234 FISH HMCHERY MANAGEMENT 



FORMULATED FEEDS 



Formulated feeds are a mixture of ingredients processed into pellets, 

 granules, or meals and may be either supplemental or complete rations. 



Supplemental feeds are formulated to contain adequate protein and en- 

 ergy, but may be deficient in vitamins and minerals which the fish are ex- 

 pected to obtain from natural foods. Such feeds are fed to catfish and other 

 fish reared at low densities in ponds. 



Complete feeds are formulated to provide all essential vitamins and nu- 

 trients required by fish and are designed to provide optimal growth. If high 

 densities of fish are being reared, a complete feed must be provided, as na- 

 tural feeds will be limited or absent. Such feeds must be of a physical con- 

 sistency that will allow them to be fed in the water without breaking down, 

 but still be easily ingested and digested by the fish. Properly sized feeds 

 are required for different sizes of fish because fish normally do not chew 

 their food. The feed must be palatable to the fish so that it will be readily 

 consumed and not left to dissipate into the water. Dust and fine particles 

 that may occur in the large-sized feeds will create problems because they 

 are not efficiently consumed and, if present in excess, cause water pollution 

 and gill disease. 



Feed Manufacturing 



Formulated feeds are manufactured in the forms of meals, granules, 

 compressed pellets (sinking), expanded pellets (floating), and semimoist 

 pellets. The use of dry pelleted feeds provides several advantages over oth- 

 er feeding programs. Such feeds are available at all times of the year in any 

 quantity. Fish producers can select the size of feed satisfactory for feeding 

 fish through the rearing cycle. Pelleted feeds give lower feed conversions 

 and lower feed cost per unit of weight gain than natural or wet feeds and 

 cause less waste and contamination of the rearing water. No hatchery labor 

 is required to prepare the feed. Pelleted feeds purchased in bulk provide 

 additional efficiency in lower costs of handling and storage. The conven- 

 ience of using automatic feeding equipment is also possible with bulk 

 feeds. 



Compressed or sinking pellets are made by adding steam to the feed as it 

 goes into the pellet mill. The steam increases the moisture content by 5 to 

 6% and raises the temperature to 150-I80°F during processing. The mix- 

 ture is forced through a die to extrude a compressed, dense pellet. The pel- 

 lets are air- dried and cooled immediately after pelleting. The moisture con- 

 tent of pellets must be sufficiently low (less than 10%) to prevent mold 

 growth during storage. 



