The Salmon Rivers of Scotland
Derek Mills & Neil Graesser ©1992
ISBN 0-7063-6929-7

pg. 1 Upon approaching freshwater, salmon stop feeding and will not feed again until it returns to salt water, if they do - possibly up to a year later.

pg. 2 The return to the "home" stream was established by 1653 by 'tying a riband or some known tape or thread in the (tail) of smolts and catching them again when they came back to the same place usually six months after'.

The leading theory for finding the "home" stream is based on smell. 

Memory may be "imprinted" a few days before leaving for saltwater, not early in life.

They move upstream, into freshwater, at dusk.
Fairly strong onshore induce movement upstream, also. 
Peak in tidal cycles seem to effect concentration and upstream runs.
Until the water reaches 42°F, there is little upstream movement of fish.

pg. 3 The adult male and female change in appearance after entering freshwater at spawning time. New bones and teeth appear, particularly in males' hooked jaw (or kype).

The salmon layes 2,000 to 15,000 eggs.

After spawning, most males die, but a relatively small proporion of females return for a second spawn.

pg.6 Salmon diseases listed.