During the 19th century the idea of the "balanced aquarium" was developed. This approach was an attempt to mimic a balanced ecosystem in nature. According to this method, fish waste could be consumed by plants, and plants along with the air surface of the water could supply oxygen for the fish. In 1869, the first tropical fish (the Paradise Fish) was imported from Asia. In these days, tropical tanks were kept warm by an open flame. Because early filters were noisy and expensive, fishkeeping was a hobby reserved for wealthy, scientifically inclined individuals.