The marble trout is a unique trout that can only be found in certain river basins in Eastern Europe, most famously in the Po and the Soča rivers. However, marble trout can be found in certain tributaries to these basins in Italy, Croatia, Boznia & Herzegovina, and Montenegro.
They are called marble trout because of their distinct pattern, which takes on a wavy, almost tiger trout look. Depending on their environment, marble trout can develop red spots or varying skin pigmentations, which is illustrated in the pictures below. It is said that the marble trout evolved from the brown trout.
It is a fairly threatened trout, and suffers the usual problems of habitat loss and interbreeding/ competition with non indigenous stocked trout. Young marble trout tend to feed on nymphs and dry flies, but when they reach a certain size they become piscivorous (eating mainly fish).
Featured image by @aymeric_anth.