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Discus, Queen of the Aquarium

By Neale Monks

The discus is considered by many to be the finest of all freshwater
aquarium fish. It is certainly a handsome animal; regular, wild-type
discus have a reddish-green body with an attractive pattern of electric blue markings. At about 10-12 cm in size, it is large enough to be impressive but small enough to fit into an ordinary home aquarium. In terms of behaviour it is completely peaceful, and can coexist happily with a wide variety of tankmates (though it shouldn’t be thought of as a standard issue community fish; more on this later).

On the other hand, discus are not easy fish. They are much more fussy about water chemistry and water quality than most freshwater aquarium fish, and fall prey to a variety of sicknesses

Discus in the wild
Two species of discus are known, the red discus (Symphysodon discus) and the blue discus (Symphysodon aequifasciatus). A number of subspecies have been described over the years, but these aren’t used much by scientists any more, though they may be encountered in the aquarium literature. Both species of discus are from the Amazon, where they live in fairly deep water hiding among rocks and roots.

The waters they inhabit are invariably warm, soft, and acidic, something that is of great significance when maintaining these fish at home.

Wild discus feed primarily on aquatic insects and insect larvae, but
also take a variety of small crustaceans, worms, and other animals. They also eat a little plant matter, including algae. Young discus, and adults outside of breeding condition, form large schools, but breeding adults are territorial and form pairs.

Artificial varieties
Virtually all the discus offered for sale are tank-bred rather than wild-caught fish, and a great many of these discus are artificial varieties.

These varieties include forms with names such as Blue Diamond, Snow White, and Red Leopard. Normally, the first part of the name indicates the dominant colour; a Blue Diamond for example is electric blue. The second part of the name often refers to the pattern or shape of the fish. A Red Leopard is therefore a discus with red markings that instead of forming the normal stripes seen on the wild fish has short squiggles and spots more like the markings on a leopard.

Unfortunately for the aquarist, the way the various discus strains are named does vary, and some (like Pigeon Blood) can mean different things to different breeders. It is certainly possible that fish being sold under one particular name will be sold under another somewhere else. If you’re serious about keeping and breeding a single strain of discus, it’s essential to do your research first and buy the best possible stock. Discus are expensive, and true-breeding, pedigree stock even more so.

Buying discus
Regardless of whether the discus available to you are wild-caught or tank-bred, choosing healthy fish is very important. Any discus you buy should be active and feeding well. Unless you know the reputation of a mail-order supplier, discus are fish that are best bought in person so that you can observe the stock and pick out the specimens you want. Look for fish with bright eyes, good colour, and full stomachs.

Broadly speaking, wild-caught discus are the least forgiving fish and are best avoided by aquarists without plenty of experience of tank-bred discus. If you can, find discus that have been locally bred, as these will be pre-adapted to your local water conditions.

Unless otherwise stated, all the discus in your local tropical fish shop will be imported from farms in South East Asia or the United States. These may need to be adapted to your local water conditions, though your retailer may already have done this before putting them on sale. Note than some retailers hold their discus in soft water aquaria, which may complicate things further if your tank at home contains hard water.

Good discus are expensive; cheap discus may be a bargain but are more often coloured-up using hormones and colour enhancing foods. Also avoid discus being held in mixed species tanks. Discus are very sensitive to parasites and bacterial infections that other fish carry. Look for a retailer that has a good selection of healthy discus all being maintained in their own section of the shop.

Discus are best bought as juveniles. Obtain six or more specimens and raise them together, allowing them to pair off themselves. Outside of breeding time, discus are virtually impossible to sex, and therefore buying mated pairs is a bit of a gamble. Young fish will take a year or so to reach maturity, but in that time you’ll be able to learn about keeping discus and get prepared for the challenges laid on when they decide to spawn...

For the time being, keep the discus in their own aquarium and forget about adding tankmates. This way, their home aquarium can act as quarantine as well as a domicile. In some regards, discus are not difficult to accommodate.

