About Discus Fish
Discus are freshwater cichlid fishes native to the Amazon River basin. Discus belong to the genus Symphysodon, which currently includes three species:
The red discus or common discus (Symphysodon discus), The blue discus (Symphysodon aequifasciatus), and a new species which has been named
Symphysodon tarzoo
Like cichlids from the genus Pterophyllum, all Symphysodon species have a laterally compressed body shape. In contrast to Pterophyllum, however, extended finnage is absent giving Symphysodon a more rounded shape. It is this body shape from which their common name, "discus" is derived. The sides of the fish are frequently patterned in shades of green, red, brown, and blue. The height and length of the grown fish are both about 20–25 cm (8–10 in).
Another characteristic of Symphysodon species are their care for the larvae. As for most cichlids, brood care is highly developed with both the parents caring for the young. Additionally, adult discus produce a secretion through their skin, off which the larvae live during their first few days. This behaviour has also been observed for Uaru species.
In the wild they are opportunistic omnivores and their diet consists of invertebrates, small fish and plants. The waters from which discus hail are typically slow-moving, soft and slightly acidic (1 - 5 dGH, pH 4.0 – 6.5). Temperature of the water in their natural habitat varies from 25 – 30 C ( 82-86 F).
Common Colour Varieties
There are three layers of colour on discus:
The base colour (which usually ranges from cream to red-brown), the secondary colour (a metallic colour, usually a blue or green colour) and the black pigment that makes up the black vertical bars and allows the fish to darken and lighten at will. 
Most discus strains have either a golden or reddish base colour. The secondary colour is often striped down the sides of the fish, although many strains (such as 'solid cobalt' or 'blue diamonds') have secondary colour that eventually covers most or all of the fish's body.
There are no rules or authorities on what constitutes a unique colour variety or what to call it. A particular form may or may not breed 'true' (with offspring very closely resembling the patterns of their parents.)
Generally all of the common, established forms breed true. The exact patterning of the secondary (blue/green) colour is like a fingerprint; it develops chemically rather than being set precisely by genetics . The offspring of two 'spotted' discus will likely have spots, but not in the exact same size/position as their parents
Other Varieties
Brown:
The most common colour form in the wild; these fish have a brownish base colour with minimal stripes of secondary colour only along the head and fins.
Blue/Green:
Similar to the Brown, but with more secondary colour (either bluish or greenish.)
Royal Blue:
The secondary colour forms stripes across the entire body, with a golden base colour. These splendid fish are the basis of many of the developed colour strains, and are primarily responsible for the early fame of discus. Royal Blues can usually be readily distinguished from selectively bred colour forms by their less even base colour, with the golden colour becoming a brighter yellow around the breast area.
Red Spotted Green:
A reddish base colour with greenish secondary colour with 'holes' in it (producing spots of the red base colour showing through.) This handsome colour form is extremely rare in the wild, but is produced by several breeders.
Heckel:
Possibly a separate species, Heckels are identifiable by two vertical black bars that are much thicker than the others.
