THE STATE OF MIGRATORY FISH SPECIES IN OUR WATERS

Abstract

Migratory fishes are important components of the rich wildlife of our waters. Amongst them there are certain species which spend the vast majority of their lives in fresh water (catadromous) and migrate to the sea for spawning, for instance eel species. Others migrate the other way around (anadromous), spending their main growth period and reaching sexual maturity in the sea, then spawning in the freshwaters. Notable representatives of this group are salmonids and sturgeons. The populations of the aforementioned species have decreased significantly in the past decades. The reasons for this can be affected by many factors. Apart from overfishing and the spread of diseases, the dams built on rivers, posing artificial obstacles greatly hinder the achievement of a sufficient natural growth. The outdated dams make approaching the spawning grounds impossible for the fish striving to get there. Having noticed this adverse effect on biodiversity, many of these obsolete dams have already been removed. Where the opportunity arose, fish ladders were constructed, which facilitate the movement of fish. Besides helping the migration, fish ladders provide many species with a habitat.