4.1. Principal constituents
4.2. Lipids
4.3. Proteins
4.4. N-containing extractives
4.5. Vitamins and minerals

4.1 Principal constituents

The chemical composition of fish varies greatly from one species and one individual to another depending on age, sex, environment and season.

The principal constituents of fish and mammals may be divided into the same categories, and examples of the variation between the constituents in fish are shown in Table 4.1. The composition of beef muscle has been included for comparison.

Table 4.1 Principal constituents (percentage) of fish and beef muscle


Fish (fillet)

Beef (isolated muscle)



Normal variation


























SOURCES: Stansby, 1962; Love, 1970

As can be seen from Table 4.1, a substantial normal variation is observed for the constituents of fish muscle. The minimum and maximum values listed are rather extreme and encountered more rarely.

The variation in the chemical composition of fish is closely related to feed intake, migratory swimming and sexual changes in connection with spawning. Fish will have starvation periods for natural or physiological reasons (such as migration and spawning) or because of external factors such as shortage of food. Usually spawning, whether occurring after long migrations or not, calls for higher levels of energy. Fish having energy depots in the form of lipids will rely on this. Species performing long migrations before they reach specific spawning grounds or rivers may utilize protein in addition to lipids for energy, thus depleting both the lipid and protein reserves, resulting in a general reduction of the biological condition of the fish. Most species, in addition, do usually not ingest much food during spawning migration and are therefore not able to supply energy through feeding.

During periods of heavy feeding, at first the protein content of the muscle tissue will increase to an extent depending upon how much it has been depleted, e.g., in relation to spawning migration. Then the lipid content will show a marked and rapid increase. After spawning the fish resumes feeding behaviour and often migrates to find suitable sources of food. Plankton-eating species such as herring will then naturally experience another seasonal variation than that caused by spawning, since plankton production depends on the season and various physical parameters in the oceans.

The lipid fraction is the component showing the greatest variation. Often, the variation within a certain species will display a characteristic seasonal curve with a minimum around the time of spawning. Figure 4.1 shows the characteristic variations in the North Sea herring (4.1a) and mackerel (4.1b).


Figure 4.1 Seasonal variation in the chemical composition of (a) herring fillets (Clupea harengus) and (b) mackerel fillets (Scomber scombrus). Each point indicates the mean value of eight fillets

Although the protein fraction is rather constant in most species, variations have been observed such as protein reduction occuring in salmon during long spawning migrations (Ando et al., 1985 b; Ando and Hatano, 1986) and in Baltic cod during the spawning season, which for this species extends from January to June/July (Borresen, 1992). The latter variation is illustrated in Figure 4.2.


Figure 4.2 Variation in percentage dry matter in muscle of Baltic cod Vertical bars represent standard deviation of the mean value. (Borresen, 1992)

Some tropical fish also show a marked seasonal I variation in chemical composition. West African shad (Ethmalosa dorsalis) shows a range in fat content of 2-7 % (wet weight) over the year with a maximum in July (Watts, 1957). Corvina (Micropogon furnieri) and pescada-foguete(Marodon ancylodon) captured off the Brazilian coast had a fat content range of 0.2-8.7 % and 0.1-5.4 % respectively (Ito and Watanabe, 1968). It has also been observed that the oil content of these species varies with size, larger fish containing about 1 % more oil than smaller ones. Watanabe (1971) examined freshwater fish from Zambia and found a variation from 0.1 to 5.0 % in oil content of four species including both pelagics and demersals.

A possible method for discriminating lean from fatty fish species is to term fish that store lipids only in the liver as lean, and fish storing lipids in fat cells distributed in other body tissues as fatty fish. Typical lean species are the bottom-dwelling ground fish like cod, saithe and hake. Fatty species include the pelagics like herring, mackerel and sprat. Some species store lipids in limited parts of their body tissues only, or in lower quantities than typical fatty species, and are consequently termed semi- fatty species (e.g., barracuda, mullet and shark).

