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- 
monide, 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 m 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 ceconomy 
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. 
