MESA logo
  Seaweek 2010    
Home | About MESA | Contact MESA | Seaweek | Site Resources | Marine Links | International News | MESA History

SW10 Home |  Links | Teaching Ideas | Gallery | Action projects   |   Background Information

Seaweek 2010: Oceans of Life - ours to explore; ours to restore

So what's wrong with fish?
by David Ogilvie

Fish and human health

Many people who eat fish and seafood believe that doing so is healthy. According to an August 1997 survey of 10,000 households in the US, commissioned by the National Fisheries Institute, more than half the respondents cited health benefits among their top reasons for eating fish and seafood. More than three-quarters believed consuming fish to be healthier than eating beef, pork or poultry. And most believed the quality of the seafood they had eaten was good. But the widely held public perception of seafood as health food is simply one whopper of a fish story!

The facts:

Omega-3 Essential Fatty Acids

There is no question that Omega-3 fatty acids are important in the human diet, and no-one disputes that they are found in fish oils, mainly those from cold water fatty fish. Many people are not aware, however, that flaxseed (linseed) oil contains nearly twice as much Omega-3, contains no cholesterol, is lower in saturated fat, and does not contain the often high levels of toxic chemicals, such as mercury, that can bio-accumulate in fish. A study published in the November 2002 issue of the New England Journal of Medicine showed mercury levels to be directly associated with the risk of myocardial infarction (heart attack) and that high mercury content may diminish the cardioprotective effects of Omega 3 fatty acids found in fish. (9) So in actual fact, flaxseed is a preferable source of Omega 3, particularly for people trying to reduce their cholesterol intake. (For more information refer to our nutritional article on Omega-3 fatty acids.)

A lot of fat and cholesterol, and no fibre

Fish and seafood generally contain excessive amounts of fat and cholesterol, with no fibre. Many people say they eat fish rather than beef in hopes of limiting fat and cholesterol. However, many fish, such as shark, catfish, swordfish, and sea trout, contain almost one-third fat, while salmon and orange roughy contain over 50%. Regarding cholesterol, prawns have double that of beef, and a three ounce serving of salmon, for example, contains 74 milligrams of cholesterol, about the same as in a comparable serving of T-bone steak or chicken.

Fish also contains significant amounts of protein, which may be okay if your diet is low in protein, but the average person on a Western diet already consumes roughly twice as much protein as is recommended. Excess dietary protein is not a risk-free indulgence; it has been linked to obesity, kidney disease and osteoporosis.

Bio-accumulation of toxic chemicals

Think about where fish and shellfish live. Everything from human waste to industrial waste ends up in our rivers, lakes, and oceans. Consequently, fish and shellfish can accumulate extremely high levels of toxins and chemical residues in their flesh due to "bio-accumulation". Big fish eat little fish and the bigger the fish (e.g. tuna and salmon), the longer the food chain, and the greater the bio-accumulation. Concentrations of toxins can be as high as nine million times those found in the waters in which fish and shellfish live. Shellfish also contain high levels of toxins because of their filter-feeding habits.

Fish may be loaded with mercury, lead, and industrial pollutants like PCBs (Poly-Chlorinated Biphenyls), DDT and dioxins. These chemicals have been linked to kidney damage, cancers, nervous disorders, impaired mental development, foetal damage, and many other health problems. And when nursing mothers eat fish, not only do they expose themselves to these contaminants, they also pass half of the toxins that they consume along to their babies.

These days, it is very difficult to find a piece of fish that hasn't been exposed to some contamination.


Mercury is a naturally occurring element that makes its way into the environment from power generation and through industrial pollution. Rain washes it into waterways, where it settles and is eaten by microorganisms, which are in turn eaten by fish.

In the US, mercury levels in the environment have been increasing at a rate of 1.5% each year since 1970. And in at least forty states, mercury contamination has reached such high levels that state officials are advising residents to limit their consumption of fish from their entire state, or from one or more bodies of water within their state.

Mercury is very hazardous for humans and eating fish contaminated with mercury can result in serious health problems, including heart disease and damage to the brain and nervous system. This is of particular concern to growing children and pregnant women. Complicating this issue is that scientists are not certain how much mercury-tainted fish is needed to trigger health problems.

A recent report by the Research Institute of Public Health in Finland shows a significant increase of heart disease in men with elevated mercury levels. (9) Since seafood in the diet is the main source of human mercury exposure, men eating swordfish, shark, and tuna high in mercury may unknowingly be increasing their risk of an early death.

Recent research on mercury in the USA

Recent research in the US, presented by Dr Jane Hightower at a symposium of environmental health experts in Vermont, is one of the first studies to document mercury levels in Americans who eat more fish than the Environmental Protection Agency recommends.

Hightower screened 720 people from March 2000 to March 2001, then tested the mercury levels of those who reported eating more than two servings of fish a week. That's the maximum the EPA recommends for pregnant women and small children.

The tests showed that of 116 people who had their blood tested, 89% showed mercury levels greater than the 5 parts per million recognized as safe by the National Academy of Sciences. Of that group, 63 people had blood mercury levels more than twice the recommended level and 19 showed blood mercury levels four times the level considered safe. Four people had mercury levels 10 times as high as the government recommends.

About 78% of those surveyed with high mercury levels reported eating canned tuna more than three times a month; 74% ate salmon more than four times a month; and 72% said they had swordfish more than once a month. Other fish commonly eaten by respondents included halibut, ahi, sea bass and sushi.

PCBs (Polychlorinated Biphenyls)

PCBs (Polychlorinated Biphenyls), once widely used for industrial purposes but outlawed as carcinogenic in 1976, can also be found in fish due to environmental contamination. According to a six-month investigation by the Consumers Union in the US (publishers of Consumer Reports magazine), "By far the biggest source of PCBs in the human diet is fish... As PCBs linger in the environment, their composition changes, and they gradually become more toxic... And these more toxic forms are likely to be found in fish... PCBs accumulate in body tissue. The PCBs that you eat today will be with you decades into the future." (10)

Fisheries in crisis
By-catch - an incredible waste
Case study: Tuna fishing and dolphins
The impacts of fishing on other animals
Commercial fishing
  Purse seine nets
  Drift nets
  Longline fishing
  Bottom trawling
Technology opens oceans to trawling
Trawling destroys vital habitat
Recent improvements in design
Fish Farming
Recreational fishing
   VNPA research review
   CSIRO Port Phillip Bay Study 1999
Fish and pain
Fish and intelligence
Fish and human health
   Omega-3 Essential Fatty Acids
  A lot of fat and cholesterol, and no fibre
  Bio-accumulation of toxic chemicals
  Recent research on mercury in the USA
   PCBs (Polychlorinated Biphenyls)
   Food poisoning risk
Recent fishing issues (news articles)
Links of Interest
Next ..


Marine and Atmospheric Research


   Contact Web Manager © MESA 1999 - 2010
0.00000 secs   
  BriTer Solutions   SpiderByte Web Design Top