Basically the manufacture of fish silage is a means of preserving 'trash' fish, waste fish heads and viscera, prawn waste, etc. The waste marine material is ground and mixed with sulphuric, hydrochloric or, preferably, propionic or formic acid (alone or in mixtures) to cause liquifaction and to prevent bacterial decomposition. The product of this process is sometimes known as acid silage. An alternative technique consists of introducing lactic acid producing organisms into a ground fish-carbohydrate mixture. The result is sometimes referred to as biological fish silage and the process as lactic acid fermentation. The lactic acid bacteria produce the acid necessary to preserve the fish in the latter alternative. The protein splitting enzymes (proteolytic enzymes) of the fish, under the acid conditions produced, cause the product to become more liquid. The resulting product may be stored as a liquid or mixed with various dry materials to form a material which can be used directly as a fish feed or used as an ingredient in a compound feed. Fish silage has been used with some success in fish feeding but has not yet found favour as a shrimp feed. There is no fundamental reason why it should not be a good ingredient for shrimp feeds, however.
There are many different ways of preparing fish silage (see 'further reading' below).
Further reading for Appendix VI:
Disney et al., 1978, Disney and James, 1980, Stanton and Yeoh, 1977.