The sea trout is in fact the
same species as a brown trout salmo trutta.
The sea trout is simply the migratory form. Like
the salmon a brown trout can be anadromous. In
English this means that it spawns in fresh water
but migrates to the sea for feeding.
Not all brown trout become sea
trout. In fact nobody is sure why some do and
others don't. It may be partly genetic and partly
environment driven. Certainly waters where feeding
is relatively poor seem to produce more sea trout.
Since mature trout are territorial it is thought
that the weaker fish are forced downstream by
the stronger ones. Eventually they reach the richer
feeding in the sea and start to grow more quickly.
You might also come across bull
trout. These never go to sea proper, but hang
about the estuaries. Again they grow faster. Sea
trout don't venture so far out to sea.
Whereas salmon will venture out
to the Faroes and Greenland, the sea trout tend
to hand around the coasts. This probably explains
why sea trout are more susceptible to sea lice
infestations from fish farms which are found around