freshwater fishes sturgeon sterlet, acipenser ruthenus in clear water with shallow rock and fall leaves. top view

acipenser acipenseridae animal aquarium autumn background baerii beluga caudal caviar clear coastlines condition copy danube environmental fall fauna fin fish fishes fishing fresh freshwater gravel hatchery heterocercal huso lake landscape leaf leaves life nature outdoor pond river rock ruthenus scene scenery sea shallow space sterlet sturgeon top underwater view water wild wildlife young