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  23.06.2020, 08:11h


In the second sequel, the Krka Wild Nature dives below the surface and presents fish

 

In the second film from the documentary series Wild World of Krka National Park, we return to where it all began, the water. This time, Mégane Chêne and Florian Launette have taken hold of the cameras to introduce us to – the fish.

Fish (Pisces) is the largest group of vertebrates, with about 28,000 known taxa. Endemic and rare freshwater fish are the result of the geological past of the river, and in the ichthyological sense, the Krka River is a natural monument of the highest national and international value. There are 31 species of fish inhabiting the Krka River, 20.7% of the total number of fish recorded in Croatian freshwaters. Of these, 12 species (40%) are endemic: 9 are endemic to the Adriatic basin, and three are endemic (stenoendemic) to the Krka River: Visovac trout, Krka softmouth trout and Visovac goby. By definition, a stenoendemic species is an endemic species with a very limited distribution range. Stenoendemics are usually localised to very small areas, such as one mountain, one canyon, and island group, etc. That is why protecting these species is of the utmost importance.

When arriving at Krka National Park, visitors enter into a completely different world from their daily life. In watching the river, they will instantly notice the many fish in the water, which can be observed as they walk along the trails. In the Krka River upstream of Roški slap, the water is faster and colder, and so it is dominated by trout, while downstream, in the lake-like sections of the river, cyprinids are most abundant.

Let us dive in for a moment.

The fish are masters of the aquatic medium, moving with agility through the aquatic plants that are so important, because this is where most species lay their eggs. Thanks to the largest organ in the fish – the swim bladder – they can sometimes be near the river bottom, or swim at the top of the water column. The swim bladder is filled with gas in the combination of 83% nitrogen, 2% carbon dioxide and 15% oxygen, and it serves to maintain balance. When the swim bladder is contracted, the fish swims towards the bottom, while expanding it will raise the fish towards the surface. Along the long, cylindrical, laterally flattened body is the lateral line – a stripe filled with neuromasts. These are sensory cells that enable the fish to assess the strength and direction of water flow, and to detect and avoid hard objects in the water.

Today, fish are threatened by organic pollution and habitat change (particularly watercourse regulation, dam construction and hydropower plants). Fish are important bioindicators of the environment, and so the large number of fish taxa in Krka National Park is an excellent indicator of the preserved quality of the water in the Krka River.

Watch the documentary film on fish here.