STORAGE OF FAT IN MUSCULAR TISSUE OF KING SALMON. I I i 



The intramuscular fat is arranged practically the same as in the trunk muscle, except that the 

 size of the droplets is smaller tliroughout. Droplets 2 /i in diameter are relatively rare and the liposomes 

 in the chains in the middle portion of the fibers run about 0.5 to o.S /i in diameter, about the size of 

 the liposomes in the relatively fat-free fibers of the trunk. 



The teased fibers give an explanation of the diffuse appearance of the stain in this section 

 (M58-5g). It is due to the extremely small but numerous liposomes. Liposomes are also present in 

 groups just under the sarcolemma in many places. In the largest chains observed in fibers that seem 

 relatively better supplied with fat the liposomes measure from i to 1.2 u in diameter. 



FAT I.N THE TISSUES OF SALMON FROM THE SPAWNING GROUNDS. 



SaliBon at the spawning grounds in the Clackamas River, at Cazadero, Oreg., 

 have been fasting from three to four months. During the entire time there is no food 

 source for the energy which the salmon have expended other than in the tissues and in 

 the stores of fat. One would certainly expect the great fat storehouse to be sharply 

 drawn on if not exhausted by the time this stage of the life cvcle is reached. 



We have taken fish from the spawning grounds so emaciated and so weakened 

 that they were scarcely able to maintain equilibrium in the river currents. One knows 

 that some of these fish would die in a day or so even if they were kept in the water in 

 the most carefully protected condition." Fat is still present in the muscular tissues 

 of such salmon. Its percentage is low, yet the microscope reveals an unexpected 

 quantity. 



There is considerable variation among the different individuals present at Cazadero. 

 All of the early September spawners are undoubtedly of the so-called spring run of salmon. 

 They have been in the river at least since May or June (estimated). Yet there are 

 specimens that have very much more fat than the dying salmon mentioned above. 

 These variations are shown best in a comparative study of the various types of muscle. 



Trunk pink muscle. — The preparations of pink muscle show a sharp contrast with 

 the loading of fat observed in the nonnal fish and in fish from the mouth of the Columbia 

 River. Instead of the large intermuscular fat globules there are only small droplets 

 present and these are few in number. They are located in the angles in the larger 

 connective tissue masses which mark the points where several fibers are grouped. If 

 two fibers are compactly pressed to each other there are no fat droplets between them. 

 Where several fibers are separated by masses of connective tissue there may still be 

 small groups of fat droplets. In such cases the fat droplets are small in size and few in 

 number. In one specimen, no. 131, the number of intermuscular fat droplets averages 

 about one droplet to ten fibers, and the largest droplet present measures only 6 /( in 

 diameter. This quantity of intermuscular fat is insignificant. 



The presence of a significant amount of intramuscular fat in these most exhausted 

 specimens from the spawning grounds is in striking contrast to the disappearance of 

 the intermuscular fat. The intramuscular fat is in minute liposomes less than 0.5 ft 

 in diameter. The largest liposomes are in the smallest fibers. They are scattered 

 throughout the substance of the fibers except in the surface band of fibrillse, where the 

 absence of interfibrillar fat gives the appearance of a clear band of fibrils around the 

 superficial border of the muscle fiber as seen in transverse section. Around the sur- 

 face of the pink fibers and under the sarcolemma are groups of fat droplets. Where 



o Males were selected from those retained in the spawning pens. In one instance salmon for study were selected from those 

 most advanced in retrogression yet with no obvious fatal lesions. Of those not used three had died by the next morning. This 

 is positive evidence that the salmon selected were at the dying stage. 