The lipid content of fillets from lean fish is low and stable whereas the lipid content in fillets from fatty species varies considerably. However, the variation in the percentage of fat is reflected in the percentage of water, since fat and water normally constitute around 80 % of the fillet. As a rule of thumb, this can be used to estimate the fat content from an analysis of the amount of water in the fillet. In fact, this principle is being utilized with success in a fat-analysing instrument called the Torry Fish Fat Meter, where it is the water content that is actually being measured (Kent et al., 1992).

Whether a fish is lean or fatty the actual fat content has consequences for the technological characteristics postmortem. The changes taking place in fresh lean fish may be predicted from knowledge of biochemical reactions in the protein fraction, whereas in fatty species changes in the lipid fractions have to be included. The implication may be that the storage time is reduced due to lipid oxidation, or special precautions have to be taken to avoid this.

The variations in water, lipid and protein contents in various fish species are shown in Table 4.2.

Table 4.2 Chemical composition of the fillets of various fish species

Species Scientific name Water % Lipid % Protein % Energy value(kJ/ 100 g)
Blue whiting a) Micromesistius poutassou 79-80 1.9-3.0 13.8-15.9 314-388
Cod a) Gadus morhua 78-83 0.1-0.9 15.0-19.0 295-332
Eel a) Anguilla anguilla 60-71 8.0-31.0 14.4  
Herring a) Clupea harengus 60-80 0.4-22.0 16.0-19.0  
Plaice a) Pleuronectes platessa 81 1.1-3.6 15.7-17.8 332-452
Salmon a) Salmo salar 67-77 0.3-14.0 21.5  
Trout a) Salmo trutta 70-79 1.2-10.8 18.8-19.1  
Tuna a) Thunnus spp. 71 4.1 25.2 581
Norway lobster a) Nephrops norvegicus 77 0.6-2.0 19.5 369
Pejerrey b) Basilichthys bornariensis 80 0.7-3.6  17.3-17.9  
Carp b) Cyprinus carpio 81.6 2.1 16.0  
Sabalo c) Prochilodus platensis 67.0 4.3 23.4  
Pacu c) Colossoma macropomum 67.1 18.0 14.1  
Tambaqui c) Colossoma brachypomum 69.3 15.6 15.8  
Chincuiña c) Pseudoplatystoma tigrinum 70.8 8.9 15.8  
Corvina c) Plagioscion squamosissimus 67.9 5.9 21.7  
Bagré c) Ageneiosus spp. 79.0 3.7 14.8  

SOURCES: a) Murray and Burt, 1969, b)Poulter and Nicolaides, 1995 a. c) Poulter and Nicolaides, 1985 b

The carbohydrate content in fish muscle is very low, usually below 0.5 %. This is typical for striated muscle, where carbohydrate occurs in glycogen and as part of the chemical constituents of nucleotides. The latter is the Source of ribose liberated as a consequence of the autolytic changes post mortem.

As demonstrated above, the chemical composition of the different fish species will show variation depending on seasonal variation, migratory behaviour, sexual maturation, feeding cycles, etc. These factors are observed in wild, free-living fishes in the open sea and inland waters. Fish raised in aquaculture may also show variation in chemical composition, but in this case several factors are controlled, thus the chemical composition may be predicted. To a certain extent the fish farmer is able to design the composition of the fish by selecting the farming conditions. It has been reported that factors such as feed composition, environment, fish size, and genetic traits all have an impact on the composition and quality of the aquacultured fish (Reinitz et al., 1979).

The single factors having the most pronounced Impact on the chemical composition is considered to be the feed composition. The fish farmer is interested in making the fish grow as fast as possible on a minimum amount of feed, as the feed is the major cost component in aquaculture. The growth potential is highest when the fish is fed a diet with a high lipid content for energy purposes and a high amount of protein containing a well balanced composition of amino acids.

