aggressive territorial attack of eurasian ruffe, wild freshwater fish conflict behaviour, captive omnivore predator species,

gymnocephalus cernua perciformes percidae pope adult gray dominant submissive driftwood eurasian europe ukraine coldwater adaptable water clear aqua animal beast aquatic fishkeeping hobby underwater decorative fish tank macro fauna widespread ecology threat ecosystem nature protection controlled conditions wild caught environment dark pet shop dangerous behaviour ichthyology weed space rare local deathly aquadesign wildlife interaction coexistence aggressive territorial attack ruffe freshwater conflict captive omnivore predator species european river biotope aquarium design low light mood shallow dof