BUREAU OF FISHEEIES XXV 



quantity and an increase of 4 per cent in value compared -with the 

 production and its value in 1922. The pearl-button industry, cen- 

 tering in Iowa, manufactured pearl buttons and various novelties 

 from fresh-water mussel shells, to a value of $6,144,515 in 1929. The 

 fisheries of Lakes Pepin and Keokuk show decreased yield in 1929 

 compared Avith that in 1928. 



TECHNOLOGICAL INVESTIGATIONS 



The division's technologists have been conducting research mainly 

 on problems relating to the manufacture of fish meal and oil, the 

 feeding value of marine products, the handhng and transportation 

 of fresh and frozen fish, and the preservation of nets. 



NET PRESERVATION 



In the study of trap-net preservation, selected new treatments 

 have been tested on trap-net and gill-net threads in many fishing 

 waters throughout the country. As a result certain essential prin- 

 ciples of preservation applicable to all localities have been established. 



Technical development of gill-net preservatives has followed 

 scientific study. Several fishermen have used gill nets treated with 

 browTi or green colored preservatives with results comparable to the 

 fishing power of white nets. 



BY-PRODUCTS 



Menhaden. — The bureau's technical study of the menhaden in- 

 dustry included the determination and evaluation of the losses of 

 material encountered in the reduction process and studies of methods 

 appUcable to the present process whereby such losses coidd be re- 

 duced. The various recoverA" methods studied indicate that either 

 all or a considerable portion of press-liquor losses may be recovered 

 at a profit. The same is true of the oil now lost. Studies on methods 

 of drying press cake show that present dryer losses may be reduced 

 over one-half by drying in a high-capacity steam dryer, and the re- 

 sultant dried material is of better quahty and has a greater nutri- 

 tional value. Studies also indicate that a considerable reduction in 

 the cost of raw material would result from proper storage conditions 

 aboard vessel. 



Reduction of vjaste jrom nonoily fish. — Studies on the reduction of 

 this type of material show that it may be reduced in one operation 

 with some success if dried under reduced pressure. Most desirable 

 results were obtained by reducing the size of the initial charge and 

 having scraping blades on the agitator come in direct contact with 

 the dry^er walls. 



Waste fi.<ih and sharks. — Studies on the utilization of waste fish and 

 sharks in amounts too small to warrant investment in mechanical 

 reduction equipment, show that such material may be reduced from 

 the raw state by acidulation and solar drying. By this simple pro- 

 cedure, many fishermen without any considerable effort or expense can 

 realize a profit from material that is now little more than a nuisance. 



NUTRITIVE VALUE OF FISHEKV PRODUCTS 



Research in the nutritive value of fishery products has consisted of 

 the following: (1) A joint stud}^ by this bureau and the Bureau of 

 Chemistry and Soils of the Department of Agriculture of the vitamin 