However, the basic metabolic pattern of the fish sets some limits as to how much lipid can be metabolized relative to protein. Because protein is a much more expensive feed ingredient than lipid, numerous experiments have been performed in order to substitute as much protein as possible with lipids. Among the literature that may be consulted is the following: Watanabe et al., 1979; Watanabe, 1982; Wilson and Halver, 1986; and Watanabe et al., 1987.

Usually most fish species will use some of the protein for energy purposes regardless of the lipid content. When the lipid content exceeds the maximum that can be metabolized for energy purposes, the remainder will be deposited in the tissues, resulting in a fish with very high fat content. Apart from having a negative impact on the overall quality, it may also decrease the yield, as most surplus fat will be stored in depots in the belly cavity, thus being discarded as waste after evisceration and filleting.

A normal way of reducing the fat content of aquacultured fish before harvesting is to starve the fish for a period. It has been demonstrated for both fatty and lean fish species that this affects the lipid content (see, e.g., Reinitz, 1983;Johansson and Kiessling, 1991; Lie and Huse, 1992).

It should be mentioned that in addition to allowing for the possibility of, within certain limits, predetermining the fish composition in aquaculture operations, keeping fish in captivity under controlled conditions also offers the possibility of conducting experiments in which variation in chemical composition observed in wild fish may be provoked. The experiments may be designed such that the mechanisms behind the variations observed in wild fish may be elucidated.

4.2 Lipids

The lipids present in teleost fish species may be divided into two major groups: the phospholipids and the triglycerides. The phospholipids make up the integral structure of the unit membranes in the cells; thus, they are often called structural lipids. The triglycerides are lipids used for storage of energy in fat depots, usually within special fat cells surrounded by a phospholipid membrane and a rather weak collagen network. The triglycerides are often termed depot fat. A few fish have wax esters as part of their depot fats.

The white muscle of a typical lean fish such as cod contains less than 1 % lipids. Of this, the phospholipids make up about 90 % (Ackman, 1980). The phospholipid fraction in a lean fish muscle consists of about 69 % phosphatidyl-choline, 19 % phosphatidyl-ethanolamine and 5 % phosphatidyl-serine. In addition, there are several other phospholipids occurring in minor quantities.

The phospholipids are all contained in membrane structures, including the outer cell membrane, the endoplasmic reticulum and other intracellular tubule systems, as well as membranes of the organelles like mitochondria. In addition to phospholipids, the membranes also contain cholesterol, contributing to the membrane rigidity. In lean fish muscle cholesterol may be found in a quantity of about 6 % of the total lipids. This level is similar to that found in mammalian muscle.

As already explained, fish species may be categorized as lean or fatty depending on how they store lipids for energy. Lean fish use the liver as their energy depot, and the fatty species store lipids in fat cells througout the body.

The fat cells making up the lipid depots in fatty species are typically located in the subcutaneous tissue, in the belly flap muscle and in the muscles moving the fins and tail. In some species which store extraordinarily high amounts of lipids the fat may also be deposited in the belly cavity. Depending on the amount of polyunsaturated fatty acids, most fish fats are more or less liquid at low temperature.

Finally, fat depots are also typically found spread throughout the muscle structure. The concentration of fat cells appears to be highest close to the myocommata and in the region between the light and dark muscle (Kiessling et al., 1991). The dark muscle contains some triglycerides inside the muscle cells even in lean fish, as this muscle is able to metabolize lipids directly as energy. The corresponding light muscle cells are dependent on glycogen as a source of energy for the anaerobic metabolism.

In dark muscle the energy reserves are completely catabolized to CO2 and water, whereas in light muscle lactic acid is formed. The mobilization of energy is much faster in light muscle than in dark muscle, but the formation of lactic acid creates fatigue, leaving the muscle unable to work for long periods at maximum speed. Thus, the dark muscle is used for continuous swimming activities and the light muscle for quick bursts, such as when the fish is about to catch a prey or to escape a predator.

