The benefits (and dangers) of seafood.

As inhabitants of the global village it is no longer a novelty for many of us to travel to far-flung locations on business or holiday. When in Rome do as the Romans do and true to the old saying the adventurous amongst us tend to 'go native' during our periodic travels and try local delicacies.

For those of us who enjoy seafood one of the pleasures of travel is to sample the different varieties of fish.

Seafood is an excellent source of protein and it contains many vitamins and minerals. It is also believed to be low in saturated fats and rich in polyunsaturated fats and Omega-3 fatty acids.

However, as oceans become increasingly polluted, there is an increased risk of seafood becoming contaminated with toxins that may affect our health.

Several toxic substances could affect seafood such as certain chemicals and metals together with micro-organisms. Some toxins are found naturally in some marine algae and can build up in seafood which shares the same environment. 

Toxins can be produced by naturally occurring marine algae and can accumulate in fish and shellfish that inhabit the same marine environment.

Some of the more common sources of toxins in fish and shellfish are listed below:

Mercury

This metal is commonly found in rivers and lakes in the proximity of areas where coal is burned. It then enters the ocean where it converts into Methyl mercury. Small amounts of this substance are found in most seafood varieties and. although there is no scientific evidence regarding the effects on health of this substance, there are concerns about its impact on the developing fetus.

Dioxins

Dioxins are a group of stable chlorinated chemicals, involuntary by-products of some chemical processes and of combustion processes from domestic and industrial waste and sewage sludge. These chemicals can remain in the environment for long periods of time and they accumulate in animal and human body fat.

There is evidence that long-term exposure to these substances is associated with cancer and that it might affect the immune, nervous and reproductive systems.

There is no consistent international standard on recommended dioxin levels. The European Union limit for dioxins in food is 4picogram of dioxins per gram of seafood (one pictogram per gram is equivalent to one part per trillion). There is no longer a limit set in the USA, as they decided to opt for dietary advice.

Ciguatera Food Poisoning (CFP)

Ciguatoxin is a marine toxin sometimes found on certain tropical saltwater reef fish such as snapper, mackerel and grouper, which accumulate toxins when they feed. An early sign that fish is contaminated is tingling or numbness around the mouth. The sexual organs, viscera and scaleless warm-water or reef species are more likely to be affected.

Paralytic Shellfish Poisoning (PSP)

Found mainly in bivalve mollusks such as clams, oysters and mussels, when toxins produced by microscopic algae build up in the shellfish.

Scombrotoxic Poisoning

Caused when bacteria decomposes the red flesh of some fish such as tuna, mackerel and skipjack and certain tinned fish such as anchovies and sardines producing histamine poisons.

Pufferfish Toxin

Toxins found in pufferfish, mainly Tetrodotoxin, can cause serious problems in humans if not prepared properly. Symptoms include swallowing and talking difficulty and a sensation of numbness and paralysis around the mouth.

Microbes

Although less common, there are a number of illnesses produced by microbes carried by seafood.  The main ones are the Vibrio cholerae and Norovirus bacteria found in shellfish

How to minimise the risk of food poisoning

Unlike bacteria and parasites, toxins are not destroyed by cooking and food poisoning from toxins can have serious, and in very rare circumstances lethal, consequences.

1. If collecting shellfish, check local health officials advice and recommendations;
2. Gut and freeze fish as soon as caught;
3. Buy seafood from reputable sources and handle it properly;
4. Exercise caution when eating fish and shellfish that has been caught in unfamiliar waters;
5. Avoid eating very colourful reef fish or fish that has a bizarre appearance;
6. Steer clear of eating pufferfish in a restaurant unless you are certain that staff know how to prepare it safely for human consumption;
7. Skin any reef fish or tropical fish before eating and avoid consuming the sexual organs of these fish;
8. Avoid eating seafood sold as bait, as these products are not subject to the same stringent health and safety regulations as those meant for human consumption;
9. Avoid eating barracuda, in particular that from the Caribbean;
10. To reduce the level of dioxin in your diet, keep to a balanced diet with a wide variety of fresh fruit and vegetables and low fat dairy foods as the toxin is fat-soluble and accumulates in fatty tissues of seafood;
11. Seek urgent medical assistance if you experience any adverse symptoms after eating seafood.

Conclusion

Despite the potential concerns associated with eating seafood, it is a proven fact that seafood, in particular oily fish, is an excellent source of nutrients. Some research shows that people in the UK only eat about a third of the recommended in take if oily fish and that, seven out of ten of us do not eat any at all.

Although it is true that some fish may contain toxins, provided that basic food safety principles are strictly adhered to there is no reason for alarm regarding the consumption of some toxins in very small, and often insignificant quantities.