the Residence of certain Fishes. 217 
water of the Thames; although it is not ascertained whether it re- 
mains for any length of time out of the salt or brackish water. The 
C. Alosa, however, or shad, ascends rivers to spawn in the spring, 
like the salmon, returning in the autumn ; and its spawn, the white- 
bait of London epicures, is well known to be taken in the fresh 
water. It is probable therefore that it spawns there, as the salmon 
does; and hence also, were this fish worth the experiment, it 
might probably be naturalized to lakes and ponds. This seems 
peculiarly plausible in the case of all the sea-fish which spawn in 
fresh waters; because this is one of the natural operations which 
we should conceive it 2 priori, most difficult to counteract. 
I already noticed that the best known fish of this genus, the 
herring, was found in the fresh American rivers. And though I 
was obliged to contradict M. Nouel respecting its existence in 
Loch Lomond, I may here say that it has been found at different 
times in Loch Dhu, a fresh water lake in Argyllshire, near Loch 
Fyne. In this case, it appears to have been introduced during a 
flood, through the small river by which this piece of water commu- 
nicates with the sea; being afterwards confined by the subsidence 
of the water, so as to have remained imprisoned for many years. It 
does not seem however to have been ascertained whether or not it 
propagated in the lake; so that this natural experiment still re- 
mains incomplete for want of observation. This however is a 
trial so easily repeated, that nothing probably has prevented it, but 
that ignorance or prejudice on this subject which it is the main ob- 
ject of this paper to remove, by holding out reasons for probable 
success. 
The Crucian, Cyprinus Carassius, the Bleak, C. Alburnus, the 
roach, C. Rutilus, the bream, C. Brama, the C. Idus, C. Nasus, C. 
Aspius, and C, Ballerus, like the pike, seem to inhabit the Caspian 
sea as well as the fresh waters and ponds of Europe; offering 
other instances of perfect and permanent indifference to the nature 
of the waters in which they exist. 
The Chaleoides, in the same genus, migrates annually from the 
same salt lake to the rivers that run into it; and the C, Aphya 
