A much argued topic is that of, “Is it a sea trout or a brown trout?” The first problem is that they are all the same fish: Salmo trutta. Stock a river in Patagonia with brown trout and come back 10 years later and you will find sea trout. Strip a hen sea trout and fertilise the eggs with sea trout milt and seed a river, and over the following generations, some of the fish will stay put. On the redds, brown trout breed freely with sea trout. They are all the same fish. Furthermore, the term sea trout is a loosely defined one as in some places fish can migrate in and out between fresh and salt, back and forth. In other places the fish live in the estuary. The way to define a sea trout has been to measure the level of strontium in their scales. However, even that method has been questioned. So, there is no easy way. In systems such as Loch Lomond, it has been shown that there is no “black & white” between migratory sea trout and non-migratory brown trout. They show a ‘greyscale’ dynamic, with some spending much of their lives in a marine environment, while others are mostly freshwater-based, though neither by any stretch 100%.
Salmo trutta is described as a species that shows ‘partial migration’. However, as anglers, we are forever asking ourselves, is it a brownie or a sea trout??? It’s hard not to ask, when it’s a greyscale thing. I collected together the various photographs I have accumulated from what can be regarded as ‘Sea trout lochs’ and ‘Sea trout rivers’. I present them here. I recognised certain features that I could group them by, such as, “Gill/body demarcation, with grey body”, and “Pollack”, where the fish just reminds me of a pollack, whether it has anything to do with where it has been living or not! the gill demarcation is an observation I make again and again where the head is often near to the colour of a brown trout, but the colour changes at the gill cover edge and the body is more sea trout colours. Some folk reckon some of these are brown trout, but I don’t think I see brown trout with the same colour change at the gill cover edge???
Some of the fish grouped under “Gold” will I am sure get some folk reclassifying them as non-migratory fish. But if they are non-migratory, why is it they are not there outside of the times when sea trout are running?
When sea trout come into freshwater, they abandon the silver colouration adopted by pelagic sea fish such as bass and herring, required to disperse reflected light (to adopt a ‘cloak of invisibility’), and they revert to the brown trout colouration required to camouflage them against their background. They are, underneath their sea-going silver colouration, brown trout!
There are fish in my collection that are classed as “white trout” – they were at sea, they came into freshwater to spawn, and post-kelt period, but prior to returning to sea, they have silvered-up… to the point of being more silvery than many fresh-running fish!
So, for what it’s worth, here is my collection of photographs, of what are, largely, migratory trout, with room for argument. Before grouping them, I wrote down 10 spaces for them and, as I pigeon-holed them, the 10 classes seemed to work out OK, so I just went for it. It is totally arbitrary, and could be regrouped 100 times over. Also, many of the fish could be moved about from group to group. It is what it is…