Introduction, Intervention and Invasion

3.1. Introduction, Intervention and Invasion

To preserve and increase valuable fish stocks certain fish species inhabiting one water reservoir are introduced into another water reservoir or water basins with similar living conditions.

Introduced species are fish species introduced into natural water basins for fish-breeding purposes as well as with a view to increasing fish yields. In the case of the Dnipro Basin, these include 9 fish species: Cyprinus carpio, Carassius auratus gibelio, Ctenopharyngodon idella, Aristichthys nobilis, Hypophthalmichthys molitrix, Ictalurus nebulosus,Ictalurus punctatus, Anguilla anguilla, and Solmo gairdneri irrides.

Species Diversity of Cyclostoma and Fish Inhabiting the Dnipro Basin

Remark: “х” – available; “ “ – unavailable; “?” – no evidence

Apart from fish, feed organisms too were introduced into the Dnipro Basin water reservoirs. Thus, the Dnipro reservoir was stocked with sandhoppers and mollusks, while the Kremenchuk reservoir was stocked with Gammaridae. To improve the feed base of Ctenopharyngodon idella and the spawning environment of native fish species the Kremenchuk water reservoir was stocked with broad-leaved Zizania.

Interventionist species are represented by eurybiont species which can, in particular under the influence of anthropogenic factors, actively and substantially expand their areal.

The interventionist species dwelling in the Belarus Dnipro Basin include 4 species, namely, Gasterosteus aculeatus L., Pungitius pungitius pungitius (L.), Neogobius gymnotrachelus (Kessler), and Neogobius melanostomus (Pallas). The Ukrainian Dnipro Basin is home for 7 interventionist species, namely, Gasterosteus aculeatus L., Сlupeonella cultriventris cultriventris (Nordmann), Syngnathus nigrolineatus Eichwald, Neogobius iljini Vasiljeva et Vasiljev, Neogobius melanostomus (Pallas)., Proterorhinus marmoratus (Pallas), and Benthophilus stellatus (Sauvage).

Interventionist fish species inhabiting the ponds and watercourses of the Dnipro, Desna, Seim and Psiol sub-basins on the Russian Territory have as yet not been studied.

Apart from interventionist fish species, the other species that have become widespread in throughout the Dnipro Basin are invertebrates of the pontocaspian complex. Some interventionists (i.e. mollusks such as Dreissena bugesis and Polymorpha, Monodacna, Pontogammarus-meoticus, Crassius, Robustoides, Polychaeta hypania, etc.) have become predominant having formed new communities. As vast areas of the bottom of the Dnipro Basin water reservoirs have become populated by large numbers of mollusks of the Dreissena type for the first time in the history of the hydrosphere there has appeared and has been detected a new type of freshwater communities with an attached filtering mollusk acting as a medium-forming dominant organism. So far we do not fully understand the implications of the development of this new community type, which has its own unique topical, trophic and other cenotic links in freshwater ecosystems. However, within the scope of this Project we can say that most benthos-eating fish species in the Dnipro reservoirs have switched over not only to the Dreissena itself but also to the companion species.

Invasive species are those which have been accidentally introduced into natural water basins in the course of fish-farming activities or as a result of illegal introduction and do not belong to fish-breeding objects. The invasive species dwelling in the Belarus Dnipro Basin include 2 species, namely, Perccottus glenii and Pseudorasbora parva. On the Russian territory these are Perccottus glenii and 2 species of Tilapia, while in Ukraine these are Perccottus glenii, Pseudorasbora parva and Lepomis macrochirus (Rafinesque).

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