An example of the seasonal variation in fat deposition in mackerel and capelin is shown in Figure 4.3, where it is seen that the lipid content in the different tissues varies considerably. The lipid stores are typically used for long spawning migrations and when building up gonads (Ando et al., 1985 a). When the lipids are mobilized for these purposes there are questions as to whether the different fatty acids present in the triglyceride are utilized selectively. This is apparently not the case in salmon, but in cod a selective utilization of C22:6 has been observed (Takama et al., 1985).


Figure 4.3 Distribution of the total fatin various parts of the body of mackerel (top) and capelin (bottom) of Norwegian origin (Lohne, 1976)

The phospholipids may also be mobilized to a certain extent during sustained migrations (Love, 1970), although this lipid fraction is considered to be conserved much more than the triglycerides.

In elasmobranchs, such as sharks, a significant quantity of the lipid is stored in the liver and may consist of fats like diacyl-alkyl-glyceryl esters or squalene. Some sharks may have liver oils with a minimum of 80 % of the lipid as unsaponifiable substance, mostly in the form of squalene (Buranudeen and Richards-Rajadurai, 1986).

Fish lipids differ from mammalian lipids. The main difference is that fish lipids include up to 40% of long-chain fatty acids (14-22 carbon atoms) which are highly unsaturated. Mammalian fat will rarely contain more than two double bonds per fatty acid molecule while the depot fats of fish contain several fatty acids with five or six double bonds (Stansby and Hall, 1967).

The percentage of polyunsaturated fatty acids with four, five or six double bonds is slightly lower in the polyunsaturated fatty acids of lipids from freshwater fish (approximately 70 %) than in the corresponding lipids from marine fish (approximately 88 %), (Stansby and Hall, 1967). However, the composition of the lipids is not completely fixed but can vary with the feed intake and season.

In human nutrition fatty acids such as linoleic and linolenic acid are regarded as essential since they cannot be synthesized by the organism. In marine fish, these fatty acids constitute only around 2 % of the total lipids, which is a small percentage compared with many vegetable oils. However, fish oils contain other polyunsaturated fatty acids which are "essential" to prevent skin diseases in the same way as linoleic and arachidonic acid. As members of the linolenic acid family (first double bond in the third position, w-3 counted from the terminal methyl group), they will also have neurological benefits in growing children. One of these fatty acids, eicosapentaenoic acid (C20:5 w 3), has recently attracted considerable attention because Danish scientists have found this acid high in the diet of a group of Greenland Eskimos virtually free from arteriosclerosis. Investigations in the United Kingdom and elsewhere have documented that eicosapen-taenoic acid in the blood is an extremely potent antithrombotic factor (Simopoulos et al., 1991).

4.3 Proteins

The proteins in fish muscle tissue can be divided into the following three groups:

  1. Structural proteins (actin, myosin, tropormyosin and actomyosin), which constitute 70-80 % of the total protein content (compared with 40 % in mammals). These proteins are soluble in neutral salt solutions of fairly high ionic strength (³0.5 M).
  2. Sarcoplasmic proteins (myoalbumin, globulin and enzymes) which are soluble in neutral salt solutions of low ionic strength (<0.15 M). This fraction constitutes 25-30 % of the protein.
  3. Connective tissue proteins (collagen), which constitute approximately 3 % of the -protein in teleostei and about 10 % in elasmobranchii (compared with 17 % in mammals).

The structural proteins make up the contractile apparatus responsible for the muscle movement as explained in section 3.2. The amino-acid composition is approximately the same as for the corresponding proteins in mammaliam muscle, although the physical properties may be slightly different. The isoelectric point (pI) is around pH 4.5-5.5. At the corresponding pH values the proteins have their lowest solublity, as illustrated in Figure 4.4.

