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Fish and fishery products contain water, proteins and other nitrogenous compounds, lipids, carbohydrates, minerals and vitamins. Their chemical composition varies greatly from one species and one individual fish depending on age, sex, environment and season.

The variation is also closely related to feed intake, migratory swimming and sexual changes in connection with spawning. Fish have starvation periods for natural or physiological reasons (such as migration and spawning) or because of external factors such as shortage of food. Spawning, whether occurring after long migrations or not, usually requires higher levels of energy. In fact, fish with energy depots in the form of lipids rely on this. Species migrating long distances before reaching specific spawning grounds or rivers may use proteins in addition to lipids for energy, depleting both lipid and protein reserves and generally reducing their biological condition. In addition, most species do usually not ingest much food during spawning migration and are therefore not able to supply energy through feeding.

The table below shows the principle components of fish as well as their variation. The average composition of beef muscle has been included for comparison.

Principle constituents of fish and beef muscle (in percentage)
Constituent Fish fillet Beef muscle

Minimum

Normal variation

Maximum

Protein

6 16-21 28 20

Lipid

0.1 0.2-25 67 3

Carbohydrates

 

<0.5

 

1

Ash

0.4 1.2-1.5 105 1

Water

28 66-81 96 75

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

 
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