Mr. J. Blackwall on the Salmon and Bull-trout. 245 



It appears then, from the physiological facts detailed above, 

 that the growth of the salmon and bull-trout during their first 

 visit to the sea is much less rapid than it is commonly supposed 

 to be; and as in the shoals of these species, which are more 

 abundant in the Conway than any of the other migratory Sal- 

 monidcE, fish may be observed presenting every gradation of size 

 from the least to the greatest, it is reasonable to infer that their 

 rate of growth is not accelerated materially at any subsequent 

 period of their existence, especially as individuals of large dimen- 

 sions are found to be very disproportionate numerically to those 

 of a small or even of an average size. 



By the cautious inspection of salmon and bull-trout in one of 

 the tributaries of the Conway running through my father^s land, 

 up which, when swollen with rain in the months of October and 

 November, they ascend for the purpose of depositing their spawn, 

 and by the frequent examination of their progeny in different 

 seasons of the year, I have satisfied myself that in their oeconomy 

 as well as in their rate of growth these species bear a close re- 

 semblance to each other. Both remain two years in the fresh 

 water after their extrication from the ovum, during which period, 

 notwithstanding the result of the conclusive experiments so 

 skilfully conducted by Mr. Shaw of Drumlanrig, they are still 

 indiscriminately named parr in this district*, and do not descend 

 to the sea till they have acquired their migratory dress or have 

 been converted into smolts, when they usually measure six or 

 seven inches in length and weigh from an ounce and a half to 

 two ounces. I have ascertained also, by the dissection of very 

 numerous specimens, that the males of the salmon and bull-trout 

 shed their milt before they make their first descent to the sea, 

 but that the females do not spawn till they return from their 

 first visit to the salt water ; indeed the ova are so little developed 

 in the month of May, at .which time the principal migration sea- 

 ward takes place, as scarcely to be discerned without the aid of 

 a magnifier. 



Among the external characters which serve to distinguish the 

 bull-trout-smolt from the salmon- smolt are a more robust and 

 trout-like figure ; a more decided prominence of the row of scales 

 forming the lateral line ; a greater number of spots below that 

 line ; a yellowish tinge on the lighter-coloured pectoral fins ; a 

 bright red tint at the extremity of the adipose fin ; and a firmer 

 adhesion of the scales to the skin. 



In conclusion, I shall briefly notice a few cases of rapid 

 changes in the colour of fish which have come under my own 



* A bull-trout in its second year more nearly resembles a trout than a 

 salmon of the same age. 



