FISHERY INDUSTRIES OF THE UNITED STATES, 1935 91 



from July to January 1, 1936. The two remaining samples contained 

 14 percent and 25 percent fat. 



Although not consistent, the data indicate that halibut livers in- 

 crease in fat content from summer to mid-fall and then decrease to 

 the close of the season in November or December. Preliminary data 

 on samples of oil tested in the laboratory indicate variation in certain 

 chemical constants and vitamin A values ranging through wide 

 limits. A more complete study is being made. 



EXTRACTION OF OIL FROM HALIBUT LIVERS 



Halibut livers do not give up oil by simple heat treatment, as do 

 the livers of cod and related fish. For this reason, solvent extraction 

 was used in the first stages of the industry's development. During 

 the past 3 or 4 years, the several manufacturers of halibut-liver oil 

 have developed effective methods of oil extraction without recourse 

 to solvents, with a resultant improvement in the quality and appear- 

 ance of the oil. 



In order that the oils referred to in the preceding section would be 

 representative of the grade of oil entering commerce at the present 

 time our technologists were required to give considerable attention 

 to methods of extraction. Most effective and rapid results were 

 obtained by first disintegrating the livers mechanically without emul- 

 sification, autoclaving for a short time in an acid medium to break 

 down further the liver tissue, making the solution slightly alkaline, 

 and reheating for a short period and centrifuging. 



The livers were found to vary considerably in physical condition 

 and consequently with ease of extraction. For this reason further 

 discussion of the experimental procedures used and their efficacy will 

 be reserved for our regular report series where they can be discussed 

 in detail at the completion of the investigation. 



VARIATION IN THE FAT CONTENT OF HALIBUT 



On several occasions during the past year the bellies of halibut 

 held for storage were observed to become bluish and more or less 

 mottled in appearance when frozen. Such fish were considered 

 unmarketable by the trade since the bellies of frozen halibut are 

 expected to be unblemished white in color. 



Specimens of such fish were submitted for the attention of the 

 technologists in our Seattle laboratory, and it was found that the 

 discolored appearance was due to the belly skin becoming more or 

 less transparent when the fish were frozen. This resulted in the flesh 

 immediately beneath the skin showing through. Upon further exam- 

 ination and laboratory tests the fish were found to be particidarly 

 lean with practically no fat storage adjacent to the belly skin as is 

 the case in a normal fish. 



Since this extreme variation in fat content had resulted in market- 

 ing losses and has possible relation to the biological work of the 

 International Fisheries Commission in the study and regulation of 

 the halibut fishery, our Seattle technological laboratory began an 

 investigation of this problem in cooperation with the commission. 

 Periodic samples of small, medium, and large halibut have been 

 taken at intervals throughout the season, from the various halibut 



