CHAPTER VI. 



THE RATE OF GROWTH OF FOOD-FISHES. 



The importance of this subject from an economic point of 

 view would be difficult to exaggerate, and at the same time it 

 is remarkable how very little is definitely known in connection 

 with it. 



It has already been pointed out in the Introduction that 

 the various changes undergone by a fish in its transition from 

 the egg to the adult condition fall under two heads, — firstly, 

 quantitative changes, which involve increase in bulk, and 

 secondly, qualitative changes, or those which are concerned 

 with the differentiation of organs. 



It is well to understand clearly that these two series of 

 changes have not necessarily any direct connection, although 

 the quantitative changes of growth appear to precede to a 

 great extent those of development or differentiation. 



These quantitative changes which cause the phenomena 

 of growth are held by most zoologists to be either the direct 

 effect of, or intimately connected with, cell-division. Thus if 

 cell-divisioa takes place at a more rapid rate than the loss of 

 cellular tissue to which the organism is constantly subjected, 

 the result is an increase in the number of cells and of general 

 bulk, or, in other words, growth, and so far as is known there 

 is no inherent reason why this growth should not proceed 

 throughout the life of the organism. We do not mean by 

 this that there is no limit whatever to the size attainable 

 by any given species; thus, to quote Weismann, "although 

 many fishes, reptiles and lower animals are said to grow during 



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