This zone is characterised by vegetation of swimming hydrophytes which spread their roots on the bottom and develop leaves and flowers on the water surface. Midges, snails and shellfish are distinguished among invertebrates. Most fish species live in the barbell zone, and all fish in the rivers around Karlovac belong to this zone. Here you can see chubs, common daces, asps, nases, vimba breams, bleaks and spined loaches. Interestingly, the asp is the only true predator from the family of carps. Main feature of these fish is that, unlike trout, they do not need a lot of oxygen that white waters usually abound in. Some fish species in the barbell zone are omnivores, which means that, beside fish, they also feed on algae and invertebrates. Chub is one of such fish species. Another species of fish which also comes to this zone is grass carp, a herbivore native to Chinese rivers and their basins.