The conformational structure of fish proteins is easily changed by changing the physical environment. Figure 4.4 shows how the solubility characteristics of the myofibrillar proteins are changed after freeze-drying. Treatment with high salt concentrations or heat may lead to denaturation, after which the native protein structure has been irreversibly changed.

When the proteins are denatured under controlled conditions their properties may be utilized for technological purposes. A good example is the production of surimi-based products, in which the gel forming ability of the myofibrillar proteins is used. After salt and stabilizers are added to a washed, minced preparation of muscle proteins, and after a controlled heating and cooling procedure the proteins form a very strong gel (Suzuki, 1981).


Figure 4.4 Solubility of myofibrillar protein before and after freeze drying at pH values ranging from 2 to 12 (Spinelli et al.,1972)

The majority of the sarcoplasmic proteins are enzymes participating in the cell metabolism, such as the anaerobic energy conversion from glycogen to ATP. If the organelles within the muscle cells are broken, this protein fraction may also contain the metabolic enzymes localized inside the endoplasmatic reticulum, mitochondria and lysosomes.

The fact that the composition of the sarcoplasmic protein fraction changes when the organelles are broken was suggested as a method for differentiating fresh from frozen fish, under the assumption that the organelles were intact until freezing (Rehbein et al., 1978, Rehbein, 1979, Salfi et al., 1985). However, it was later stated that these methods should be used with great caution, as some of the enzymes are liberated from the organelles also during iced storage of fish (Rehbein, 1992).

The proteins in the sarcoplasmic fraction are excellently suited to distinguishing between different fish species, as all the different species have their characteristic band pattern when separated by the isoelectric focusing method. The method was succesfully introduced by Lundstrom (1980) and has been used by many laboratories and for many fish species. A review of the literature is given by Rehbein (1990).

The chemical and physical properties of collagen proteins are different in tissues such as skin, swim bladder and the myocommata in muscle (Mohr, 1971). In general, collagen fibrils form a delicate network structure with varying complexity in the different connective tissues in a pattern similar to that found in mammals. However, the collagen in fish is much more thermolabile and contains fewer but more labile cross-links than collagen from warm-blooded vertebrates. The hydroxyprolin content is in general lower in fish than in mammals, although a total variation between 4.7 and 10 % of the collagen has been observed (Sato et at, 1989).

Different fish species contain varying amounts of collagen in the body tissues. This has led to a theory that the distribution of collagen may reflect the swimming behaviour of the species (Yoshinaka et at, 1988). Further, the varying amounts and varying types of collagen in different fishes may also have an influence on the textural properties of fish muscle (Montero and Borderias, 1989). Borresen (1976) developed a method for isolation of the collagenous network surrounding each individual muscle cell. The structure and composition of these structures has been further characterized in cod by Almaas (1982).

The role of collagen in fish was reviewed by Sikorsky et al. (1984). An excellent, more recent review is given by Bremner (1992), in which the most recent literature of the different types of collagen found in fish is presented.

Fish proteins contain all the essential amino-acids and, like milk, eggs and mammalian meat proteins, have a very high biological value (Table 4.3).

Table 4.3 Essential amino-acids (percentage) in various proteins



















































SOURCES: Braekkan, 1976; Moustgard, 1957

Cereal grains are ususally low in lysine and/or the sulphur-containing amino-acids (methionine and cysteine), whereas fish protein is an excellent source of these aminoacids. In diets based mainly on cereals, a supplement of fish can, therefore, raise the biological value significantly.

In addition to the fish proteins already mentioned there is a renewed interest in specific protein fractions that may be recovered from by-products, particularly in the viscera. One such example is the basic protein or protamines found in the milt of the male fish. The molecular weight is usually below 10 000 kD and the pI is higher than 10. This is a result of the extreme amino-acid composition that may show as much as 65 % arginine.

The presence of the basic proteins has long been known, and it is also known that they are not present in all fish species (Kossel, 1928). The best sources are salmonids and herring, whereas ground fish like cod are not found to contain protamines.

