Neretva is a unique jewel of nature and together with Buna River and Trebizat, one of the last shelters of the famous Softmouth Trout in the region.
Softmouth trout only exist in some rivers of the western Balkans that drain into the Adriatic Sea. Heckel was the first to describe this species from three localities.
The rivers Zrmanja, Jadro and Vrljika as Salar obtusirostris in 1851. Later on, the fish was found also in the Krka River in Dalmatia – Salmo obtusirostris krkensis (Karaman, 1927), in the Neretva river system – Salmo obtusirostris oxyrhynchus (Steindachner, 1882) from the River Neretva, and in the Zeta River in Montenegro – Salmo obtusirostris zetensis (Hadžišče, 1961).
The softmouth trout is characterized by its striking similarity in appearance to both trout and grayling. Its most peculiar morphological characteristics are an elongated snout, a small and flashy mouth, relatively large scales and high body depth.
It is a spring spawning obligatory freshwater fish. Maximum size and weight: 50 cm, 5 kg. The Neretva softmouth trout shows the most pronounced morphological characteristics featuring the softmouth trout; all the other subspecies are more brown trout-like.
Neretva soft mouth trout (Salmo obtusirostris oxyrhynchus) with a nickname “Meka” coexisted in the Neretva with native brown and marble trout for thousands of years. It was largely successful enough in avoiding inter-species hybridisation. Thus far has maintained its identity.
This is probably due to different spawning times and possibly different spawning ground
Again similar to grayling, softmouth trout feed on fauna found in the bottom sediments of rivers and lakes, being so called benthos feeders, and show generally grayling-like feeding behaviour.
They usually hold in the deep pools in rivers, not near the banks like brown trout often do. Softmouth trout exclusively populate rivers where grayling were never present, or were never native, for example the Neretva River, where grayling are an introduced species.
However, grayling and softmouth trout are not able to hybridize, which is a proof of their distant relationship. So it seems that softmouth trout evolved some grayling-like characteristics because they required these characteristics to survive in a grayling-free niche.