1. Nutritional aspects

2. Why do consumers buy fish?
Tasty
Convenient
Good value
Healthy and nutritious

3. Health and seafood Seen as healthy option Good source of protein
Low-fat no fat
Source of the Omega 3 fatty acids
Oily fish contain n-3 fatty acids (also known as omega-3 fatty acids) and vitamins A and D.

4. perceptions of health vary with seafood categories
More Healthy
Less Healthy
Oil rich fish
Shellfish
Fresh
Processed
White fish
Frozen
Natural

5. Composition of fish Lean fish e.g. Cod Water 78 – 83% Protein 15 - 20%
Fat %
Fatty fish e.g. Mackerel
Water %
Protein %
Fat %

6. Fish muscle
The diagram of a cod fillet shows the surface that was adjacent to the skeleton; the mechanical construction shown here is typical of all white fish, that is fish in which the fat is confined mainly to the liver. The blocks of muscle, which form the individual flakes in the cooked fish, are separated by thin sheets of what is known as connective tissue; these are curved within the fillet and run from the backbone to the skin. In fresh fish the muscle blocks are firmly attached to the connective tissue, and the surface of a cut fillet is smooth and continuous. There are also tiny blood vessels running through the muscle. The connective tissue accounts for only a small percentage of the total weight of the muscle, smaller than for example in beef muscle; this is one reason why fish is generally less tough to eat than meat.
See next slide.
Fish muscle is of two kinds, light muscle and dark muscle. In white fish such as cod and haddock there is a small strip of dark, or red, muscle just under the skin on both sides of the body, running beneath the lateral line. In fatty fish such as herring and mackerel the strips of dark muscle are much larger in proportion and contain higher concentrations of fat and certain vitamins. Since it is not usually practicable to separate the dark, fatty muscle from the light muscle when preparing fish for cooking, as one might trim fat from beef for example, the values given in the tables for composition of flesh are for the total muscle, taking light and dark together.

7. Cross section through body of fish
Fish muscle is of two kinds, light muscle and dark muscle. In white fish such as cod and haddock there is a small strip of dark, or red, muscle just under the skin on both sides of the body, running beneath the lateral line. In fatty fish such as herring and mackerel the strips of dark muscle are much larger in proportion and contain higher concentrations of fat and certain vitamins. Since it is not usually practicable to separate the dark, fatty muscle from the light muscle when preparing fish for cooking, as one might trim fat from beef for example, the values given in the tables for composition of flesh are for the total muscle, taking light and dark together.

8. Water 70 – 80% weight of white fish fillet 70% of fatty fish fillet
The main constituent of fish flesh is water, which usually accounts for about 80 per cent of the weight of a fresh white fish fillet. Whereas the average water content of the flesh of fatty fish is about 70 per cent, individual specimens of certain species may at times be found with a water content anywhere between the extremes of 30 and 90 per cent.
The water in fresh fish muscle is tightly bound to the proteins in the structure in such a way that it cannot readily be expelled even under high pressure. After prolonged chilled or frozen storage, however, the proteins are less able to retain all the water, and some of it, containing dissolved substances, is lost as drip. Frozen fish that are stored at too high a temperature, for example, will produce a large amount of drip and consequently quality will suffer. In the living fish, the water content usually increases and the protein content decreases as spawning time approaches; thus it is possible, with cod for example, to estimate the condition of the fish by measuring the water content of the muscle.
In cod, the water content of the muscle is slightly higher at the tail than at the head; this slight but consistent increase from head to tail is balanced by a slight reduction in protein content.

9. Protein 15 to 20 % of body weight Amino acids: lysine methionine
found in high concentrations
complement cereal protein in diet.
The amount of protein in fish muscle is usually somewhere between 15 and 20 per cent, but values lower than 15 per cent or as high as 28 per cent are occasionally met with in some species.
All proteins, including those from fish, are chains of chemical units linked together to make one long molecule. These units, of which there are about twenty types, are called amino acids, and certain of them are essential in the human diet for the maintenance of good health. Furthermore, if a diet is to be fully and economically utilized, amino acids must not only be present but must also occur in the correct proportions. Two essential amino acids called lysine and methionine are generally found in high concentrations in fish proteins, in contrast to cereal proteins for example. Thus fish and cereal protein can supplement each other in the diet. Fish protein provides a good combination of amino acids which is highly suited to man’s nutritional requirements and compares favourably with that provided by meat, milk and eggs.

