Koi Angelfish (Pterophyllum scalare)

Koi Angelfish take their name from an obvious comparison: the orange, black, and white patterning that makes koi distinctive in a pond shows up here in the flattened, sail-finned body of Pterophyllum scalare. The pattern comes from marbling genetics, which means the coloring is more variable than a solid strain — the ratio of orange to white to black shifts as the fish grows and the marbling gene continues doing its thing. A juvenile that's mostly white and orange may develop significant black by adult size, and vice versa.

In a planted tank with a light substrate, koi angels bring a visual warmth that darker and standard silver strains don't — they read as colorful without competing with the flora the way a neon or rainbow species might. A small group of three to five in a 55+ gallon planted setup tends to establish loose schooling behavior in their first few months before pairing off, which gives you a window into both their schooling and their cichlid sides.

Like all angelfish, a bonded pair will claim territory and defend it seriously. Other angelfish in too small a space will be driven away — adequate tank size and visual structure (tall plants, driftwood) lets multiple pairs coexist without constant conflict.

Scientific name: Pterophyllum scalare (koi/orange marble strain)
Origin: Amazon River basin, South America
Water parameters: Temp 76–86°F · pH 6.0–7.5 · Soft to moderately hard water
Tank requirements: 30 gal minimum; tall tank preferred
Diet: Omnivore — flake, pellet, frozen bloodworms and brine shrimp
Compatibility: Peaceful community when young; semi-territorial once paired
Husbandry note: The koi pattern tends to shift and intensify over the first year as the fish matures. Buy for the adult look you're hoping for, understanding it won't be there on day one.