176 Investigations on the Life-History of the Salmon in Fresh Water. 



showing that the fish is again becoming capable of taking and using 

 food. 



IX. Food Value of Salmon. 



The food value per unit of weight of muscle deteriorates as the season 

 advances. In each fish caught in the estuaries the food value remains 

 almost constant, the larger size of the late-coming fish making up for 

 the deterioration of the flesh. The food value of each fish caught in the 

 upper waters is less than of those caught in the estuaries, and in 

 October and November is only about one-third that of fish caught in 

 the river- mouth. 



This series of observations is only a contribution to a very large and 

 very interesting subject. Many points yet remain to be investigated, 

 while others touched upon here require extension and confirmation. As 

 regards the course of migration, our investigations cover only a few 

 months of the year, and interesting results are to be expected by 

 extending the investigations into the other seasons. 



We have given evidence to show that the early-coming fish occupy 

 the upper reaches of the river, but a more extended series of investiga- 

 tions is required to show whether the late-coming fish, which during 

 October and November are found in the lower waters, really spawn 

 there, or whether they ultimately pass up to the upper waters. 



Whether the rate of migration can be satisfactorily investigated in 

 our short Scottish rivers is very doubtful. In the great Canadian 

 rivers, such as the Fraser, very valuable results might be expected from 

 the study of this question. Indeed it would be a matter of the greatest 

 importance to have the observations recorded in these papers checked 

 and extended on a large scale in such a river, with its unbounded supply 

 of fish and hundreds of miles of water way. 



The downward migration of kelts requires further study. Of the 22 

 kelts received in April, 1897, all were females. Is this a mere conci- 

 dence, or do the male kelts descend at a different time from the female ? 

 Some of the more important changes in the female kelts have been 

 dealt with, but the interesting question of the loss of the great maxillary 

 development in the male is yet to be elucidated. 



The study of these and many other problems must be left for future 

 investigations. 



GLASGOW : 



PRINTED BY JAMES HEDDERWICK & SONS, 

 FOR HER MAJESTY'S STATIONERY OFFICE. 