10. Fat Not distributed evenly throughout the flesh of the fish.
Concentrated in dark muscle of fatty fish.
Taking all species into account, the fat content of fish can vary very much more widely than the water, protein or mineral content. Whilst the ratio of the highest to the lowest value of protein or water content encountered is not more than three to one, the ratio between highest and lowest fat values is more than 300 to one.
The term fat is used for simplicity throughout this leaflet, although the less familiar term lipid is more correct, since it includes fats, oils and waxes as well as more complex, naturally-occurring compounds of fatty acids.
There is usually considerable seasonal variation in the fat content of fatty fish; for example a starved herring may have as little as ½ per cent fat, whereas one that has been feeding heavily to replenish tissue may have a fat content of over 20 per cent. Sardines, sprats and mackerel also exhibit this seasonal variation in fat content. As the fat content rises, so the water content falls, and vice versa; the sum of water and fat in a fatty fish is fairly constant at about 80 per cent. Although protein content falls very slightly when the fat content falls, it nevertheless remains fairly constant, somewhere between 15 and 18 per cent.
The fat is not always uniformly distributed throughout the flesh of a fatty fish. For example in Pacific salmon there may be nearly twice as much fat in muscle from around the head as there is in the tail muscle.
In white fish of the cod family, the fat content of the muscle is always low, usually below 1 per cent, and seasonal fluctuations in fat content are noticeable mainly in the liver, where the bulk of the fat is stored.

11. Fish oil Extracted from whole fish
High in poly unsaturated fatty acids
Used for:
Margarines and shortenings
Fish liver oils were used in the treatment of rickets as early as the Middle Ages. Certain fish liver oils were prescribed as a cure for night-blindness. Both rickets and night-blindness are largely caused by a dietary deficiency in vitamins A and D, both of which are found in certain fish livers in various proportions.
For Atlantic cod (Gadus morhua), the weight of its liver can fluctuate with season, fishing ground and condition of the fish. The weight of livers ranges from 2% to 7% of whole, ungutted fish with an average value of 5%, or, from 3% to 8% of gutted fish with an average value of 5% (Waterman, 1964).
The composition of cod livers also varies. A typical range of proximate analysis values is: 27 – 32% moisture content,
5 – 7% protein content,
55 – 65% oil content
and 0 – 4% ash content

12. Fish oil 2 Extracted from fish liver Cod liver oil Vitamin A Vitamin D
Omega-3 fatty acids (EPA and DHA).
Cod liver oil is made by cooking cod livers with steam and then cooling to -5 oC pressing/decanting the cooked livers to extract the oil. Fish oils are extracted from the cooked whole body tissues of fatty fish during the manufacture of fish meal. Cod liver oil and fish oil are similar but have a somewhat different composition: fish oil has a much lower content of vitamins A and D compared to liver oils.
See Extras Cod Liver Oil

13. The minor components of fish muscle
Carbohydrates
Minerals and Vitamins
The amount of carbohydrate in white fish muscle is generally too small to be of any significance in the diet; hence no values are given in the tables. In white fish the amount is usually less than 1 per cent, but in the dark muscle of some fatty species it may occasionally be up to 2 per cent. Some molluscs, however, contain up to 5 per cent of the carbohydrate glycogen.
Minerals and Vitamins include a range of substances widely different in character that must be present in the diet, even if only in minute quantities, not only to promote good health but also to maintain life itself.
Although fish is very unlikely to be the only source of an essential mineral in the diet, fish does provide a well balanced supply of minerals in a readily usable form.
Vitamins can be divided into two groups, those that are soluble in fat, such as vitamins A, D, E and K, and those that are soluble in water, such as vitamins B and C. All the vitamins necessary for good health in humans and domestic animals are present to some extent in fish, but the amounts vary widely from species to species, and throughout the year.
The vitamin content of individual fish of the same species, and even of different parts of the same fish, can also vary considerably. Often the parts of a fish not normally eaten, such as the liver and the gut, contain much greater quantities of oil-soluble vitamins than the flesh; the livers of cod and halibut for example contain almost all of the vitamins A and D present in those species. In contrast, the same two vitamins in eels, for example, are present mainly in the flesh.
Water-soluble vitamins in fish, although present in the skin, the liver and gut, are more uniformly distributed, and the flesh usually contains more than half the total amount present in the fish. The roe, when present, is also a good source of these vitamins.
In general the vitamin content of white fish muscle is similar to that of lean meat and, with the exception of vitamin C, can usually make a significant contribution to the total vitamin intake of man and domestic animals.
The mineral and vitamin content of fish is not markedly affected by careful processing or by preservation, provided storage is not very prolonged.

