STORAGE OF FAT IN MUSCULAR TISSUE OF KING SALMON. Si 



It is out of the question to assume that a Monterey fish destined to migrate as far 

 north as the mouth of the Columbia River is in the condition that will exist at the time 

 of arrival. Such a salmon is in the growing stage. It will certainly increase in size in 

 so long a feeding journey and probably will also somewhat increase its fat content. 



The Monterey fish are the only ocean-feeding fish available as examples of mature 

 specimens typical of the vSacramento and to a certain extent of the Columbia Basins. 

 It follows, therefore, that one must use these specimens as best he can for the purpose. 

 The matter resolves itself, somewhat, into a question of the ability of the investigator 

 to select and judge the type that most nearly approaches the mature one." There is a 

 wide extreme of maturity represented among the Monterey fish. The small fish give 

 all evidences of being relatively young and growing specimens. The larger fish are proven 

 to be the older ones by the work of Gilbert, who finds a close correlation between size 

 and age.* His determinations indicate that these larger fish have been feeding in the 

 ocean for four, five, or even more years, according to the size of the specimen chosen. 

 It seems reasonable to assume that such fish will not undergo any very great change 

 in the average fat content during the interv^ening months between the time of the Mon- 

 terey feeding and the beginning of the spawning migration. The larger Monterey fish 

 may be taken as the best available examples typical of the disposal of the tissue fat in 

 the late stages of the feeding cycle. On this ground observations and protocols are 

 presented on Monterey specimens. 



In the chapter on the types of salmon muscular tissue as regards the storage of fat 

 the muscle characteristics are given in sufficient length to enable one to use them in 

 presenting the picture of the fats and fat variations. It remains now to give the 

 detailed picture of the normal fat content of salmon muscle at the time when the feed- 

 ing ceases. Under this category will be presented the following muscle types: 



Normal fat content of the trunk pink 7nnsclc. — The pink muscle, which represents 

 the greater proportion of the total mass of muscle of the salmon, contains an enormous 

 total load of fat at the time the salmon cease feeding. Estimating on the basis of various 

 chemical studies made in other connections, I would say that this fat loading varies 

 between 15 and 25 per cent. This great variation represents the normal variation in 

 fat content. 



The fats of the pink muscle are distributed in the connective tissue between the 

 muscle fibers — i. e., they are intermuscular. The pink muscle carries a relatively large 

 amount of connective tissue which supports the muscle fibers and the blood vessels, 

 and this connective tissue has a high percentage of adipose tissue. In it are found enor- 

 mous numbers of fat droplets, which vary within a wide range of size. The smallest 

 droplets are often not more than i or 2 /< in diameter, but there are numerous fat globules 

 of this region that are as much as ioo/( in diameter. No figure is presented of this normal 

 material, but figure 8, plate vi, drawn from an Ilwaco specimen (no. 118), represents 

 very well the average appearance of the intermuscular fat of the normal tissue. 



a The alternative is to figure back from the tirst available stage in the spawning migration. For the Columbia River this 

 latter method I believe gives a truer picture of the normal condition. Attention will be called to this fact in the discussion of 

 Ilwaco types. 



^ Prof. Chas. H. Gilbert, who is making extensive studies on the salmon migration and the salmon age, observes that there 

 is. within certain limits, a close correspondence between size and age. It follows that the larger fish have a longer ocean-feeding 

 period, a fact for which we have heretofore had no conclusive proof. Also it is evident that salmon mature sexually at greatly 

 varying ages. (Gilbert, C. H.: Age at maturity of the Pacific coast salmon of the genus Oncorhynchus, Bulletin of the 

 U. S. Bureau of Fisheries, Vol. xxxn, 1912, p. i.) 



