THE RATE OF GROWTH OF FOOD-FISHES. 107 



degree of accuracy but one or two extreme cases may con- 

 siderably upset the results. 



A comparison of the curves derived by this method with the 

 table of maxima and minima of sexual maturity given in this 

 chapter shows that the majority of the food-fishes attain sexual 

 maturity for the first time during their third year, and in the 

 case of the males it is very likely that most come to maturity 

 during their second year. As in other remarks concerning fishes 

 in this department we must be understood to refer only to the 

 average, and indeed it is likely that the average attainment of 

 maturity may be as late as the third and fourth years for males 

 and females respectively. 



Further we may notice that the larger species of fishes 

 appear to differ from the smaller in their size mainly on 

 account of a greater rate of growth from the outset, by which 

 is meant, from the hatching epoch, although the size of the egg 

 and newly hatched larva only corresponds in a very rough way 

 to that of the adult. Thus the ling shows a more rapid rate of 

 growth during the whole period of maturity than the gurnard 

 or smaller species, and the same applies to the plaice amongst 

 flat fishes compared to the dab and others. 



We have, up till now, left out of consideration all points in 

 connection with differentiation of organs. This development, 

 proceeding contemporaneously with growth, reaches a culmi- 

 nating point in the maturation of the sexual organs. These 

 are the last organs of the body to become functional, and a fish 

 which has reached this stage may be known as ' mature ' or 

 ' sexually mature,' while one which has not yet become sexually 

 functional is 'immature.' Some observers have attempted to 

 apply these terms as if they were synonymous with 'fully- 

 grown,' but from what has been said above, the latter term is 

 meaningless and even misleading as applied, at any rate, to the 

 vast majority of fishes. If we wish to speak of young and 

 adult fishes we can only do so by selecting an anatomical or 

 physiological feature as a line of demarcation between the two, 

 and the feature which is eminently suitable for this purpose is 

 that of functional sexuality. The terms ' immature,' ' mature,' 

 ' young ' and ' adult ' can not be scientifically defined in any 



