A river never ceases to amaze. During the recent fishing trip with Claudio, we realised how the genetics of trout varies in one tiny river system immensely.
As I pointed out in the post about small stream fly fishing in Switzerland, Claudio and I were astonished how divers the appearances of trout in Switzerland are.
The trout varied in several features from one another.
First and foremost, their colouring ranged from a rather silver flank to a bright yellow. The silver coloured fish reminded us of a sea trout, although there is no sea, nor lake close to this little creek. Supposedly, the fish with a rather silver coloured flank are stocked trout. It is these trout patterns you get most used to in Switzerland while fishing.
The bright yellow trout on the other hand are probably wild fish. However, there seems to be a mix between the two of those. Some trout seem to have a yellow touch, but still keep their silver line on the side. Having not a biological background, I guess this might be due to interbreeding of those two genetically different fish, which both belong to trout species.
Another feature which already stands out from this particular trip, are the red dots. Whereas the wild fish tend to have larger red spots on their flank, the stocked generally retain smaller ones. Moreover, the wild fish even have them on their fins as it is impressively shown on the following picture.
In contrast to those large dots, the stocked trout with their silver colouration seem to have the smaller red dots. Furthermore, they lack the saturation of the red which the wild ones show off impressively.
Despite the overall colouring of the fish and the size of the dots, the amount of dots of the stocked trout usually outnumbers the wild ones.
Yet, the last fish of this trip, puzzled Claudio and me once more:
The trout had more dots than I had ever seen before. Still, its colouring must be described between silver yellowish and the red dots were not that flamboyant. I guess it is a breed between wild and stocked, which somehow must got some gens that double its amount of dots on their side.
What stroke me the most was that in another river nearby the trout look absolutely different. It was on my extended opening day expedition that I realised this. The trout in this system have white spines in their pectoral and after fin which reminds me rather of the brook trout we caught on the alpine Fishing Trip with Firebelly.
However, this stream is neither alpine nor does it have a brook trout population. Moreover, there is no way that fish migrated from the larger rivers below up this creek, because it slithers through a deep gorge with waterfalls of about 3 metres. I doubt that any fish can migrate this natural barriers.
One sad side to trout stocking is that it seems that as long as one does not use the genetically identical breed, the effort of stocking is not fruitful at all. A recent study (Full paper as PDF here) from the Canton Argovia underlined this drastically. This study showed, that releasing stocked trout into our waters does not improve the trout population as planned, it is rather counter-productive. Still, stocking trout and releasing them into our waters is the common approach to counter the declining catch numbers. Even tough there are already best practice examples on how to cope with declining fish numbers, such as stop stocking trout in Montana USA in 1974(!), Switzerland still holds on to old and in my opinion outdated traditions. We should rather focus on improving the fish habitat and drastically reduce the bag limit.
This is the video about 40 years of success since they stopped stocking trout in Montana USA:
Summary about the trout diversity in Switzerland
The trout diversity in Switzerland is large. As shown above, there are some distinctive features:
The colouring, the size and the colour of the dots, as well as the white spines of the pectoral as well as after fin.
I tried to make sense of my observations as far as I could on whether a fish is wild or not. If this is accurate I do not know. However, if you have any information on that, I would love to know them. Please write them in the comment section below or directly to firstname.lastname@example.org.