Post-mortem change, fish

The other enzymatic reactions found in fish seem to be common to all vertebrates. Study of these reactions has been mainly directed towards the biochemical changes occurring post-mortem in fish muscle, the so-called internal factors of fish spoilage which have involved investigations in glycolysis, lipolysis, and proteolysis. 

Tarr, H.L.A. (1966) Post-mortem changes in glycogen, nucleotides, sugar phosphates and sugars in fish muscles. A review. J. Food Sci. 31, 846-854. 

Trimethylamine oxide, (CH3)jN+0, an onium salt found in marine but never in fresh-water fishes. Rich sources are eephalo-pods and crustaceans, the muscle of the lobster containing about 0 3 per cent. The oxide is soluble, non-toxic and almost neutral, and is an important excretory form of nitrogen. Among the elasmobranchs it serves in the maintenance of fluid equilibrium, and is responsible for 20-25 per cent, of the total osmotic pressure of the blood. It is rapidly decomposed by post-mortem autolytic and bacterial changes, and the liberated trimethylamine, (CH3)jN, characterises the odour and taste of stale marine fish. 

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