Aquaculture produces safe,
Just as with wild-caught fish, farmed seafood represents an excellent source of nutrients important for human health. There is hard evidence that regular consumption of fish lowers the risk of coronary heart diseases because of high concentrations of omega-3 poly unsaturated fatty acids. Other important nutrients in farmed fish are vitamins A and D for maintaining healthy bones, eyes and skin. Farmed fish is also a rich source for iodine, important for the proper functioning of the thyroid gland, and selenium, which is an important anti-oxidant.
Because farmed fish and shellfish are produced under controlled conditions, it is possible to maintain the highest quality standards from the egg to the plate. In the same way that business processes may be certified to meet standards (e.g. ISO), aquaculture production also has certification schemes. They are increasingly supported by various codes (of conduct and of good practice), developed at national and European levels.
Production of fish and shellfish on farms allows for consistent and even enhanced levels of the elements in seafood that do us good. For example, the level and balance of omega fatty acids, vitamins and minerals such as iodine and selenium can all be influenced through specially designed fish feeds.
What are the health benefits of seafood?
Much of the importance of fish in health has come from research into long-chain polyunsaturated fatty acids (PUFA) of the n-3 family. Other abbreviations used are omega-3 and n-3 fats. Fish is a rich source of two important PUFA: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). PUFA are present in both wild and farmed fish. DHA and EPA are found in abundance in the flesh of oil-rich fish but they are also present in lean fish.
The effect of PUFA on coronary heart disease has been extensively studied. The human body cannot make PUFA. There is strong evidence from many scientific studies that PUFAs from fish play a major role in protection against heart disease . PUFAs may also help prevent other illnesses, such as arthritis, Alzheimer’s disease, some types of cancer and asthma. Extensive research to confirm these relationships is ongoing.
How much seafood should we eat?
Different values exist in the scientific literature for what is the “ideal” daily or weekly intake of EPA and DHA for human health. Government advice varies considerably between countries. However, as a general rule, a healthy diet is generally assumed to include 1-2 fish per week, especially fatty fish.
The International Society for the Study of Fatty Acids and Lipids (ISSFAL) suggests an uptake of 500 mg of EPA + DHA per day or 3.5 g per week provides enhanced cardiac health in adults.
In its 2004 report “Advice on Fish Consumption – Benefits and Risks”, the UK Scientific Advisory Committee on Nutrition (SACN) concluded that the majority of the UK population does not consume enough fish, particularly oily fish, and should be encouraged to increase consumption. The Inter-Committee Subgroup endorsed the Committee on Medical Aspects of Food Policy (COMA) 1994 population guideline recommendation that people should eat at least two portions of fish a week, of which one should be oily. Consumption of this amount would probably confer significant public health benefits to the UK population in terms of reducing cardiovascular disease (CVD) risk and may also have beneficial effects on foetal development.
Current advice from the UK Food Standards Agency suggests a weekly intake of up to four 140g portions of oily fish for men, boys and women over reproductive age, with the caveat that girls and women of reproductive age should only consume two portions of oily fish per week2.
Safe seafood products
Because it is a controlled food production process, fish farming can include safeguards to protect its product from contamination. Ironically, the main source of contaminants in farmed fish (such as trace amounts of dioxins, PCBs and mercury) is fish feed composed of wild fish. However, because this food can be sampled and analysed prior to feeding, maximum limits of contaminants in fishmeal and fish oil used in aquaculture have been established by international law.
Data from the official controls of the fish feed ingredients and analysis of the farmed fish itself are available for consumers, authorities and industry alike.
Strategies to minimise contamination of farmed fish by way of feed derived from the wild are in place and can include; careful selection of the fish oil source, purification of fish oil prior to its inclusion in fish feed, and partial replacement of fish oil by vegetable oils.
A number of factors have combined to make us more aware than ever of the safety of food. Firstly, increasingly accurate measuring techniques allow us to detect even the lowest levels of contaminants. Secondly, increasing media focus on food safety has highlighted issues such as BSE, dioxins and salmonella, and ‘food scares’ have become regular features of news broadcasts. For food to be acceptable, it must be proven to be safe to eat.
Food safety standards have been developed giving clinically proven safe levels of food constituents that may at higher levels provide a risk to health.
Contaminants and health risks
Contaminants in fish derive predominantly from their diet. Whilst it is not possible to control the diet of wild fish, the levels of contaminants and some nutrients in farmed fish may be modified by altering their feed.
Strict EU regulations (e.g. Directive2002/32/EC) and controls by food
safety authorities ensure that contaminants are kept well below dangerous
levels in farmed fish. Emerging technologies allow fish feed producers to
purify fish meal and oil before it is incorporated in the feed.
The retention of dietary mercury by fish is dependent on dietary concentration and the duration of exposure to the contaminant. Methylmercury (the toxic form of mercury in fish) is present in higher amounts in large predatory fish such as swordfish and tuna. High consumers of such top predatory species, such as pike or tuna (especially fresh or frozen bluefin or albacore tuna), may exceed the provisionally tolerable weekly intake (PTWI) of methylmercury.
The greatest susceptibility to the critical contaminants (methylmercury and the dioxin-like compounds) occurs during early human development. For a developing human foetus, this means that the risk comes from the amount of these compounds in the mother’s body.
