486 MARINE PRODUCTS OF COMMERCE 



Liquid Fish 



Some fish waste is converted into a wet or semiliquid protein supplement for 

 use in animal and poultry feed. The waste material used in the preparation of this 

 liquid protein or "liquid fish" consists of the inedible remains after fillets are 

 cut. The most generally used species of fish are those ordinarily known as non- 

 fatty fish: cod, haddock, pollock, redfish, etc. The bodies of these species contain 

 slightly more than 1 per cent oil, and are not valuable as a source of fish body 

 oil. Some whole fish which have no value as food are often sold for reduction 

 purposes. 



This process is in the early stage of development; even though a firm may be 

 preparing and marketing the liquid fish, many problems remain to be solved. At 

 present it is impossible to obtain technical details as to manipulation. The waste 

 material is chopped into small pieces; these are placed in some form of digestion 

 apparatus where the fish flesh is hydrolyzed to produce the constituent amino acids 

 which compose the complete protein. 



One method for accomplishing hydrolysis or partial digestion is by adding acid 

 and heating the mass at a temperature of approximately 150° F (66° C). The 

 naturally occurring enzymes of the fish flesh and viscera are activated by the 

 acid and increased temperature and result in a partially digested hquid protein. 

 The time varies according to the particular material under treatment. The acid 

 mixture should be agitated during the heating period to insure uniform reaction 

 throughout the mass. 



When hydrolysis is completed, it is necessary to condense the material to about 

 50 per cent solids. This is done by evaporating some of the excess water content 

 either at atmospheric pressure or under reduced pressure. A lower temperature 

 is required for reduced pressure consequently there is no danger of scorching 

 the finished product. After this reaction is completed and the water removed, 

 a slight quantity of acid remains and acts as a preservative. The "liquid fish" is 

 shipped in tank cars to the feed mixers, where it is included in a dry mixed feed. 



