Fish silage is a liquid product made from whole fish or parts of fish that are liquefied by the action of enzymes in the fish in the presence of an added acid. The enzymes break down fish proteins into smaller soluble units, and the acid helps to speed up their activity while preventing bacterial spoilage. Silage made from white fish offal that does not contain much oil, but when it is made from fatty fish like herring it may be necessary to remove the oil at some stage.
The composition of fish silage is very similar to that of the material from which it is made. A typical analysis of white fish offal is:
· 80 per cent water,
· 15 per cent protein,
· 4.5 per cent ash
· 0.5 per cent fat,
and the composition of silage from offal is virtually the same.
Whole fatty fish like sprats and sand eels have a higher protein and fat content, and correspondingly lower water and ash content.
Production of fish silage is a viable alternative to fish meal, especially in location where small amount of fishery waste or by-catch is produced It has been shown that by-catch or fish wastes, whole, chopped or ground, preserved in molasses or as fermented or acid silage, in the form of a paste or block, can replace more conventional sources of protein for pigs, ducks, sheep, cows, beef cattle and even camels!
While the technology for the preparation offish silage exists. Its commercial application will depend on extension to producers and on its opportunity cost versus that of other conventional protein sources, as well as on the existence of other means of processing to meet environmental regulations. At the moment it is not commericially available on a widescale.