INTRODUCTION AND BREEDING OF FISH. 99 
the natives, had just been taken in the Bosphorus. They were 
alleged to have followed an English ship from the Thames, and 
to have been frequently observed by the crew during the pas- 
sage ; but I was unable to learn their specific character.* 
Many of the fish which pass the greater part of the year in 
salt water spawn in fresh, and some fresh-water species, the 
common brook-trout of New England for instance, which under 
ordinary circumstances never visit the sea, will, if transferred 
to brooks emptying directly into the ocean, go down into the 
salt water after spawning-time, and return again the next 
season. Some sea fish have been naturalized in fresh water, 
and naturalists have argued from tle character of the fish of 
Lake Baikal, and especially from the existence of the seal in 
that locality, that all its inhabitants were originally marine 
species, and have changed their habits with the gradual con- 
version of the saline waters of the lake—once, as is assumed, 
a maritime bay—into fresh.t The presence of the seal is hardly 
conclusive on this point, for it is sometimes seen in Lake Cham- 
plain at the distance of some hundreds of miles from even brack- 
ish water. One of these animals was killed on the ice in that lake 
in February, 1810, another in February, 1846,{ and remains 
of the seal have been found at other times in the same waters. 
The intentional naturalization of foreign fish, as I have said, 
has not thus far yielded important fruits; but though this par- 
* Seven or eight years ago, the Italian government imported from France 
a dredging machine for use in the harbor of La Spezia. The dredge brought 
attached to its hull a shell-fish not known in Italian waters. The mollusk, 
finding the local circumstances favorable, established itself in this new habitat, 
multiplied rapidly, and is now found almost everywhere on the west coast of 
the Peninsula, 
+ BABINET, Ltudes et Lectures, ii., pp. 108, 110. 
{ TuHomrson, Natural History of Vermont, p. 38, and Appendix, p. 13. 
There is no reason to believe that the seal breeds in Lake Champlain, but the 
individual last taken there must have been some weeks, at least, in its waters. 
Tt was killed on the ice in the widest part of the lake, on the 23d of February, 
thirteen days after the surface was entirely frozen, except the usual small 
cracks, and a month or two after the ice closed at all points north of the place 
where the seal was found. 
