For such an often strikingly beautiful fish, given the vast diversity of both pattern and colouration, it seems strange for it to have been named rather modestly simply as a Brown Trout.
Whilst Brown Trout generally have dark brown backs, lighter flanks often bejewelled with black and/or red spots, pale bellies and dark reddish brown fins they also possess the ability to change their appearance by rearranging the pigment distribution of their chromatophoric skin cells.
This inherent genetic ability allows them to alter their appearance and blend in with their surrounding environs and thus help avoid detection and predation. Brown Trout are also capable of becoming darker when aggressive and lighter when submissive.
These colour changing chromotophore cells can also be found in amphibians, reptiles, crustaceans and cephalopods such as octopus, squid and cuttlefish. This appearance altering ability goes some way to explain the diverse colouration and markings we find in our Brown Trout. These variations can range from the dull dark stunted trout lurking in the shadows of a low nutrient acidic highland lochan to the magnificant deep golden bronze yellow bellied specimens with their sides bedecked with black, red and sometimes even blue spots to be found in waters with better feeding.
With all this diversity it's perhaps easy to understand the earlier belief that we were in fact dealing with differing species. Whilst some Brown Trout can and do spend their entire life cycle in the same stretch of river they were born many others migrate from rivers and streams to lochs and estuaries before returning to spawn.
It's worth reminding ourselves at this point that our Brown Trout and the anadromous Sea Trout are in fact genetically exactly the same species with the latter taking the decision, for a variety of reasons, to make the journey to sea where they grow large on a much richer marine diet.
Also, with them being the same species, it will come as no surprise that they can interbreed without issue.
Yet another behavioral variation is the Brown Trout that - whilst not migrating to a fully marine environment like the Sea Trout – is content to move back and fore between the tides and feed in both freshwater and estuary, these trout are known rather unkindly I might suggest as “slob” trout.
Once thought - yet again - to be an entirely different species, the Slob Trout, due to its physiology is capable of thriving in the brackish estuarial environment. These Slob Trout, unlike the Sea Trout, do not go through the process of smoltification.
These superbly proportioned Slob Trout ~ fuelled by the highly nutritious feeding in the estuary where shrimp, sand eel and small fish can be found in abundance ~ are an incredible sport fish often reach considerable size with three to four pound trout and beyond not uncommon.
For some considerable time there were also heated exchanges between contradicting held scientific viewpoints regarding whether Ferox Trout were simply Brown Trout who had grown large having switched to a predominantly fish diet. This train of thought has however been dismissed and it has now been agreed and accepted that Brown Trout and Ferox Trout are in fact separate species.
Our Brown Trout, or “brownies” as they are affectionately known, have one of the greatest levels of genetic variation seen in any invertebrate with trout having between 38 and 42 pairs of chromosomes whereas humans have only 23 pairs which means that there are more diverse genetic variations in our wild Brown Trout than there are in the entire human race.
More to follow shortly ;o)
