Freshwater Angelfish

Freshwater angelfish（圖片來源：mendel，採用 CC BY-SA 1.0 授權）

The freshwater angelfish (Pterophyllum scalare) belongs to the family Cichlidae and is among the most popular freshwater ornamental fishes in the aquarium trade. This species originates from the Amazon Basin of South America and is widely distributed across several countries, including Peru, Colombia, and Brazil. It occurs in major tributaries such as the Ucayali River and the Solimões River, as well as in river systems found in Guyana and French Guiana. In these regions, angelfish typically inhabit river margins, swamps, and seasonally flooded forests formed during the rainy season. They prefer slow-moving waters densely covered with vegetation, often occupying areas where floating plants, submerged wood, and tangled roots create structurally complex habitats. Such environments provide shelter while also supporting feeding and reproduction.

In the wild, angelfish spend most of their time in the middle layers of the water column. Their bodies are laterally compressed and vertically tall, with elongated dorsal and anal fins forming an elegant triangular silhouette that allows them to maneuver efficiently among aquatic plants. Wild individuals usually display a silvery body coloration with several vertical black stripes. This pattern offers effective camouflage in habitats where sunlight filtering through vegetation creates a mosaic of light and shadow. Through decades of selective breeding in captivity, however, numerous ornamental varieties have been developed. These include gold, albino, zebra, leopard-patterned, and long-fin forms, among many others.

Behaviorally, angelfish are social fish and tend to remain calmer when kept in groups of at least three to five individuals. At the same time, they possess a degree of territorial behavior. During the breeding season in particular, adult pairs will actively drive away other fish that approach their chosen spawning site. This semi-aggressive temperament means that angelfish should not be housed with overly aggressive species or with very small fish that may be harassed or eaten. When maintained under stable water conditions and proper care, angelfish commonly live for 7 to 10 years and may survive even longer.

Freshwater angelfish（圖片來源：Citron，採用 CC BY-SA 3.0 授權）

Housing Requirements in Captivity

Maintaining healthy angelfish in captivity requires recreating environmental conditions similar to those of their natural habitat. Adult angelfish can exceed 15 cm in body length and possess a body height much greater than that of many common aquarium fish. Consequently, they require aquariums that provide sufficient vertical space. A tank of at least about 200 liters is generally recommended, with a height of no less than 45 cm so the fish can fully extend their long fins. If a group of around six individuals is to be kept, an even larger aquarium is advisable to reduce crowding and minimize stress or territorial conflict.

Angelfish prefer slightly acidic to neutral soft water. The ideal pH range lies between 6.0 and 7.0, with water hardness maintained between 3 and 10 dGH. Water temperature should typically be kept between 26 and 29°C. These parameters resemble those of many Amazonian tributaries and are important for maintaining immune health as well as stimulating breeding behavior. Angelfish are sensitive to sudden changes in water chemistry, making regular water changes essential. Replacing approximately 20% to 30% of the aquarium water each week helps maintain stability, and nitrate concentrations should be kept below 50 mg/L to prevent chronic toxicity and reduced immune function.

Aquarium decoration should primarily include aquatic plants, driftwood, and large root structures. These features provide natural hiding places and can also serve as spawning substrates. Floating plants help diffuse strong lighting and create a dim environment similar to that found in their native habitat, which helps the fish feel more secure. The substrate can consist of fine sand or smooth small gravel to prevent injury to the fish. Because angelfish swim gracefully with extended fins, water movement should remain gentle. Strong currents can interfere with normal swimming and may lead to excessive energy expenditure.

Feeding Conditions

In their natural environment, angelfish are omnivorous fish with a strong carnivorous tendency. They feed on small fish, shrimp, other crustaceans, aquatic insects, and insect larvae, and they occasionally capture insects that fall onto the water surface. Under captive conditions, angelfish readily accept a wide variety of foods and are generally not selective feeders. High-quality flake or pellet foods can serve as the foundation of their diet to ensure balanced nutrition. It is also beneficial to supplement their diet regularly with live foods such as brine shrimp, bloodworms, or black soldier fly larvae. These protein-rich foods promote growth, enhance coloration, and support reproductive vitality.

To avoid nutritional imbalance, feeding should emphasize dietary diversity. Small amounts of plant-based foods, such as mashed spinach or peeled boiled peas, may occasionally be offered to assist intestinal function. Feeding should occur in small portions, typically once or twice per day, with an amount that the fish can consume within two to three minutes. This approach prevents uneaten food from accumulating and degrading water quality. If breeding is desired, increasing the proportion of protein-rich foods prior to the breeding period can help improve physical condition and egg maturation.

Breeding Conditions

The reproductive behavior of angelfish is particularly interesting. When a compatible pair forms, the two fish will jointly clean a smooth surface chosen as a spawning site. Suitable substrates include broad leaves of aquatic plants, pieces of driftwood, or flat stones placed within the aquarium. The female deposits rows of translucent eggs across the surface, while the male follows immediately behind to fertilize them. This spawning process may last several hours, and the total number of eggs can reach several hundred or even over a thousand.

Parental fish normally guard the eggs closely and fan them gently with their pectoral fins to maintain water circulation and prevent fungal growth. However, many angelfish that have been bred in captivity for generations may lose their natural egg-guarding instincts and occasionally consume their own eggs. For aquarists wishing to increase survival rates, a common practice is to transfer the substrate containing the eggs into a separate hatching tank. At a temperature of around 27°C, fertilized eggs usually hatch within two to three days. Newly hatched larvae remain attached to the substrate while absorbing nutrients from their yolk sacs. After an additional three to four days they become free-swimming fry.

At this stage extremely small foods must be provided. Suitable options include infusoria, liquid fry food, or newly hatched brine shrimp nauplii. As the fry grow larger, their diet can gradually transition to powdered foods or finely crushed flakes. One challenge in breeding angelfish lies in the difficulty of distinguishing males from females. For this reason, aquarists are often advised to raise a group of juveniles together and allow natural pair formation. Because angelfish typically form long-term monogamous pairs, once a pair successfully breeds it is best to house them in a separate aquarium to reduce conflict with other fish.

Preventing Invasive Spread

Angelfish are native to the Amazon Basin but are widely distributed through the global aquarium trade due to their popularity. If released or abandoned into natural waters outside their native range, angelfish possess sufficient adaptability to survive, particularly in tropical or subtropical climates. Under such conditions they may establish breeding populations and compete with native fish for resources, potentially disrupting local ecosystems.

For this reason, aquarium keepers should strictly follow the principle of never releasing or abandoning captive fish into natural environments. If an owner can no longer care for the fish or lacks adequate space, responsible alternatives include transferring them to experienced hobbyists or contacting local aquarium shops to determine whether they can accept the fish. Acting responsibly prevents long-term ecological problems and reflects respect for living organisms.

Author: Shui-Ye You