at national levels.

Extensive fish ponds are usually surrounded by reed belts and natural vegetation, thus providing important habitats for flora and fauna. They play a growing role in rural tourism. Many pond fish farms have been turned into multifunctional fish farms, where various other services are provided for recreation, maintenance of biodiversity and improvement of water management.

In areas where water is scarce, some farm systems recirculate, treat and re-use their water. Such systems are generally self-contained and therefore pose little threat to the environment. Solid waste material produced in such systems is rich in organic compounds and often used as a fertilizer elsewhere. Alternatively, new hydroponic systems have been developed to grow vegetables and other food crops in the nutrient-enriched water. There is much interest in these systems, but their economic viability remains challenging.

Trout farming in flow-through systems


The most widely-practiced form of inland aquaculture in Europe is trout farming. Water is taken from the river, circulated through the farm and treated before being released downstream. All water in the farm is renewed at least once per day. Where more than one farm exists on the same river, it is in everyone’s interests that the quality of the outflowing water from one farm is good, as this then becomes the inflowing water for the next farm. Other water sources include spring water or drilled and pumped ground water. In some countries, heated industrial water sources (such as electricity generating plants) are used to increase the water temperature (by heat exchange)
used in the farm, thereby saving energy costs to heat the water. Geothermal water also provides naturally warmed water, thus allowing the farming of new fresh water species (especially eel, sturgeon, perch and tilapia) with low environmental impact.



trout farm

Recirculation Aquaculture Systems

Recirculation Aquaculture Systems (RAS) are land-based systems in which water is re-used after mechanical and biological treatment so as to reduce the needs for water and energy and the emission of nutrients to the environment. These systems present several advantages such as: water and energy saving, a rigorous control of water quality, low environmental impacts, high biosecurity levels and an easier control of waste production as compared to other production systems. The main disadvantages are high capital costs, high operational costs, requirements for very careful management (and thus highly skilled labour forces) and difficulties in treating disease. RAS is still a
small fraction of Europe’s aquaculture production and has its main relevance in The Netherlands and Denmark. The main species produced in RAS are catfish and eel but other species are already being produced using this type of technology such as turbot, sea bass, pikeperch, tilapia and sole.


Other environmental impacts of fish farming – the case of escaped fish

It is inevitable that fish farmed in net pens in either fresh or salt water will sometimes escape into the wild. In some cases, there will be a small but steady release of fish. Sometimes, large numbers will escape due to severe damage to the net pen by way of storms, predator attacks or vandalism.


There has been vigorous debate on the potential impact of escaped farmed fish, in particular salmon, on wild populations. On the one hand, it has been suggested that escaped farmed salmon could compete for living space, breeding partners and food resources, spread disease, or interbreed with wild fish, causing “genetic pollution” and thereby weakening the wild strain and reducing its ability to survive . On the other hand, scientists have argued that farmed salmon, which are bred for fast growth in perfect conditions, are less able to compete for food, territory and mate in the wild than their wild colleagues. Therefore, a limited escape of farmed fish would be unlikely to have a serious effect on wild fish populations. Only if very large numbers of fish escape into a small area, would interbreeding occur and the fitness of the local population potentially be reduced.


In its Aquaculture Europe 2005 conference, the European Aquaculture Society invited the North Atlantic Salmon Conservation Organisation (NASCO) to hold a special workshop on the interactions between wild and farmed salmon. The summary report of this event “Wild and Farmed Salmon – Working Together” drew the following main conclusions:

Through the use of single bay management, single generation sites and synchronised fallowing, real progress is being made in relation to minimising impacts of diseases and parasites, which are key issues for wild fish interests. The development of third-party audited containment management systems may represent a significant step forward. The liaison group should look more at the possibilities of rearing all-female triploid salmon, which could eliminate genetic interaction with the wild stocks, but which need to be balanced by the production cost of these fish, as well as consumer resistance to what could be seen as genetic manipulation.

Restoration programmes can benefit from fish farmers’ expertise, but habitat protection and restoration have equal or greater importance in species restoration than stocking programmes alone.



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