Discus
Published
The discus is a fish people work up to. Its flat, round body, slow, graceful swimming and colours from wild brown to vivid turquoise and red have earned it the name "king of the aquarium" — and its demands on water quality have earned it a reputation as a fish for experienced keepers.
Where discus come from
Wild discus live in the Amazon basin, in floodplain lakes and slow side waters where they shelter among the branches and roots of drowned trees. The water is warm, very soft and acidic, and often stained dark by leaves. How many species there are is still argued over: most scientists accept two or three, among them the Heckel discus (S. discus), recognisable by its one bold dark bar across the middle of the body.
Bred for colour
Wild discus are brownish, greenish or bluish, with nine dark vertical bars and wavy blue lines over the body. Breeders in Germany and later in Asia have spent decades turning these into domestic forms: turquoise and blue diamond fish covered almost entirely in blue-green, red-orange pigeon bloods with fine dark speckling, pale snow whites, red melons and spotted leopards. The bars can still darken and lighten with the fish's mood.
Raising the young on their skin
Discus parents form pairs, lay their eggs on a vertical surface such as a leaf or root, and guard them together. Once the fry are swimming, they do something rare among fish: for the first weeks the young feed on a special mucus that both parents produce on their skin, swapping from one parent to the other. It is one of the reasons discus breeding is so admired.
Keeping discus
Discus need a large, tall tank — they are big, round fish — kept warmer than most tropical tanks, with soft water and very clean conditions. Many keepers change a large part of the water every few days. They are social and do poorly alone or in pairs outside of breeding, so a group of five or more is best, together with calm tank mates that tolerate the heat, such as cardinal tetras or some cories. Stress shows quickly: dark colours, hiding and refusing food.