Sounds interesting Rob, not heard of Leopard Trout, Tiger Trout yes. Sounds like 'local' terms for variation ?
Could be gene flow caused by stocking, or more likely natural diversity. It is in a populations interest to have natural variation or diversity - this is how speciation actually starts, and explains why some Brown Trout are sea run and others are river dwellers (though these are not classed as species). Some land locked lochs also seem to have a variety of Trout - some silver Loch Leven types, some yellow bellied etc which could be natural variation or due to whether or not stocking has occured in the past, or a combination of the two ? The two 'types', or sub-species, of Arctic Charr that were discovered in Loch Ness in the 80's is another example.
I raised the (possibly unpopular !) issue of stocking the Don with 'non genetic' stock in the recent thread Trout and Salmon Sunday Fishing Letter, and how this may not be as damaging as some may think, maybe not even at all if it is limited (which it was) - having some gene flow between populations can be beneficial and is something that seems to occur naturally within some populations. We might not even actually be able to define the pure 'genetic stock' of Don Trout anyway, but then again that doesn't mean that there isn't one, just that we can't 'measure' it !
Crossbills in Scotland fall in to 3, possibly even 4 types, 3 of which are recognized and categorized as 3 distinct 'species'. DnA studies show no significant genetic distinction between the three 'species', which suggest they do not breed in total assortative isolation, but that there must be some gene flow between the three 'species' or types. In theory they could be sub-species, though I accept that they are acting as 'species'. This adapts the population as a whole, and within each species category, to all environmental possibilities that may present themselves, including adverse ones - basically, it is Natural Selection ala Charles Darwin. I don't doubt that some trout populations that have access to the sea are potentially similar - a Dee Trout could breed in the Don, with a Don Trout and vice versa, even Tweed ones have been caught in the Ythan ( It think ??). If anyone has evidence of this (or not !) I'd be interested to hear.
Some river populations of Brown Trout are potentially a biological and genetic 'soup', and may be better equiped as a result of this diversity and variation, some of which occurs naturally ! Tell that to Mr. Thornton....actually don't or there'll be another letter next month !!
Lindsay
