Grayling (Thymallus thymallus) are a beautiful fish, famous for their delicate taste for the smallest or most peculiar of flies. Luckily this is only true in autumn, when their bellies are full after bountiful summer, but in the spring, after their spawning, they are anything but picky.
The Slovenian rivers Sava, Radovna and Kolpa still hold some exceptionally big grayling, but generally the trend for this species is in decline. In the recent decade, due to the trend of rising river water temperatures and stocking of large amounts of rainbow trout in combination with river regulation construction works, they have become increasingly rare. Despite all of that, there are still stretches with healthily and viable populations where fishermen get see these silver knights up close.
To make things even more interesting, there is a second type of grayling swimming in Slovenian rivers. Rivers of the Adriatic Basin hold the Adriatic grayling, which is known by its different coloration of caudal fin; they tend to have a more greyish fin compared to the Danubian population. But similar to the situation of the marble trout, people have brough grayling of this Danubian population into this catchment and since they can reproduce, the Soča is now home to many grayling hybrids. In the last decade there have been quite some studies done on figuring out the distinctive differences on morphological and genetical levels, trying to figure out the variations between the two species/types of grayling. And they are currently searching for ways to help protect the Adriatic grayling in order to fix the mistakes from the past.
