Jadro is a typical karst river, short but rich in water, with an average flow speed of 9m3/s. Nobody has discovered any subterranean labyrinths through which its waters flow or answered the question of how did it has managed to find its way through the hard rocks of the Mosor Mountain and emerge on the surface. It is approximately four and a half kilometers long and springs from below the western slopes of the Mosor Mountain. The river flows into the sea in the Vranjic Bay near Solin. It has no contact with any other watercourse and this isolation, like in any other karst river, has led to the formation of a number of endemic species.

This is how the softmouth trout (Salmothymus obtusirostris salonitana), a rare and potentially endangered endemic trout subspecies formed in the Jadro River. The population of this trout subspecies has been maintained, but their accurate number is unknown.
Salmothymus obtusirostris salonitana (Karaman, 1927), the Solin softmouth trout* 

Morphology

Dorsal fin: 4 hard spines / 11 soft spines
Caudal fin: 4 hard spines / 9 soft spines
Anal fins: 2 hard spines / 8 soft spines
Pelvic fins: 1 hard spine / 12 soft spines
Number of scales in the lateral line: 100-105
Number of scales above the lateral line: 20
Number of scales below the lateral line: 17
Pyloric caeca: between 61 and 81
This subspecies has a relatively small and fleshy mouth. The snout is rounded. The bones of the upper jaw are short and wide. The upper jaw is short and barely reaches the horizontal middle of the eye. The teeth are small and the scales are relatively large. The back is grey and yellow, without spots, while the sides have dark and red spots. The dark spots are present only on the front part of the body, generally not extending beyond the area below the dorsal fin, while the red spots are present on the entire body. The operculum has more dark spots which also have the most intensive color.
Maximum size: about 2 kg; 4 kg maximum
Biology: Lives in quiet river areas. Feeds on small gammarus, small snails and catches the insects that fall onto the water surface. Breeds in spring.
Distribution: Can be found as an endemic species in the Jadro and Žrnovnica rivers. Endemic species
Endangered status: Found in the Croatian Book of Endangered Species as a threatened specie.