246 Mr. J. Blackwall on the Salmon and Bull-trout. 
observation. Trout, suddenly transferred from their natural 
haunts into wooden, metallic or earthenware vessels supplied 
with water recently taken from the same stream in which they 
were captured, speedily assume a lighter hue; and as this change 
does not appear wholly to depend upon the colour or capacity 
of the vessels in which they are placed, I am inclined to attribute 
it primarily to the influence of fear, and in this opinion I am the 
more confirmed from having frequently perceived a similar 
transition in the hue of salmon soon after they have been hooked 
by the angler. That this is not the sole occasion of sudden 
alterations in the colour of fish I readily admit, for I have often 
disturbed small flounders in the Conway, which on changing 
their situation and reposing upon objects of a different hue from 
those they had last quitted, soon became accommodated to this 
circumstance of their novel position by undergoing a modification 
of shade which harmonized with that of their resting-place and 
effectually served to conceal them from ordinary observation. 
Even death, as the disciples of Isaac Walton are well-aware, and 
as the following anecdote clearly proves, does not immediately 
put a stop to this chameleon-like transition of tint. 
A gentleman of my acquaintance, a proficient in the art of fly- 
fishing, had taken a young salmon weighing about a pound and 
a half, which, in consequence of having been a long time in the 
fresh water, had lost its brilliancy and had acquired a very dark 
aspect ; this fish one of my children requested to be permitted to 
carry, so after having inserted the longer and smaller end of a 
slender forked twig under one of the gill-covers and drawn it 
through the mouth till the prize was retained in the angle formed 
by the fork, I gave it to the boy, who held it suspended with the 
tail downwards. After the lapse of several minutes, perceiving 
that the fish had lost all its blackness and had become perfectly 
bright, I directed the attention of my acquaintance to it, who 
could scarcely be persuaded that it was the same which he had 
captured a short time before, but supposed that I had secretly 
substituted another for it ; however, the speedy resumption of its 
former dark complexion, which underwent no further mutation, 
completely convinced him of its identity. 
I shall not attempt to offer any explanation of the remarkable 
physiological phenomenon here recorded; but, apart from the 
mysterious operation of psychological agency, its cause must un- 
doubtedly be sought for in the organization of the rete mucosum. 
