Chemical elements of fish
Water, lipid and protein content in various fish species vary greatly, as outlined in the table below.
The lipid fraction is the component with the greatest variation. Often, the fluctuations within a fish species will display a characteristic seasonal curve with a minimum around the time of spawning.
Although the protein fraction is rather constant in most species, changes have been observed, such as the protein reduction occurring in salmon during long spawning migrations and in Baltic cod during the spawning season.
The carbohydrate content in fish muscle is very low, usually below 0.5 percent. 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 freed ribose after post mortem autolytic changes.
Aquacultured fish can also vary in composition, although more predictably because several factors are controlled. In fact, a fish farmer is able to design, to some extent, the composition of the fish by selecting the farming conditions - the feed composition being the single most pronounced factor to have an impact on the composition of the cultured fish.