From what I am led to believe, trout / salmon ages can be determined from scale samples. How accurate is this method and do the scales have to be examined under a microscope ?

A scale sample from a Dentex around 7lbs I caught in the Canaries a few years ago was held up to the light by the guide and he gave us an estimation of it's age. Was the guide doing a Crocodile Dundee style stunt or was it the real deal ?

With Sea trout caught in fresh water, the number of times they have run to the sea can apparently be determined by scale samples. Can anyone explain how this is done i.e. how do the saltwater circuli vary from the freshwater ones ?

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Tight Lines. :)

Can only be done under a microscope, unless the fish has a particularly large scale.

scale reading

Fine, unless they are stockies in which case it's a waste of effort. Also, you need a reasonable number of scales - half a dozen should do - to make sure there are no replacements, and then you need to know exactly what you are looking for. Not as easy as it sounds - and I have looked at thousands of scales from all species of fish.

Hi', I might very well come unstuck here, and it would probably be safer to google an answer; but basically the rings on a fish scale can be used to tell its age by counting them; a rapid growth ring, which is broader, would suggest a year at sea for a migratory fish ( good feeding), while an eroded ring indicates spawning. That is a very rough description, and I am sure there are those who will fault it. TC
The American writer, the late, Ed Hewitt has numerous enlarged pictures of scales in his book on fly fishing.

this is done at faskally at pitlochry where the the biologists deternine age ,sex for fish scales