Sturgeon - This fish is probably responsible for some sightings of lake monsters. Sturgeon (Acipenser) is a genus of fish, of which some twenty different species are known, from European, Asiatic and North American rivers. They pass a great part of the year in the sea, but periodically ascend large rivers, some in spring to deposit their spawn, others later in the season for some purpose unknown; only a few of the species are exclusively confined to fresh water. No species occur in the tropics or in the southern hemisphere 固opFoto / Fortean