The extreme basic character of protamines makes them interesting for several reasons. They will adhere to most other proteins less basic. Thus they have the effect of enhancing functional properties of other food proteins (Poole et al., 1987; Phillips et al., 1989). However, there is a problem in removing all lipids present in the milt from the protein preparation, as this results in an off-flavour in the concentrations to be used in foods.

Another interesting feature of the basic proteins is their ability to prevent growth of microorganisms (Braekkan and Boge, 1964; Kamal et al., 1986). This appears to be the most promising use of these basic proteins in the future.

4.4 N-containing extractives

The N-containing extractives can be defined as the water-soluble, low molecular weight, nitrogen- containing compounds of non-protein nature. This NPN-fraction (non-protein nitrogen) constitutes from 9 to 18 % of the total nitrogen in teleosts.

The major components in this fraction are: volatile bases such as ammonia and trimethylamine oxide (TMAO), creatine, free amino-acids, nucleotides and purine bases, and, in the case of cartilaginous fish, urea.

Table 4.4 lists some of the components in the NPN-fraction of various fish, poultry meat and mammalian meat.

Table 4.4 Major differences in muscle extractives

 Compound  in mg/100 wet weight1)



Shark species


Leg muscle


1) Total extractives







2) Total free amino-acids:





















Glutamic acid





















3) Creatine







4) Betaine 







5) Trimethylamine oxide 







6) Anserine 







7) Carnosine 







8) Urea 







1 It should be noted that the unit in this table refers to the total molecular weight of the compound

SOURCE: Shewan, 1974

An example of the distribution of the different compounds in the NPN-fraction in freshwater and marine fish is shown in Figure 4.5. It should be noted that the composition varies not only from species to species, but also within the species depending on size, season, muscle sample, etc.


Figure 4.5 Distribution of non-protein nitrogen in fish muscles of two marine bonyfish (A,B), an elasmobranch (C), and a freshwater fish (D) (Konosu and Yamaguchi, 1982; Suyama et al., 1977)

TMAO constitutes a characteristic and important part of the NPN-fraction in marine species and deserves further mention. This component is found in all marine fish species in quantities from 1 to 5 % of the muscle tissue (dry weight) but is virtually absent from freshwater species and from terrestrial organisms (Anderson and Fellers, 1952; Hebard et al., 1982).

One exception was recently found in a study of Nile perch and tilapia from Lake Victoria, where as much as 150-200 mg TMAO/100 g of fresh fish was found (Gram et al., 1989).

Although much work has been conducted on the origin and role of TMAO, there is still much to be clarified. Stroem et al. (1979) have shown that TMAO is formed by biosynthesis in certain zooplankton species. These organisms possess an enzyme (TMA mono-oxygenase) which oxidizes TMA to TMAO. TMA is commonly found in marine plants as are many other methylated amines (monomethylamine and dimethylamine). Plankton-eating fish may obtain their TMAO from feeding on these zooplankton (exogenous origin). Belinski (1964) and Agustsson and Stroem (1981) have shown that certain fish species are able to synthesize TMAO from TMA, but this synthesis is regarded as being of minor importance.

The TMA-oxidase system is found in the microsomes of the cells and is dependent on the presence of Nicotinamide ademine denucleotide phosphate (NADPH):

(CH3)3N + NADPH + H+ + O2 (CH3)3NO + NADP+ + H2O

It is puzzling that this mono-oxygenase can be widely found in mammals (where it is thought to function as a detoxifier), while most fish have low or no detectable actitity of this enzyme.

Japanese research (Kawabata, 1953) indicates that there is a TMAO-reducing system present in the dark muscle of certain pelagic fishes.

