INTRODUCTION TO FISH AND HEALTH
Fish and shellfish are one of the first foods that our ancient ancestors hunted for their dinners. In fact, lots of early human communities were based around the coastlines of seas and oceans because of the abundance of marine food. Nowadays, this abundance of fish is extremely reduced - it is so bad that some fish species are on the verge of extinction due to the high commercial fishing in combination with modern technology that makes fishing even more efficient. As a result, we see some fish come and go in the shops, e.g. monkfish: sometimes it's available, sometimes it's not. Somehow, the unbalanced state of nature has been countered with the invention of fishing farms, yet the natural fishing is not discontinued. It is estimated that about 70% of the fish species that we consume are harvested beyond the rate of their natural ability to sustain themselves. Farmed fish, on the other hand, can be grown en masse, and their meat is moist and succulent, sometimes even more than the line-caught fish. This is because their exercise and food can be controlled by the farmers. For now, we have many fish species in farms all over the world, and we can enjoy salmon, sea bass, or rainbow trout in fairly high amounts. However, fish farming is not meaning just advantages. They usually don't taste as much as the wild fish. In addition, the use of antibiotics and artificial food affects the surrounding water environments. Some toxins released by industry also find an easy way to the near-coast fish farms, and we know that farmed salmon is a big collector of PCB - an environmental toxin that damages liver and reproductive organs, and may cause cancer. Fish are also common carriers of bacteria or parasites, so they have to be cooked properly to minimize the risk of being struck by a food-borne disease. We certainly hope that the state of the above discussed matter will change for the better, but for now let's consider the fish as an ingredient in our cooking.
(For a scientific discursion on the above problem, look in Myers, Ransom A. and Worm, Boris. "Rapid worldwide depletion of predatory fish communities." Nature 423, 280-283).
Fish is healthy food. Especially fish oils are known health promoters. Fish also have B vitamins and carry the marine abundance of iodine. They are not very fat either, and if they are, the fats are usually healthy (e.g. salmon) although they may contain some fat-soluble toxins. Therefore, it is a good practice to always take some time and find out where your fish is coming from. It is worth it, because sea fish fat often contains omega-3 fatty acids. (Freshwater fish don't have much omega-3 because they don't eat the oceanic plankton.) Omega-3 are known to reduce the bad cholesterol in our blood, which is now considered to be be the major cause of death in our western civilization. Omega-3 are also necessary for a proper function of our nervous system, including the brain! They can also, as if it were not enough, reduce the excessive inflammatory response in our bodies, so the risk getting cardiovascular problems or cancer is diminished.
Fish is not only healthy, it can also be dangerously unhealthy. As mentioned above, lots of environmental toxins that are released into waters by industries and households are easily taken up by fish. Most toxins can be found in the predatory fish high up in the food chain (biomagnification). Usually, the further away from the coast, the less toxins are there in the fishes. So, any PCBs, heavy metals (mercury, cadmium), and other dangerous waste is more concentrated in lakes and near the oceanic coastlines. In some areas, the authorities advise against eating certain sorts of fish, usually high-fat species like salmon or carp. These are the ones that accumulate most fat-soluble toxins that damage our nervous system and contribute to cancer. But nowadays, even some oceanic fishes are so heavily contaminated that it is unwise to eat them, at least on a frequent basis. Tuna and swordfish, the very popular duo, belong to this category. What is best to eat? Fish that are small, have a short life span, and are grown up in farms with controlled water supply have normally the least contaminants. So, fish like sole, mackerel, some salmons, or sardines are the more healthy bet. Of course, we don't have to close out the other fishes forever, from time to time we can enjoy the taste of a swordfish or sea bass, but not too often (unfortunately).
Food from the sea also carries dangerous bacteria or viruses, as well as parasites. Or at least, the potential to obtain an infected fish or shellfish is high. Therefore, it is important to cook the fish thoroughly to kill any possible threats to our health. However, some bacteria, even though they are killed, can still leave behind some dangerous chemicals. Of the most known, cholera and botulism bacteria are the ones that may cause problems. The threats are especially common in raw seafood. For example, some oysters may contain a deadly form of Vibrio bacteria. It is therefore best to buy oysters from trustable sources and maybe to minimize their consumption as far as possible.
Even if some toxins are denatured during cooking, others remain their toxic activity despite the heat. Some mackerels, tunas, herrings, sardines or anchovies can contain bacteria that cause food poisoning resulting in nausea and diarrhoea. Other toxins, found in shellfish (mussels, clams, oysters, scallops), come from the food of the seafood - the algae. As you may know, some algae release toxins that can affect our nervous system and they might even kill. Other algae poisonings can cause diarrhoea or paralysis. It all depends on what kind of food our seafood has eaten itself.
Besides bacteria and viruses, and their toxins, fish can also be infected with small worms (parasites). usually, they don't present a problem if we cook the fish thoroughly. Parasites also die when we freeze them for about a week (unlike bacteria who survive!). Some of the commonest parasites attack our throats and gastrointestinal tract, and can cause nausea and diarrhoea. They can be found in almost any fish. Parasites like cod worms, tapeworms, or flatworms are not uncommon and so the cooking of the fish should be done properly.
Then, even if we happen to get a perfectly healthy fish, we can still make it health-deteriorating by applying too much direct heat to it. Frying or grilling, even though tasty, can create some carcinogenic compounds in the fish (as well as in the meat). So, minimize these techniques, or don't overdo them. Also, it is best to poach or bake the fish and meat rather than frying them over high dry heat.
Fish tastes amazing, but only if they are properly taken care of and properly cooked. What makes fish more complex than meat is their wide variety and fragility. This is what we have to account for when we prepare fish! And we will do that in this and other articles on fish.