a biotope is a reproduction of a fishes natural habitat. if you have an African Rift lake tank with plants, it's not a biotope.if you have Asian plants or fish in an Amazon tank, it's not a biotope. you can have different biotopes from the same waters. parts of the Amazon are loaded with plants, but you will never find discus in those waters. they come from the black water areas where plants, except for floating plants, can't grow. most will consider my tank to be a biotope, but it's really not because lemon tetras are not found in the same waters as discus. same river, but different habitats. a true biotope will have fish, plants, rocks, and even substrate from a certain region, but it's very rare to see a tank like that. hope this explaines it a little.