Discus (fish)

From Wikipedia, the free encyclopedia.

Discus are freshwater perciform fish, peculiar cichlids native to the Amazon River basin. There are two recognized species, both within the genus Symphysodon: the red discus or common discus (Symphysodon discus) and the blue discus (Symphysodon aequifasciatus). The two species are very similar and may interbreed, producing a number of hybrid strains. Details regarding the precise number of subspecies have not been finalised. Discus are most closely related to the genus Heros.

The first special characteristic of the discus is its flattened body shape. It is compressed from the sides to a dish or discus shape. Although patternation varies, most are showily coloured in shades of green, red, and blue. The height and length of the grown fish are both about 20–25 cm (8–10 in).

The second special characteristic of the discus is its care for the larvae. Like all cichlids, the parents care for the young but the discus has a unique way of doing so: the parents produce a secretion through their skin, off which the larvae live during their first few days. The young can be seen grazing off their parents.

The discus are shy and peaceful aquarium inhabitants. They are sensitive to stress and disturbance or lack of protection. The best cohabitants may be angelfish (although many aquarists claim that keeping them together with angelfish will introduce parasites and/or diseases in them) and small characides like tetras. The Uaru is another preferred tank-mate of the discus. However, small fish may be intimidated by the big discus fish or even eaten. Small chacarins like neon tetras are often found in the gut of wild discus, so they might not be the ideal cohabitants, but the ideal food.

Also suction mouth ancistras (plecos) prove less than ideal for discus since they often attach themselves on the sides of discus and eat their mucus membranes.

The popularity of the discus has given it its nickname among aquarists: "the King of the aquarium."

Caring for Discus

Generally, discus are considered difficult to care for and breed, but can be successfully kept by almost anybody with a little knowledge and effort. Appropriate water conditions:

• 78-88º F (26-31º C). Most people keep their discus at about 85º F (29º C).

• pH and hardness don't appear to matter (within reason) for general discus keeping. In order to spawn discus, low hardness and low to neutral (6-7) pH may be necessary for the eggs to be fertilized. Most commercially produced discus have been raised and spawned for generations in water that bears little resemblance to Amazon blackwater conditions (very low hardness, very low pH) and may successfully spawn under a broad range of water conditions.

• Pollution WILL NOT BE TOLERATED. In terms of tank conditions, this is really the big 'secret' to keeping discus healthy. Before buying your first discus, be sure your tank has a high capacity biological filter and has fully cycled (which usually takes a month or more.) Once a tank is established and stocked with discus, perform regular large water changes; at least half the tank, once a week. (Many breeders use much heavier water change schedules; as much as 3/4ths of the tank's volume every day!)

Feeding:

After keeping the water clean, feeding discus is the other challenge. They have no unique nutritional requirements; they can be raised on just about any high-protein fish food. The problem is that discus are often extremely cautious about adapting to new foods; it's not unusual for them to go for weeks without food before accepting a new type of food. Whenever you buy discus, ALWAYS ASK WHAT THE FISH ARE EATING. After starving for a month discus will almost always accept a new food, but if you're buying younger fish, that can also stunt growth. ALWAYS find out what sort of food the fish are accustomed to so you can get them eating in their new home right away. If you would prefer to feed them something else, you can then take your time to switch them over to the new food by mixing a little of it into their old food.

Lighting:

Discus appear to be indifferent to lighting; contrary to some popular opinion, extremely bright lights (for plants) do not seem to bother them. If your fish are 'jumpy' or hide most of the time, something else is wrong (they may simply not be accustomed to their new home yet.)

Buying Discus

The ideal way to buy discus is from a local breeder, where you can ask questions and see the fish first-hand. For many people, however, the only options are pet stores and mail-order. Pet stores are probably the best option if you only want one or two fish (which may be wise if you've never kept discus before.) If you're willing to buy a larger group of fish (such as in hopes of eventually getting a breeding pair), mail-order is the better bet. (The quality of the discus carried by pet stores can be quite spotty, and mail-order prices are often actually better.)

The idea of having expensive live fish shipped in by FedEx is often startling to first-time buyers, but this approach actually works extremely well; deaths are rare. None-the-less, check your breeder's policy on shipping deaths. Most breeders will refund your money if a fish arrives dead. Such overnight package shipping is expensive; within the US, expect to pay about $75 or more. Some breeders are willing to ship by slightly slower methods (such as US Express Mail), which can be less expensive. If you don't want a large number of fish and know other aquarists with an interest in discus, consider placing a group order to save on shipping.

Most discus are sold at about the 2-3" size. At this size, they will have some (but not all) of their adult coloring and markings. Some breeders will sell fish at the 1" size, which have virtually none of the adult coloring yet (but may be less expensive.) Generally, expect to pay anywhere from $18 to $40 for the more common color varieties (depending on size, type, and breeder.)

