Glass catfish

Water parameters

Tolerated range for this species. Aim for the middle of each band rather than the extremes.

Tank and habitat

Substrate: any.

Behavior

Plant interaction: plant safe.

Typically wild-caught; acclimate slowly.

Feeding

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.

Origin and habitat

Endemic to Thailand: coastal river basins of Peninsular Thailand draining into the Gulf of Thailand, south of the Isthmus of Kra, plus river basins in the Cardamom Mountains. Unconfirmed reports from Penang, Malaysia. The species was misidentified for over 80 years: first as K. bicirrhis (a larger, less transparent species), then as K. minor (endemic to Borneo). Correctly described as K. vitreolus by Ng and Kottelat in 2013. Known in the hobby since at least 1934. The genus name Kryptopterus means "hidden fin" (Greek kryptos + pterygio) for the reduced dorsal fin. Vitreolus is a diminutive of Latin vitreus, meaning "of glass". Among described Kryptopterus species, only two others (K. minor and K. piperatus) have clearly transparent bodies; both are absent from the aquarium trade. The transparency is because, like all catfish, they're scaleless, and this species lacks body pigment. Most organs are located near the head; with a magnifying glass you can watch the heart beating. When light strikes the fish at the right angle, it creates an iridescent rainbow shimmer. They turn milky white during illness and after death. Size about 7 cm.

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

Further reading

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