Going down the aquarium, after trout zone we reach grayling zone. The bottom is more gravely, and submerged plants are flexible, which protects them from breaking. The main representative is the fish grayling. This species feeds on small invertebrates which live at the river bottom, for example caddisflies which build little houses from rocks and twigs to increase their weight and prevent water from taking them away. Along with grayling, there is our largest trout species huchen, which is also known under the name the Danube salmon. Allegedly the largest specimen caught in Croatia in the river Sava weighed around 50 kilograms. This species is endemic to the Danube Basin and it is endangered in Croatia. Considering it mainly hunts in cold winter months, search for this so called river queen represents a passionate challenge to anglers. Huchen feeds on fish from top and bottom river layers, depending on its migration.