It can take up to a year for discus to fully develop the brilliant color and patterns they are famous for, making it sometimes difficult to judge juveniles.

Upon first arriving, discus are probably best kept in their own tank, where they can be closely watched and will not have any competition for food. Once the fish are eating well and seem comfortable they can be moved to other tanks (or additional tankmates added.)

Common Color Varieties

There are three layers of color on discus: The base color (which usually ranges from cream to red-brown), the secondary color (a metallic color, usually a blue or green color) 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 color. The secondary color is often striped down the sides of the fish, although many strains (such as 'solid cobalt' or 'blue diamonds') have secondary color that eventually covers most or all of the fish's body.

Notable color varieties:

Wild forms:

• Brown: The most common color form in the wild; these fish have a brownish base color with minimal stripes of secondary color only along the head and fins.

• Blue/Green: Similar to the Brown, but with more secondary color (either bluish or greenish.)

• Royal Blue: The secondary color forms stripes across the entire body, with a golden base color. These splendid fish are the basis of many of the developed color strains, and are primarily responsible for the early fame of discus. Royal Blues can usually be readily distinguished from selectively bred color forms by their less even base color, with the golden color becoming a brighter yellow around the breast area.

• Red Spotted Green: A reddish base color with greenish secondary color with 'holes' in it (producing spots of the red base color showing through.) This handsome color 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.

Common Bred forms:

• Red Turquoise: A red-brown base color with stripes of blue-green secondary color, normal black pigmentation (bars).

• Solid Cobalt: Golden or light brown base color, but when fully mature covered with a blue secondary color. Black pigmentation may be normal or incomplete (some vertical bars missing.)
• Blue Diamond: Essentially a 'solid cobalt', but the black bars have been completely removed through selective breeding. The reduction in black pigment gives these fish a bright, lighter blue color than most 'solid' discus.

• The Pigeon Blood mutants: These fish have a gene that disrupts the distribution of the black pigment. As a result, they lack vertical black bars (but often have 'freckles'). The lack of black pigment makes their base color much lighter and brighter; as a result, discus with this mutation may show brilliant red or yellow (or even pale cream) primary color. Most of these strains are no longer called 'pigeon bloods' per se, but are easily identifiable by the bright base color, freckles, and lack of black vertical bars. All pigeon bloods are the descendant of a single fish found in Eastern Asia in the 1980s. Since the trait is dominant and appears to be controlled by a single gene, fish bearing this mutation can be crossed with any other color strain to produce novel new 'pigeon blood' types. Pigeon bloods do have one drawback: They cannot darken at will (as normal discus can). This can make it difficult for them to raise fry, which are attracted to their parents by seeking out a dark object. (Normal discus darken when spawning or stressed.) The fish shown at the top of this document is a pigeon blood. (High quality pigeon blood types have few or no 'freckles'.)

• Snake-skins: These fish have a mutation that makes their patterning 'tighter'; as a result, they have about twice as many black vertical bars, but also have tighter, finer secondary color patterns than normal discus.

There are no real rules or authorities on what constitutes a unique color 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) color 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.

S. discus

The Red Discus prefer very soft, acidic water with a 4.2–6.2 pH, a water hardness of 0.0–1.0 dGH, and a temperature range of 26–30°C (79–86°F). Their native diet consists of a combination of worms, insects, crustaceans, and plants. They originate from the Negro River where it drains into the Amazon River and from the Trombetas and Abacaxis Rivers.

S. aequifasciatus

The Blue Discus prefer soft, acidic water with a 6.0–8.0 pH, a water hardness of 0.0–12.0 dGH, and a temperature range of 26–30°C (79–86°F). Their native diet consists of a combination of insects and invertebrates. Besides their popularity among aquarists, the fish are sometimes grown for food in subsistence fisheries. The fish is natively found among rock crevices and roots. They are a schooling fish except during the breeding season when the become territorial. The Blue Discus originates from the Solimões River to the Tocantins River basin.

See also: List of freshwater aquarium fish species

References

• "Symphysodon aequifasciatus". FishBase. Ed. Ranier Froese and Daniel Pauly. April 2004 version. N.p.: FishBase, 2004.
• "Symphysodon discus". FishBase. Ed. Ranier Froese and Daniel Pauly. April 2004 version. N.p.: FishBase, 2004.
• "Symphysodon" (TSN 170023). Integrated Taxonomic Information System. N.p.: Integrated Taxonomic Information System, 2004. Accessed on May 11, 2004.

External links

• Discus breeding A source of information about how you best keep and breed your discus
• DiscusForums A forum dedicated to the Discus
• Discus Fanatics A website dedicated to Discus