PROPAGATION AND PROTECTION OP THE RHINE SALMON. 



823 



SO far from being mature that until lately they have been considered as quite 

 sterile animals. It has been shown, however, by the investigations of Miescher- 

 Ruesch and myself, that these salmon are by no means sterile, but only immature 

 fish and that they will develop their sexual organs in the course of the year and 

 during their residence in the fresh water. Some are males and some females, the 

 latter, however, being in the majority. They are not very numerous in the 

 winter months, but gradually their number increases ; they are very fat and of the 

 highest value as human food. They continue to ascend in spring, are most 

 numerous from March to May, and go on ascending until the spawning time. 

 From the beginning of their ascent until 

 far up in spring they are called " winter 

 salmon;" they are the same salmon, 

 however, as those which from April or 

 May until the spawning time in Novem- 

 ber and December are called " large sum- 

 mer salmon." Their sexual organs, 

 which are in quite an undeveloped con- 

 dition in November and December, are 

 slightly more developed in the fish of 

 February, March, and so on. In May 

 their state of maturity is exactly the 

 same as that of the so-called "small 

 summer salmon," which then begin to 

 ascend; for both categories of fishes — 

 and the same holds good for the third 

 category, the St. Jacob salmon, which 

 ascend from July — the date of their en- 

 tering the river is, generally speaking, 

 a measure of the state of development 

 of their sexual glands. The further de- 

 velopment of these organs will take 

 place during their stay in the river 

 itself, and as these fish take no food dur- 

 ing their sojourn in the fresh water, it is at the expense of the nutritive matter 

 stored in their muscles, in the lateral muscles of the trunk especially, that the 

 maturation takes place. From this it is clear at the same time that, the "winter 

 salmon" of October and December being by far the most valuable fish of all, 

 through the year the condition of the salmon deteriorates slowly but gradually 

 until they reach maturity, with perfectly developed sexual glands (the weight of 

 which may be over 25 per cent of that of the whole fish), but otherwise in 

 extremely poor condition. 



Fig. 2. — Diagram showing the ascent of the Rhine salmon 

 in different months. The outer line, circumscribing the 

 remainder of the figure, represents the salmon of the 

 greatest size, which are called from October to April 

 winter salmon and from May to December large summer 

 salmon. The middle line represents the middle-sized 

 salmon, which are called small summer salmon. The 

 inner line represents the smallest salmon, which are called 

 St. Jacob salmon (grilse). The dotted part of each line 

 indicates when the salmon begin to ascend, the swollen 

 part when their numbers are greatest, the feathered end 

 part when they are ripe for spawning. 



