506 



V. H. BUREAU OF FISHEBIES 



presented in this chapter. In the first place, the main fiiiGtuations 

 in the composition of fish flesh are in the percentage of moisture and 

 the percentage of fat. The percentage of protein does not fluctuate 

 widely. The other consideration to be borne in mind is that there 

 is very slight variation in the percentage of ash or inorganic matter 

 in the different types of fish. This might appear surprising at first 

 glance, but it is not. Just as the protein or cell substance does not 

 vary much in composition, neither does the amount of inorganic 

 matter associated with it. As already pointed out, a certain minimum 

 amount of inorganic matter of certain types must be present for the 

 normal life of the cells of the body, which select from the food ma- 

 terials offered to them those inorganic constituents which they need 

 for their growth and functioning. The rest is eliminated, as inorganic 

 substances are not stored in the body to any great extent. 



There is one difficulty in drawing general conclusions from At- 

 water's analyses as to the average composition of the various types 

 of fish. It is this. Professor Atwater usually analyzed but one or 

 two samples of the different species of fish, and it became apparent 

 to other investigators in the years that passed after this pioneer work 

 had been done that there was a great variation in the composition of 

 the same kind of food fishes, due to several factors. In the first 

 place, individual fish of the same school caught at the same time 

 often differ widely in composition. This is not due to different stages 

 of development, age, or sex, but must be ascribed to what is called 

 '^individual variation," or, more likely, to the greater success of some 

 fish in securing their food in the struggle for existence. Then, there 

 is another factor, namely, the proximitj^ to the time of spawning. 

 This is a very important factor and one which will be shown quite 

 clearly in the tables to appear later on. Third, there is considerable 

 evidence that the locality where fish are caught may cause its own 

 type of variation in composition. Whether such variation, apparently 

 due to locality, is caused primarily by differences in food supply or to 

 some more fundamental consideration we do not know as yet. 



Table 3. — Variation in composition of some important food fishes analyzed at 

 different seasons of the year 



[Analyses of the edible portion on the fresh basis] 



