Species profile

Mercury Discus

Symphysodon aequifasciatus var. "Mercury"

Common names: Mercury Discus

Colour varietyCichlids

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Adult size

Up to 18 cm

Typical adult length 15–18 cm.

Up to 18 cm

Countries of origin

Good fit for your tank?

Good fit for

You can keep a group of five or more in a tall, mature tank
You can do large, regular water changes
You want a calm, warm-water showpiece

Think carefully if

You are new to fishkeeping
You keep cool-water fish, or shrimp you want to protect
You cannot hold the water warm and stable

A light blue body with a yellow tint on the head, a clear tail and red eyes. It is a captive-bred form of Discus, with the same care needs: a warm, stable, very clean tank and a group of at least five.

Appearance and Identification

A light blue body with a yellow tint on the head, a clear tail and red eyes.

The pale blue and clear tail are the marks to look for. Discus with very similar genes are sold under different names, and one seller's name may not match another's, so judge a fish by its pattern, body colour, pepper (fine black speckling) and eye colour.

Sexes are hard to tell apart by eye. Mature males may be larger with a broader head, but the breeding tubes and spawning behaviour are more reliable.

Tank Requirements

Suggested filter: About 700–1,050 litres an hour
Suggested heater: About 350–525 W for this tank
Minimum tank volume: 350 litres
Minimum tank length: 150 cm
Minimum group size: 5
Recommended group size: 6
Activity level: Moderate
Flow preference: Low
Planting preference: Moderately planted
Hiding places: Yes
Lid recommended: Yes
Jumping risk: Low

Keep a group of at least five or six in a tall, mature tank with excellent filtration, calm flow, open feeding space and vertical cover. Quarantine all new fish.

Behaviour and Tankmates

A calm, shoaling cichlid that can become shy, bullied or underfed in too small a group.

Groups form a pecking order. Pairs separate to spawn and may need their own breeding tank.

Breeding pairs defend a vertical surface and the area around it. Outside breeding, aggression is mainly social ranking.

Use calm, warm-water tankmates that do not nip fins or take all the food. Small fish and shrimp may be eaten.

Check tankmates for this species

Water Parameters

Temperature: 27–31 °C
pH: 6–7.5
GH: 0–10
Stability importance: Critical

Captive-bred discus are usually kept at pH 6 to 7, and can take up to 7.5 if it stays stable. Temperature and water cleanliness must stay consistently high.

Parameter caveat

Stable water matters more than an exact number. Do not mix fish from very different water without slow acclimation.

Feeding

Diet types: Insectivore, Omnivore
Feeding frequency: Daily
Preferred foods: Quality discus pellets or granulesA good daily staple. Feed small amounts and remove what is not eaten, because leftovers foul warm water quickly.
Frozen bloodworm and brine shrimpOffer often for variety and condition.

An omnivore that does well on varied pellets and frozen foods.

Feed several small meals a day, and remove uneaten food quickly in warm water.

Breeding

Breeding type: Egg Layer, Substrate Spawner
Breeding difficulty: Difficult
Brood or egg count: Commonly 100 to 400 eggs
Incubation: 3 days
Parental care: Biparental care
Baby foods: Skin mucus from the parentsFry feed on this for about their first four weeks. Parent-raised fry survive better than fry raised without it.
Newly hatched brine shrimpAdd as the fry grow and start to swim away from the parents.

Pairs lay on vertical surfaces. Both parents guard the eggs and produce a skin mucus that feeds the fry for about their first four weeks.

Habitat and Origin

Geographic origin: Amazon Basin, Brazil, Captive Bred, Colombia, Peru, South America
Natural habitat: Blackwater, Clearwater, Floodplain, Slow River
Aquarium contexts: Breeding Aquarium, Large Freshwater Aquarium, Planted Aquarium
Audience level: Advanced

Classification

Profile type: Colour variety
Genus: Symphysodon
Family: Cichlidae
Species group: Cichlids, Discus, Fish, South American Cichlids

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Good fit for

Think carefully if

Appearance and Identification

Tank Requirements

Behaviour and Tankmates

Water Parameters

Feeding

Breeding

Habitat and Origin

Classification

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