Furthermore, EU maximum limits exist for a range of contaminants in food such as dioxins, dioxin-like PCBs, mercury, lead, cadmium and polyaromatic hydrocarbons (the maximum level is for one PAH, BaP). These limits include food of farm origin and other foods such as fish from capture fisheries.
Monitoring programmes exist to document the levels of contaminants in wild and farmed fish to fulfil a need for independent data for consumers, food authorities, fisheries authorities, industry and markets.
As in land farming, fish farming benefits from traceability technologies to monitor and follow the production cycle through its entirety. While traceability itself is not a guarantee of safety, it is essential in pinpointing problems, should they occur, throughout the whole production chain. This is not just limited to producers, but encompasses their suppliers, processors and distributors. Such “full chain traceability” is most effective when all links in the chain have the same principles and use the same (or at least compatible) tools.
In 2002, an EU-funded concerted action initiative called “TraceFish” (www.tracefish.org) produced three consensusbased standards for the recording and exchange of traceability information in the seafood chains.
One of these is a standard for farmed fish. The basic element in the system is a unique identification number to be placed on each lot of products in such a way that traceability can be transmitted electronically. The system is voluntary.
Traceability tools are being continuously improved and are major monitoring components of various labelling and certification schemes for aquaculture products.
An example of this is the TRACE initiative (www.trace.eu) that is using 5 case studies in food to improve traceability parameters and measure food authenticity. This last point has specific interest for fish products and TRACE is developing generic low cost analytical tools for use in the traceability infrastructure that verify geographical origin, production origin and species origin.
Affordable seafood products
As fish species become scarcer in the oceans, they will become less affordable to consumers.
All of the approximately thirty species of fish in European aquaculture production have shown a decrease in farm gate price as their production volume has increased, while improvements in production techniques have resulted in ever-increasing quality.
Figure 5: EU production and price trends – for several aquaculture species produced in Europe.
Data from FAO FishStat 2006. Note prices in US Dollars.
Atlantic salmon and rainbow trout are almost exclusively farmed. They are now comparable in price to land farmed produce such as chicken and pork.
The availability of ‘new’ farmed species (sea bass, sea bream, cod, sole, scallops, octopus etc.) has the potential to provide this increase in affordability to all consumers.
Quality of life of aquatic animals
Infectious diseases are encountered in all food production. Fish and shellfish may be more under threat from disease than land animals or plants because germs survive longer and can spread more effectively in water. The rapid identification and treatment of bacterial and viral infection is therefore crucial in aquaculture. While best management practice remains the preferred option for producers, the use of therapeutic agents may sometimes be necessary.
National and international regulations have been implemented to approve veterinary medicines that do not compromise food safety. An example of this is the so-called ‘withdrawal period’, defined as the minimum time to elapse between termination of the treatment and harvest of the animal. Withdrawal periods are specific for each drug and each utilisation of that drug, for example to treat bacterial disease.
It is important to note that the use of veterinary medicines such as antibiotics has greatly decreased in many types of aquaculture. For example, in Norway the use of antibiotics in salmon and trout farming has been negligible for the last 10 years due to the use of better vaccines. In 2004, Norway produced 23 times more salmon and trout than in 1985; in the same period, the use of antibiotics dropped by a factor of 25.
Figure 6: Antibiotics used in Norwegian farming of trout and salmon 1980-2004.
The principal challenges in aquaculture are now related to viruses and parasites. For example, “sea lice” threaten farmed salmon in temperate waters. However, non-medicinal and environmentally friendly lice treatments are being developed. In Norway, for example, wrasse, another fish, is used to eat the lice from infected salmon.
With the adoption of tighter laws and regulations, and with the difficulties of drug companies registering new treatments for aquaculture, the availability of medicines to treat aquaculture species becomes increasingly unsure. More and more, research is therefore turning towards prophylaxis as a solution.
Parasites are common in wild fish, too
Parasites are not unique to farmed fish, but in the wild they obviously go untreated. Parasites fall into two main groups – ectoparasites, which affect the skin and external organs, and endoparasites, which invade the body and attack the musculature and internal organs.
Ectoparasites include several types of sea lice, crablike creatures that eat the skin and flesh of the fish. If left untreated, they will cause considerable suffering to the fish and open wounds on the skin of the fish that may become sites for disease.
Endoparasites include nematode worms that enter the body of the fish through the mouth, infest the gut and can then burrow into the flesh of the fish. As well as reducing the fish’s ability to regulate the amount of salt in its body by perforating the gut membrane, they also reduce the saleability of the flesh, since fish infested with nematode parasites are not saleable for human consumption.
As on land-based farms, when animals are held at higher densities parasites can infect a stock relatively rapidly. Because unhealthy fish mean substantial loss to the farmer, however, it is uncommon in modern fish farms to find harmful burdens of parasites. Outbreaks are controlled by modern farming practices and the use of medicines that authorities have deemed safe to the fish, to consumers and to the environment.
(1) Simopoulos, A.P. “Essential Fatty Acids in Health and Chronic Disease”. Am J Clin Nutr 2000; 71 (suppl): 5065-95.
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