14. Mercury in Fish Bad fish, good fish
Fish most likely to contain mercury:
• Shark • Swordfish • King mackerel • Tilefish • Albacore tuna
Fish known to be low in mercury:
• Shrimp • Canned light tuna • Salmon • Pollock • Catfish
Source: FDA/EPA
The U.S. Food and Drug Administration has issued formal guidelines warning about the mercury content in certain kinds of fish, particularly for infants and children — a position the state Department of Health took last year based on the same evidence.
But both government agencies continue to stress that many seafoods are low in mercury and that fish is a healthy food, a good source of protein and other nutrients. The National Fisheries Institute, a trade association, also cited the health benefits of fish. The organization expressed concern that the guidelines might alarm consumers and cause them to avoid fish.
"The concern is that there could be a mental effect on a young child," said Lester Crawford, deputy commissioner of the Food and Drug Administration. While mercury can affect many organs, the brain is the most sensitive, he said.
The USDA said certain fish — notably shark, swordfish, king mackerel and albacore tuna — contain higher levels of mercury and should be avoided by small children and women who are pregnant, likely to become pregnant or breast feeding. Shrimp, canned light tuna, salmon, pollock and catfish are safer, the agency said.
Hawai'i officials looked at mercury data and sought and received an exemption last year that allowed it to replace tuna with salmon in a program for breast-feeding women in low-income families.
"We made a request to let our clients elect canned salmon instead of canned tuna. Hawai'i was the first state to get that granted," said Sue Uyehara, program support section chief for the state Department of Health Women Special Supplemental Nutrition Program for Women, Infants and Children (WIC).
The program also created a brochure, "A Local Guide to Eating Fish Safely," available on the Health Department Web site at
The brochure notes that fish higher on the food chain can have higher levels of mercury, since they build up in their tissues the mercury from smaller fish they eat, which absorb mercury from the water.
"This is an important story. Good for the USDA for finally making these guidelines," said Sher Pollack, WIC quality assurance coordinator.
The Health Department divides fish into three categories based on likely mercury levels.
It recommends that top predators such as 'ahi, ono and opah be eaten no more than once every two weeks; fish to be eaten no more than weekly include aku (skipjack tuna), mahi-mahi, canned tuna, nairagi (striped marlin), cod, grouper, orange roughy, pollock and halibut. Akule, awa, moi, mullet, salmon, ika (squid), tako (octopus), scallops and shrimp generally can be eaten anytime.
Hawai'i physician Dr. Terry Shintani, author of "Hawai'i Diet" and "The Good Carbohydrate Revolution," recommends that fish be eaten far less often.
"Optimally, most people should eat fish rarely. That doesn't mean people should eat more chicken and meat. They are no more free of contaminants — just different.
"To me, a plant-based diet is the healthiest. These contaminants don't bioaccumulate in plants," Shintani said.
Fish consumption has been promoted in recent years because the food contains omega-3 fatty acids, which can be good for the heart. The American Heart Association recommends eating fish at least twice weekly, and more often if you are diagnosed with heart disease.
The response of the USDA and the Environmental Protection Agency — which joined the USDA in making the recommendations — follows that of the Hawai'i Department of Health, emphasizing fish lowest in mercury. The federal guidelines suggest two meals weekly of a low-mercury fish, for a weekly intake totaling 12 ounces.
"By following these guidelines, we're confident that women and young children can safely include fish as an important part of a healthy diet," Crawford said.
Reach Jan TenBruggencate at

15. Factors affecting the composition of fish
Fishing ground
Season
Food supply
The composition of a particular species often appears to vary from one fishing ground to another, and from season to season, but the basic causes of change in composition are usually variation in the amount and quality of food that the fish eats and the amount of movement it makes. For example, fish usually stop feeding before they spawn, and draw on their reserves of fat and protein. Again, when fish are overcrowded, there may not be enough food to go round; intake will be low and composition will change accordingly. Reduction in a basic food resource, plankton for example, can affect the whole food chain. An example of how abundance of food supply can markedly change the composition of a species is shown by the sheepshead, an American freshwater fish: when taken from certain small lakes that were overstocked, the sheepshead had an average fat content of 1 per cent, compared with 6-10 per cent for those taken from rivers or lakes where food was plentiful.