The amount of TMAO in the muscle tissue depends on the species, season, fishing ground, etc. In general, the highest amount is found in elasmobranchs and squid (75-250 mg N/100 g); cod have somewhat less (60-120 mg N/100 g) while flatfish and pelagic fish have the least. An extensive compilation of data is given by Hebard et al. (1982). According to Tokunaga (1970), pelagic fish (sardines, tuna, mackerel) have their highest concentration of TMAO in the dark muscle while demersal, white-fleshed fish have a much higher content in the white muscle.

In elasmobranchs, TMAO seems to play a role in osmoregulation, and it has been shown that a transfer of small rays to a mixture of fresh and sea water (1: 1) will result in a 50 % reduction of intracellular TMAO. The role of TMAO in teleosts is more uncertain.

Several hypotheses for the role of TMAO have been proposed:

According to Stroem (1984), it is now generally believed that TMAO has an osmoregulatory role.

As the occurrence of TMAO had previously been found virtually only in marine species until the observation published by Gram et al. (1989), it was speculated that TMAO together with high amounts of taurine could have additional effects, at least in fresh water fish (Anthoni et al., 1990 a).

Quantitatively, the main component of the NPN-fraction is creatine. In resting fish, most of the creatine is phosphorylated and supplies energy for muscular contraction.

The NPN-fraction also contains a fair amount of free amino-acids. These constitute 630 mg/ 100 g light muscle in mackerel (Scomber scombrus), 350-420 mg/ 100 g in herring (Clupea harengus) and 310-370 mg/100 g in capelin (Mallotus villosus). The relative importance of the different amino- acids varies with species. Taurine, alanine, glycine and imidazole-containing amino-acids seem to dominate in most fish. Of the imidazole-containing amino-acids, histidine has attracted much attention because it can be decarboxylated microbiologically to histamine. Active, dark-fleshed species such as tuna and mackerel have a high content of histidine.

The amount of nucleotides and nucleotide fragments in dead fish depends on the state of the fish and is discussed in section 5.

4.5 Vitamins and minerals

The amount of vitamins and minerals is species-specific and can furthermore vary with season. In general, fish meat is a good source of the B vitamins and, in the case of fatty species, also of the A and D vitamins. Some freshwater species such as carp have high thiaminase actitity so the thiamine content in these species is usually low. As for minerals, fish meat is regarded as a valuable source of calcium and phosphorus in particular but also of iron, copper and selenium. Saltwater fish have a high content of iodine. In Tables 4.5 and 4.6 some of the vitamin and mineral contents are listed. Because of the natural variation of these constituents, it is impossible to give accurate figures.

Table 4.5 Vitamins in fish


A (IU/g)

D (IU/g)

B1(thiamine) (µ/g)

B2 (riboflavin) (µ/g)

Niacin (µ/g)

Pantothenic acid (µ/g)

B6 (µ/g)

Cod fillet 








Herring fillet








Cod-liver oil




1) 3.4

1) 15

1) 4.3


1) Whole liver

SOURCE: Murray and Burt, 1969

Table 4.6 Some mineral constituents of fish muscle

Element Average value (mg/100 g) Range (mg/100 g)
Sodium 72 30 -134
Potassium 278  19 -502
Calcium 79 19 -881
Magnesium 38 4.5-452
Phosphorus 190 68-550

SOURCE: Murray and Burt, 1969

The vitamin content is comparable to that of mammals except in the case of the A and D vitamins which are found in large amounts in the meat of fatty species and in abundance in the liver of species such as cod and halibut. It should be noted that the sodium content of fish meat is relatively low which makes it suitable for low-sodium diets.

In aquacultured fish, the contents of vitamins and minerals are considered to reflect the composition of the corresponding components in the fish feed, although the observed data should be interpreted with great caution (Maage et al., 1991). In order to protect the n-3 polyunsaturated fatty acids, considered of great importance both for fish and human health, vitamin E may be added to the fish feed as an antioxidant. It has been shown that the resulting level of vitamin E in the fish tissue corresponds to the concentration in the feed (Waagbo et al., 1991).