ON TROUT. 



59 



It will be noticed that there are no mature fish among any of the 

 individuals which are only two or three winters old, and that males and 

 females occur in about equal numbers. It is only in the older groups, 

 from four winters upwards, that we meet with maturity, and these mature 

 fish are, without exception, males. The older females have migrated. 

 Thus we meet here with conditions quite analogous to those we found in the 

 case of salmon parr so far as maturity and sex are concerned. The table 

 shows us also that this river does not contain any other trout than sea 

 trout, since no stock could last which depended solely on spawning males. 

 If fresh water trout or stationary trout existed side by side with the sea 

 trout we should be sure of the fact by a relatively plentiful occurrence of 

 mature females. 



The fish in the Dalos river, therefore, which have not been to the sea, 

 are merely the young progeny which have not yet migrated, and of which 

 only the oldest males are mature, and the supplement of the stock is to be 

 found by examining the fish, which have evidently been in the sea, and 

 which are given in Table XIX. 



By means of this table we can draw up the following statement of sex 

 and sexual characteristics, in relation to the number of winters which the 

 fish had completed after migration. 



This shows us in the first place that the number of males and females 

 in the corresponding stages of existence is fairly equally balanced. Here, 

 too, the males are the first to begin spawning, as some of them spawn after 

 merely one summer in the sea. After a stay of one winter and more in 

 the sea the proportion of both males and females which spawn is 

 increasingly augmented, though in each age-class there are still some 

 that do not participate. It is not until we reach the oldest stages that we 

 find that all the fish enter the river to spawn. 



In Table XX., I have endeavoured to illustrate this state of affairs 



