Fish: farmed versus wild

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  • Published: Jun 15, 2016
  • Author: Ryan De Vooght-Johnson
  • Channels: Gas Chromatography
thumbnail image: Fish: farmed versus wild

Overfishing the ocean

Fishing is an ancient practice, a livelihood for millions and a source of food for billions. However, over time we have become greedy, catching more fish than can be replaced. This is called overfishing and has pushed over 85% of the world’s fish stocks to or beyond their biological limits.

Fishing is an ancient practice, a livelihood for millions and a source of food for billions. However, over time we have become greedy, catching more fish than can be replaced. This is called overfishing and has pushed over 85% of the world’s fish stocks to or beyond their biological limits. Some commercially important fish, such as tuna, are even under threat of extinction.

As a result, fewer and fewer fish are being caught from the sea. “In consideration of the sea’s impoverishment due to massive fishing, it is estimated that the consumption of aqua-farmed products will increase in the next years,” explains Dr Rosaria Costa, Professor of Analytical Chemistry at the University of Messina in Italy. Already almost half of all the fish we eat are farmed and by 2030 the majority of fish eaten by humans (62%) will be farmed.

Although the word aquaculture wasn't first used until the mid 19th century, the farming of fish dates back to 6000 BC. Today, aquaculture is one of the fastest growing food producing sectors. By 2022, global aquaculture will increase by 35%, while traditional fishing will only increase by 5%.

This is undoubtedly a good thing for the oceans – but what about consumers? Farming can alter the nutritional composition of fish, changing, for example, the fats it contains. This is of great interest to the scientific community because some of these fats have health-promoting properties. Omega-3, for example, a polyunsaturated fatty acid that humans can’t make themselves, is essential for healthy metabolism and has anti-inflammatory effects.

A new study has investigated this in fish from the Mediterranean, traditionally a popular area for fishing (leading to over 95% of its fish stocks being overfished). A team of researchers led by Dr Costa looked at how the diets fed to fish affect the fatty acids they contain. Dr Costa and her colleagues analysed some of the most common products in Italian fish markets: sea bass and gilthead sea bream (farmed and wild caught), farmed mussels, and clams caught from a local salt lake.

Molecular measurements

The researchers used comprehensive 2D gas chromatography (GC x GC) to fingerprint the fatty acids in the samples, producing bi-dimensional plots to visualise the differences between the fish. The profiles revealed significant differences. “Our GC x GC lipidomic analyses evidenced a higher content of fatty acids in farmed fish, although omega-3 fatty acids were more concentrated in wild individuals,” Costa summarises.

The farmed fish had more fatty acids overall, although the beneficial omega-3 fatty acids were more concentrated in the wild fish. By contrast, farmed fish had more omega-6 acids owing to their specialised diets. This may be of concern as research suggests that excess levels of some omega-6 fatty acids relative to omega-3 may increase the likelihood of some diseases. However, the farmed fish also contained more oleic acid, which can reduce blood pressure. The mussels and clams contained roughly the same fatty acids, although there were some smaller differences in quality.

As well as assessing lipids, the researchers also looked at the mercury content of the samples using a Direct Mercury Analyzer. The accumulation of heavy metals like mercury in wild fish is a particular concern, especially in predators at the top of the food chain, like tuna.

When it came to mercury content, farmed fish were safer than wild caught fish. “Wild-caught fish reported alarming levels, therefore defining cultivated fish as safer,” added Dr Costa. Indeed, levels were 10 times higher than in the farmed fish and reached the maximum limit set by the European Commission. The mussels and clams both had extremely low mercury levels.

Fraudulent fish

Comprehensive 2D gas chromatography coupled with mass spectrometry was thus used to obtain ‘fatty acid fingerprints' in fish and shellfish samples, revealing valuable and novel information.

In the future, the method could be used to detect fraudulently advertised fish. For example, sea bass is now rarely found naturally in the Mediterranean, although many fish sellers claim theirs is wild caught, as it appeals more to the customer than farmed varieties. As well as telling wild fish apart from farmed equivalents, the tool could help guide farmers on how to develop optimal diets for their fish, enhancing the good fatty acids and lessening the bad.

Related Links

Eur. J. Lipid Sci. Technol., 2016. Costa et al., Multidimensional gas chromatographic techniques applied to the analysis of lipids from wild-caught and farmed marine species.

Overfishing

Wiki: Aquaculture

On the state of fish stocks

FAO: Aquaculture

Article by Ryan De Vooght-Johnson

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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