224 U. S&. BUREAU OF FISHERIES 
Refractive index of free oil in canned salmon 





Refractive index 
Species eae Sate a Tae 
samples Range Mean pee 
; 1936 109 | 1.4693-1.4743 | 1.47159} 0, 00101 
ChInCOK Ona ean a eee ae { i938 77 | 1.4698-1.4753 | 1.47178 00109 
1936 275 | 1.4705-1.4768 | 1. 47328 00104 
T6001, BOUKDY 0 2221s 3 eee a { 1038 225 | 1.4710-1.4773 | 1.47475 00116 
1936 104 | 1,4720-1.4766 | 1.47444 00090 
Chum or keta-.------------------------- { 1938 103 | 1.4734-1.4771 1. 47489 00068 
1936 125 | 1.4718-1.4787 | 1.47584 00089 
By erat Ot aaa art ceeEeeTe { 1938 113 | 1.4744-1.4788 | 1.47665 00074 
1936 186 | 1.4707-1.4789 | 1.47634 00126 
Bot a SRS oncaceanssan scones: { 1938 152 | 1.4750-1.4796 | 1.47718 00101 


CHANGES IN THE COMPOSITION OF PINK SALMON (Oncorhynchus gorbuscha) 
The commercial fishery for salmon is predicated upon the natural 
instinct of these fish to return to their parent streams to spawn and 
die. During the course of the spawning migration, the fish undergo 
considerable physical change and have been assumed to become poorer 
in quality, inasmuch as there is a gradual decrease in the pigmentation 
and firmness of the flesh and a definite diminution of the fat content 
of the edible portion of the carcass. 
In last year’s report reference was made to chemical analyses of the 
flesh of pink salmon which indicated that, from a chemical standpoint, 
the pronounced changes in physical appearance were accompanied by 
much less change in the nature and composition of the flesh protein. 
During the past year feeding tests were made with extracted pink 
salmon flesh which substantiate the chemical tests in that there ap- 
peared to be no significant difference in the nutritive value of the 
extracted flesh of early- and late-caught fish despite the marked 
difference in physical appearance. A final report incorporating and 
discussing the various chemical and biological data is nearing comple- 
tion and will be submitted for publication shortly. 
PEROXIDE TEST AS A MEASURE OF OXIDATIVE DETERIORATION OF FISH OIL 
Several years ago a study was begun on the development of ran- 
cidity in the oil of fatty fish held under varying conditions of storage. 
The criterion of rancidity had been the Wheeler test for peroxide 
formation. Further investigations of this general nature were planned 
but it was thought advisable to make a preliminary study of the 
various tests of rancidity, as to the type of rancidity each test indi- 
cated, and the relation of the various tests to each other and to 
that ultimate criterion of rancidity—the organoleptic test which, 
unfortunately, is not easily capable of quantitative determination. 
A study of four methods for testing rancidity was begun, therefore, 
during the past year. Measurement of oxygen absorption as an esti- 
mation of the degree of rancidity was tried and discarded as impracti- 
cable. TheShibsted test for fat aldehyde was then applied to a number 
of fresh oils. Wheeler peroxide values on the same oils showed no 
correlation whatever to the Shibsted values. A group of measured 

Pa 
