Glass catfish

Quick facts

Adult size

8 cm

Lifespan

can live up to 8 years

Tank zone

mid

Temperament

peaceful

Difficulty

intermediate

Schooling

recommended 6+ (critical minimum 4, thrives at 8+)

Typically wild-caught

yes - acclimate slowly

Water parameters

Temperature

24–28°C

pH

6.0 to 7.5

Hardness

2 to 12 dGH

Tank requirements

Minimum volume

100 L

Minimum length

75 cm

Flow

moderate

Lighting

dim preferred

Substrate

any

Hiding spots

needed

Open swimming room

needed

Feeding

Diet: carnivore, feeds primarily at the mid.

Frozen bloodworm, frozen brine shrimp, frozen daphnia, and live food (baby brine shrimp, daphnia, mosquito larvae) are the primary diet. Dry food is accepted reluctantly; most glass catfish prefer frozen or live over flake and pellets. They don't chase food; they hover in the current and intercept particles that drift past their mouth. In still-water tanks, food sinks past them before they react. A gentle current that carries food through their schooling area is the best feeding strategy. Feed twice daily. In community tanks, targeted feeding with a pipette or turkey baster near their school helps ensure they eat. Unfed glass catfish waste away quietly without showing obvious distress until it's too late.

Compatibility

• Strictly a group fish. Glass catfish kept singly or in pairs refuse food, hide constantly, and die within weeks. Groups of 6+ transform the behavior completely: they hover in the open in a loose school, aligned in the same direction against the current.
• Peaceful to the point of being fragile in community setups. They don't compete for food, don't defend territory, and flee from conflict. Tankmates should be equally calm: small tetras, rasboras, corydoras, and shrimp. Avoid anything boisterous or aggressive.
• Mid-water hovering fish. They hold position in a current and let food drift to them rather than actively foraging. This means they need gentle to moderate flow from the filter and they occupy a different behavioral niche than most community fish.
• Sensitive to noise and vibration. Glass catfish near speakers, slamming doors, or high-traffic areas in the home startle easily and spend more time hiding.

Habitat

Native to rivers and streams in mainland Southeast Asia, primarily Thailand and the lower Mekong basin. Found in clear to slightly turbid water with moderate current, over sandy substrates with vegetation. The species (Kryptopterus vitreolus, formerly misidentified as K. bicirrhis for decades) was only correctly described in 2013, which means older references use the wrong species name. The transparency is the obvious selling point: the body is almost completely see-through, with the internal organs visible as a metallic cluster behind the head and the vertebral column visible along the length of the fish. Muscles, the swim bladder, and the digestive tract are all visible in living specimens. The transparency is structural, caused by the absence of reflective guanine crystals and pigment cells in the skin and scales. If the fish is stressed, sick, or dies, the body turns opaque milky-white. This opacity change is a reliable indicator of problems. Adult size is about 6–8 cm. Both wild-caught and commercially bred specimens are available. Wild-caught are still common in the trade.

Breeding

Rarely bred in home aquariums. Occasional reports describe spawning triggered by a large, cool water change during the rainy season analogue (dropping temperature by 3–4°C and reducing photoperiod), but consistent, repeatable breeding in captivity has not been documented in the hobby literature. Sexing is extremely difficult because the fish are transparent and sex organs are not easily distinguished externally. Gravid females may appear slightly fuller when carrying eggs. Commercial breeding reportedly occurs in Southeast Asia using hormone injection, which is how farm-bred stock reaches the trade. Most glass catfish sold in stores are wild-caught from Thailand. Attempts at home breeding remain hit-or-miss, with most keepers never observing spawning behavior despite maintaining large groups for years.

Common problems

Sensitivity to water quality is the defining care challenge. Glass catfish are among the first fish to show stress when ammonia, nitrite, or nitrate levels rise. The transparent body turns milky or develops white patches when the fish is sick or stressed, which is useful as a visual warning but usually means the problem is already advanced. They require stable, clean water with regular water changes. Ich affects newly purchased fish frequently; treat with temperature elevation (30°C) rather than chemical medication, as they're sensitive to several common ich treatments. Wasting from insufficient feeding is a silent killer. Because they hover quietly and don't beg for food, it's easy to assume they're eating when they're not. Watch for thinning behind the head and a visible reduction in the organ cluster's size. Internal parasites from wild-caught specimens cause similar wasting; treat with praziquantel or levamisole. The species does not tolerate salt treatment.

Bioload

Bioload coefficient: 2.0 (small, lean-bodied; minimal waste).

Bioload coefficients are calibrated against the neon tetra as the anchor (1.0). See the methodology page for the formula and how each value was derived.

Further reading

• How to cycle a fish tank
• Stocking ideas by tank size