Glass Catfish and Angelfish: Why They Don’t Mix (And What to Do Instead)

ByThe Answerlode Editorial Team

Glass Catfish and Angelfish: A Difficult Pairing

Glass catfish (Kryptopterus minor) and angelfish look like they should work together in a planted community tank. Both are graceful, peaceful-looking fish that appeal to the same aquarist. In reality, their needs diverge so sharply that keeping them together usually means both suffer.

Why Tank Size Is the First Problem

A 90×30×30 cm tank holds roughly 81 liters (21 gallons). This is too small for either group properly. Angelfish need height—they grow taller than they do long—and a proper setup for a group requires a 55-gallon minimum. Glass catfish need length for midwater swimming space and stability, plus the group dynamics change completely if they don’t have room to spread out.

Trying to cram both into a single undersized tank forces compromise on both fronts. The angelfish stay stunted or turn aggressive. The glass catfish become too stressed to feed.

Glass Catfish: Social Creatures That Need Their Own Space

Glass catfish are obligate schoolers. They must be kept in groups of at least 6–8 to feel secure enough to feed and behave normally. Without that security, they’ll hide, stop eating, and gradually fade. A single glass catfish or a pair will rarely thrive; they need the full group dynamic.

They are also extremely sensitive to water quality, especially nitrate buildup. They prefer soft, slightly acidic water (pH around 6.5, GH below 10) and subdued lighting. Their barbels are delicate and prone to infection if the tank has sharp décor or rough substrate.

Best companions for glass catfish are other small, peaceful fish: tetras, rasboras, dwarf gourami, and small shrimp. These species occupy different water zones and don’t compete aggressively for food.

Angelfish: Aggressive Eaters and Territorial Fish

Freshwater angelfish are deceptively aggressive. They are rapid, dominant eaters that will chase smaller fish away from food and can harass or nip delicate fish like glass catfish. They also have strict social hierarchies within their own species.

The key rule with angelfish groups is never keep two or three together. Keep either one, a bonded pair, or five or more. Two or three leads to one fish bullying the rest. A group of five gives enough spread-out space that aggression is distributed rather than concentrated on one victim.

Angelfish also grow larger than glass catfish and can reach up to 6 inches in height. As they mature, they become increasingly territorial, especially if breeding pairs form. A 55-gallon tank is the practical minimum for a small group; anything smaller limits your options or forces removals later.

Why They Conflict in Practice

The incompatibilities are structural, not just theoretical:

  • Angelfish are fast, aggressive eaters. Glass catfish are slow, picky eaters. Angelfish outcompete them at feeding time, leaving the catfish undernourished.
  • Angelfish grow large and can view smaller fish as food or competition. Glass catfish are delicate and don’t defend themselves.
  • Angelfish need the vertical height of a tall tank. Glass catfish need horizontal swimming space and stable conditions in a larger footprint.
  • If you crowd the tank to fit both, the glass catfish become too stressed to engage in normal behavior, and the angelfish lack the height they need for healthy swimming.

What to Do Instead

Choose one or the other based on your tank size. A 90×30×30 setup is borderline for a pair of angelfish if well-planted and carefully stocked. It is too small for glass catfish, which need at least 120 liters for a proper group of 6.

If you want glass catfish, build a planted community around small, peaceful fish—tetras, rasboras, small hatchetfish, shrimp, and dwarf corydoras. Skip the angelfish.

If you want angelfish, stock with mid-sized peaceful fish that don’t overlap in feeding style or water use: larger tetras, peaceful cichlids like rams, corydoras, or bristlenose plecos. Leave out fish that require dense groups or are easily bullied.

The error is not in keeping either fish, but in forcing them into the same system. Aquariums work best when you choose fish that genuinely fit together.

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