They eat a wide variety of foods such as bloodworms and daphnia, and there also numerous discus-specific foods on the market, such as beef heart. Giving them a nice variety of foods is more important than trying to find the one perfect food for them. If in doubt, ask the retailer or breeder what they were feeding the fish, and act accordingly.

Do be careful about using live foods though, particularly tubifex worms, as these can introduce parasites of various kinds. As with any aquarium, remove uneaten food quickly.

Wild-caught discus come from very soft, acidic waters and expect the same thing in the home aquarium, but tank-bred stock is generally much more tolerant.

For most tank-bred fish, a pH of around 6-7 and a hardness up to around 10-degrees GH (moderately hard) is about right. Keeping the pH and hardness steady is important, so using some sort of pH buffer in the aquarium is very desirable.

Though there is some latitude as far as water chemistry goes, neither wild nor tank-raised discus will forgive lapses in water quality management. These fish are exceptionally intolerant of ammonium, nitrite, and nitrates. There are four keys to keeping discus: keep them in a big aquarium; maintain a low stocking density; install a high capacity filter; and perform regular water changes. If these things are done, then discus aren't especially difficult to maintain.

Discus do not like bright light; if you intend to keep them in a
planted aquarium, be sure and include lots of floating plants or species with leaves that cover the surface of the water. On the other hand, they do like high temperatures, at least 26ûC for normal maintenance and as much as 30ûC for breeding.

Discus become increasingly disease prone as nitrate levels go up. Besides the normal stuff like whitespot, the big killer is hole-in-the-head disease (also known as hexamita). This can only be reliably cured using prescription-only antibiotics, so prevention is essential.

Some aquarists have kept angelfish with discus in the past, but because the vast majority of angelfish available today have been mass produced under relatively unhealthy conditions, keeping them with discus is no longer recommended. The risk of infecting the discus with parasites or pathogens is just too high. The same goes for ram cichlids (Mikrogeophagus ramirezi), at one time a favourite discus companion.

In fact, cichlids of all types are best avoided because of the tendency of cichlids generally to bully the discus (even angelfish have been known to do this). Instead, choose species of tetra and catfish that will do well in the warm, acidic water conditions the discus enjoy.

Cardinal, rummy-nose, and bleeding heart tetras get on exceptionally well with discus and provide some complementary colour and movement.

Hatchetfish are also a nice addition, and serve as useful dither fish helping the discus feel calmer and thus more outgoing. Corydoras and Ancistrus catfish make excellent denizens for the bottom level of the aquarium.

Before adding any tankmates, be sure and check that the species in question will tolerate the high temperature of the aquarium. Many species of Corydoras and tetra need lower temperatures, as is the case with the subtropical peppered Coryodras and black phantom tetra.

Also avoid anything likely to be a fin-nipper, like serpae tetras and black widows, or are simply so large and active they will terrorize the poor discus, as is the case with silver dollars. Otocinclus catfish have been known to eat the skin from the sides of live discus, and are likewise best left out of the discus aquarium.

Discus breed in the same basic way as angelfish with one key exception: the eggs must be left with the parents because the parents feed the newly-hatched fry with special mucous produced by their skin. After forming a pair, the parents will clean a vertical surface upon which the eggs are then laid. After 3-4 days the eggs hatch and once the fry are free swimming they graze on the flanks of both parents for anything up to two months. They will also eat newly-hatched brine shrimp, with such foods being the main source of nutrition from about two weeks after hatching.

As with angelfish, the first attempts at breeding by newly-formed pairs are often a dismal failure. In fact it often takes several attempts before the fish get it right.

Find out more
This article is only a taster of the challenges and rewards that come with keeping discus. Before embarking on this aspect of the fishkeeping hobby, it is wise to read up on the subject first. Tropical Fish Finder maintains a list of some of the best discus books click here.

Discus are outstanding aquarium fish, but they are not for dabblers, and they require a significant investment of time and money. That said, they are exceptionally beautiful and it is no wonder they are often called the Queen of the Aquarium.

This article remains the copyright of Neale Monks and cannot be reproduced without his permission.

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