![Sample our Earth Sciences journals, sign in here to start your access, latest two full volumes FREE to you for 14 days]({"type":"image" , "src" : "/sda/5930/TOC-Subject-Sample-2021-Earth-Sciences.jpg"})
Summary
The considerable changes of the hydrofauna are closely connected with the intensive development of industry, agriculture and the acclimatization of new hydrobionts.
The constant regulation of the water level, the increasing water pollution of some rivers led to the important diminution of migratory fish stocks: Alosa fallax, Salmo salar, S. trutta, S. trutta m. fario, Coregonus lavaretus, Vimba vimba, Lampetra fluviatilis. The stocks of Acipenser sturio and Petromyzon marinus are now extremely small. The stock of Abramis sapa has entirely disappeared. Coregonus lavaretus holsatus is rarely met.
From existing 60 species of fishes in Lithuania are 48 native and 12 introduced species (Cyprinus carpio, Acipenser ruthenus, Salmo fontinalis, S. gairdneri, Coregonus nasus, C. peled, C. lavaretus maraenoides, Carassius auratus gibelio, Ctenopharyngodon ideila, Hypophthalmichtys molitrix et al.).
The stocks of crayfish (Astacus astacus) are on the way to diminution, they were ousted by Astacus leptodactylus.
In eutrophicated lakes Pontoporeia affinis, Mysis oculata v. relicta and Limnocalanus grimaldii v. macrurus are disappearing. By natural way from Ponto-Caspian Waters Dreissena polymorpha, Theodoxus pallosi, Cordylophora caspia, Corophium curvispinum and Chaetogammarus ischnus have penetrated. In 1960 were successfully acclimatizated Mesomysis kowalewskyi, Limnomysis benedeni, Hemimysis anomala, Pontogammarus robustoides P. r. aestuarius, P. crassus and Chaetogammarus warpachowskyi.