Pterophyllum scalare

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Pterophyllum scalare, also called Koi Marble, is a captive-bred variety of the common angelfish, a popular South American cichlid known for its diamond-shaped body and tall fins. This form usually shows a silver or cream base with irregular black marbling and sometimes orange areas on the head and back. Very common in the aquarium trade, it retains the species’ basic requirements: warm, soft to slightly acidic water, a tall aquarium, and a varied diet. Its behavior becomes more territorial when pairs form and during spawning. Good structure and stable water are central to long-term success with this fish.

General species description

Pterophyllum scalare belongs to the angelfish group, cichlids with laterally compressed bodies and elongated vertical fins. The Koi Marble variety is an ornamental strain of Pterophyllum scalare, not a separate species. Young fish are commonly kept in groups because adults gradually establish a hierarchy and form pairs. Despite its elegant appearance, the angelfish remains a cichlid: it may defend an area, especially during breeding, and can eat small fish that fit in its mouth. A tall aquarium arranged with plants, roots, and open swimming areas supports more natural behavior. The Koi Marble form is **very common** among captive-bred angelfish.

Geographic origin and biotope

Reference countries: Brazil, Peru, Colombia, and other areas of the Amazon basin. The species inhabits quiet or moderately slow waters in floodplains, side channels, and seasonally flooded forest habitats. It is commonly associated with roots, submerged branches, and dense vegetation, where its vertical body helps it move between stems and obstacles. The water is often soft, warm, and slightly acidic, with light filtered by the forest canopy. The bottom usually consists of sand, silt, leaves, and plant debris. In an aquarium, gentle to moderate filtration, broad-leaved plants, and vertical cover reproduce this setting better than a highly mineralized, strongly turbulent layout.

Precise location and local name

The angelfish is associated with the Amazon basin, where populations occupy different tributaries and floodplain habitats. The most widely used local name in Brazil is acará-bandeira, referring to the long fins that resemble a flag or banner. In the international aquarium trade, the form described here is usually sold as Koi Marble or Koi angelfish. These commercial names describe a color pattern, while the scientific name remains Pterophyllum scalare. Aquarium strains are generally produced through several generations of captive breeding, and individuals may show considerable variation in their markings.

Appearance and physical characteristics

Pterophyllum scalare has a tall, laterally compressed body supported by long dorsal and anal fins, giving it a total height of approximately 25 cm in large adults. The Koi Marble pattern usually combines white, silver, irregular black areas, and orange shades, with intensity varying according to the strain and the fish’s condition. The pelvic fins are threadlike, while the pectoral fins are transparent. Dark bars may be more or less visible depending on age and lighting. Body length can reach roughly 15 cm in large adults. An aquarium that is too shallow restricts movement and increases the risk of damaged fins.

General diet

The angelfish is an omnivore with a carnivorous tendency and readily accepts commercial foods, but it benefits from a varied menu. Use quality cichlid pellets or flakes as a staple, supplemented with frozen or live foods such as brine shrimp, bloodworms, and daphnia. Young fish should receive small frequent meals, while adults can be fed once or twice daily depending on portion size. Excessively rich or heavy feeding encourages obesity and water pollution. Very small tank mates may be viewed as food, so adult angelfish should not be combined with tiny fish. **Dietary variety** and careful portion control are essential.

Essential data

• Native river: Amazon River
• Local name: Acará-bandeira
• Origin of the scientific name: The name describes a fish with remarkable fins and a distinctive body shape.
• Etymology of the full name: Pterophyllum means “fin-leaf”; scalare means “ladder-like” or “stepped.”
• Common/vernacular names: Freshwater angelfish, angelfish, Koi Marble
• Family: Cichlidae
• Subfamily: Cichlinae
• Name pronunciation: ter-oh-FIL-um ska-LA-reh
• Discovery: Johann Jakob Heckel, 1840
• Maximum adult size: About 15 cm body length; up to 25 cm total height
• Water temperature and pH: 24 to 30 °C; pH 6.0 to 7.5
• Watercourse appearance and surrounding vegetation: Quiet water with roots, branches, leaf litter, and flooded-forest vegetation
• Typical tank mates: Paracheirodon axelrodi, Corydoras agassizi, Ancistrus cirrhosus
• Temperament and behavior: Peaceful to territorial; lives in groups when young, then forms pairs and defends a spawning territory
• Water depth: Shallow to medium-depth areas of quiet channels and flooded forests
• Sexual dimorphism: Difficult to identify outside breeding; the genital papilla is the best clue in adults ready to spawn
• Bottom structure and flow: Sand, silt, leaves, and plant debris; low to moderate flow

In your aquarium

To succeed with Pterophyllum scalare, provide a tall, mature, well-covered aquarium with warm, clean, and stable water. Keeping young fish in a group can work when space is adequate, but tensions should be monitored as pairs develop. Hardy plants, roots, and open areas provide both shelter and territories. Choose tank mates large enough not to be swallowed and avoid excessively boisterous species. A varied diet, regular water changes, and moderate flow support healthy growth and help preserve the long fins. Aquarium height and parameter stability are the two main priorities.