The fish fauna of the Neretva river basin in the western Balkans is representative of the Dinaric karst region and characterized by several endemic and endangered species.
The river Neretva and its tributaries represent the main drainage system in the east Adriatic watershed and the foremost ichthyofaunal habitat of the region.
Numerous species live in very narrow and limited areas and are vulnerable, so they are included on the Red List of endangered fish of the IUCN.
According to Smith & Darwall (2006) the Neretva River, together with four other areas in the Mediterranean, has the largest number of threatened freshwater fish species.
[2] The Neretva river with its many tributaries, lakes and marshes provides rich freshwater habitat for its native, as well as for introduced non-native fish species.
In the middle section of the watershed remoteness and ruggedness of the terrain gets even more extreme, especially around small river tributaries, mountain creeks and lakes, however the Neretva river itself is completely flooded throughout entire midsection with four large artificial lakes, and intersected with four large dams.
More downstream in the lower reaches (Lower Neretva), the Neretva basin and the river itself comprise remarkable landscape, in which valley from the confluence of its main tributaries of the section, the Buna, the Trebižat and Bregava rivers, then spreads into an alluvial fan, covering more than 20,000 hectares, with specious flat plains or poljes, where water-flow is slow but abundant, with many branches often widened into natural lakes and marshes, and constantly replenished with much fresh water from numerous large karstic well-springs.
The fast pace of the pike-perch population growth and displacements in the Neretva River basin is expected to match the environmental conditions from the mid-ecological valence of this fish.
Parallel with the increase of population of pike-perch in the Neretva lakes is the obvious decrease in the quantity of indigenous species like the European chub (Squalius cephalus), and the disappearance of rare and endemic species like Adriatic dace (Squalius svallize), Neretvan softmouth trout (Salmothymus obtusirostris oxyrhinchus) and marble trout (Salmo marmoratus).
On the basis of all relevant indicators it is necessarily to take urgent measures, continuous and organized action, to dramatically reduce the quantity (if is not possible to exterminate) of this allochthonous type of fish, as well as to attempt to revitalize autochthonal fish populations, with fish stocking of local, especially salmonids species, all in order to prevent the same fatal experience with the water ecosystem in the UK, and prevent, if possible, this type of allochthonous species colonization of the Neretva River basins with irreversible effects.