Fish and shellfish are low in total and saturated fat content and they are excellent sources of protein and vitamins, so you should try to include them in your diet at least twice a week. They also are high in important nutrients, such as vitamins B1, B6, D and niacin, and some are rich in omega-3 fatty acids.

oil rich fish as salmon, mackerel and sardines contain a healthy fat called omega-3 fatty acids. This fat is believed to reduce the risk of your developing cardiovascular disease by increasing the levels of good cholesterol in the body and lowering the levels of bad cholesterol and triglycerides.

Omega-3 fatty acids have also found to prevent blood clots by making platelets less likely to clump together and stick to artery walls. Blood vessels are also less likely to construct, making the heart less vulnerable to life threatening irregular heart rates. Omega-3 help relieve the symptoms of arthritis and people who regularly consume oil rich fish are less likely to suffer from depression.

All fish and shellfish contain some omega-3 fatty acids in different amount. The fatter fish contain more than the leaner fish, but the proportion of omega-3 fatty acids can vary considerably between fish species. The amount of omega-3 fatty acids in farm raised seafood can also vary depending on the diet that the fish or shellfish are fed.

  Oily fish: Oily fish like mackerel, salmon, tuna have more than 5% fat (mostly omega-3) in their flesh. All omega-3 fats are essential for healthy cells, brain development, cognitive function and general good health. As well as offering vitamin D, canned sardines is an excellent source of calcium as you can eat the bones. Canned tuna contains much less vitamin D and essential fatty acid than the fresh fish as its oil is removed before canning and is sold separately. Avoid fish canned in vegetable oil as this blend may contain a lot of saturated fat. Only buy fish that has been canned in olive, sunflower or soya-bean oil. If you suffer from any other forms of arthritis, however, you will find oily fish extremely helpful as they have a potent anti-inflammatory action, which can relieve joint and muscle pains.
 White Fish: They all contain virtually no fat, few calories and plenty of protein as well as the B vitamins. They don't however, contain much iron and though halibut, which is slightly oily, may contribute a little vitamin A, the white fish do not generally supply fat-soluble vitamins. The livers of cod and halibut are very rich in vitamins A, D and E, but these aren't eaten, only used for the production of oil. The roe of white fish is an excellent source of B vitamins and as a good source of iron and some meat, but fish roe contains cholesterol so may not be suitable for people with inherited disorders of fat metabolism or very high cholesterol levels.
Shellfish, which are divided into: mollusks (small, soft-bodied sea animals which live inside a hard shell) e.g mussel; crustaceans (soft-bodied, jointed sea animals which are covered by a hard protective "crust" or external skeleton), e.g lobster, crap, shrimp.

Benefits of fish and shellfish

Fish is an excellent source of protein, calcium and minerals such as phosphorus, iron, selenium, potassium and vitamins including thiamine, riboflavin, and niacin, which are all important for achieving and maintaining good health
Shellfish can also contribute to a healthy, balanced diet. Shellfish species like mussels, clams, scallops, shrimp, oysters, lobster and abalone are low in calories and saturated fats, are also excellent sources of protein and contain omega-3 fatty acids. Like fish, shellfish contribute to health by providing essential minerals and vitamins such as iron, zinc and copper and vitamin B 12.
Fish is now the preferred food of people who wants to stay healthy, white fish in particular is more easily digested than meat, therefore it is ideally for people with digestive problems. Unlike meat, the fat in fish consists mostly of oils containing unsaturated fatty acids. The essential fatty acids in oily fish are of benefits to health.

Good for the Heart, Brain and Waistline

There are many benefits to eating fish on a regular basis, whether they are wild or farmed. Studies show that people who eat fish at least once per week significantly lower their risk of heart disease and stroke. Furthermore, there is evidence that fish is beneficial for developing the fetal and infant brain.
Who eat diet based on fish, have low incidence of cardiovascular disease, the link between eating fish and reduced risk of heart attack has been a hot  topic. Research confirms that eating fish even a few times per month, can help to reduce your risk of developing cardiovascular disease.

Shellfish has acquired a bad reputation because some shellfish contain a high level of cholesterol. We know that cholesterol levels in the blood are related to the intake of saturated fat rather than to eating cholesterol rich foods. Since more shellfish are very low in total fat, there is no reason to exclude them from your diet, particularly if you choose them over higher fat red meat. Be sure, though, to use low-fat cooking and grilling rather than frying.

Fish and shellfish are as safe to eat as any other source of protein. Most harmful microbes found in fish are destroyed during cooking. Women who are pregnant or intending to become pregnant, or who are breast feeding are advised to avoid eating any fish known to contain high levels of mercury. This is because mercury can affect the baby's developing nervous system. Swordfish, shark and marlin contain high levels of mercury. Tuna doesn't have as high a content as these fish, but it contain more mercury than fish such as cod, haddock, salmon and plaice. So the advice is to limit the amount of tuna eating. 

Fish and shellfish are excellent sources of protein that are low in fat. A 3-ounce cooked serving of most fish and shellfish provides about 20 grams of protein, or about a third of the average daily recommended protein intake. The protein in fish is of high quality, containing an abundance of essential amino acids, and is very digestible for people of all ages. Seafood is also generally lower in fat and calories than beef, poultry or pork. Seafood is also loaded with minerals such as iron, zinc and calcium (canned fish with soft, edible bones).

How to choose fish: As fresh fish deteriorates rapidly, it is important to choose it carefully. Fresh fish should have:
- Bright eyes and shiny, not sunken.
- Plump, firm flesh
- Plenty of bright scales, firmly attached to the skin
- Moist skin
- A fresh, sea smell
- Bright red gills, not sunken

How to choose shellfish: When buying shellfish check that they feel heavy for their size. All mollusks should be closed and all shellfish should be eaten on the day you buy them. Above all, buy your shellfish from a supplier whose reputation you can rely on.

Cooking Fish: Fish has a muscle composition similar to that of meat, but there is far less connective tissue, so it is much easier to tenderize and quicker to cook. It is important not to overcook fish as the protein easily becomes tough and the flesh dry. The muscle is formed into flakes which separate on cooking. The best ways to cook fish are baking, steaming, grilling, or pan-frying in shallow oil, as all these methods minimize the loss of nutrients. Boiling fish results in considerable loss of minerals, especially iodine, but as long as you use the cooking water to make sauce for your fish dish, you won't lose out.

Storage: Fish should be eaten as soon as possible after purchase, and should be stored in the coldest part of the refrigerator (but not the ice box), well wrapped, to prevent the strong odors from contaminating other foods.