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

Kryptopterus vitreolus is a small, see-through catfish from the rivers of peninsular and southeastern Thailand. Its name was a long time coming: for roughly eighty years the aquarium glass catfish was misidentified, first as the larger K. bicirrhis and later as K. minor, until Ng and Kottelat formally described it as K. vitreolus in 2013. The genus name means hidden fin, a nod to the tiny dorsal fin, and the species name points to its glassy look. The transparency is striking enough that the internal organs and backbone show through, and the heart can be watched beating with a hand lens. The body is clear because the fish has no scales, like other catfish in its family, and has lost most of the pigment cells that would otherwise colour or reflect light; a recent genome study tied the effect to that pigment loss and to a layered, plywood-like arrangement of collagen in the skin that lets light pass through the muscle. In the right light the body throws an iridescent shimmer, and a sick or dying fish turns milky white. It is a small species, usually around 6.5 cm and reaching about 8 cm.

Breeding

Home breeding is rare and unreliable. A few keepers report spawning after a large, cooler water change meant to mimic the rainy season, but no consistent method has taken hold in the hobby, and the transparent body makes the sexes hard to tell apart, with gravid females looking only slightly fuller. Commercial farms in Southeast Asia do breed the fish using hormone induction, which is how some farmed stock reaches the trade, but most glass catfish on sale are still wild-caught in Thailand. Keepers who hold large groups for years often never see any spawning at all.

Common problems

Water quality is the make-or-break factor. Glass catfish are among the quickest fish to react to rising ammonia, nitrite, or nitrate, and a stressed or sick fish loses its transparency, turning milky or blotchy white. That colour change is a handy early warning, though by the time it shows the trouble is usually well along, so stable water and steady maintenance matter. New fish often arrive with ich; raising the temperature is safer than dosing, since the species reacts badly to several common ich medications and does not tolerate salt. The other silent risk is starvation. Because they hover quietly and never beg, it is easy to assume they are eating when they are not, so watch for thinning behind the head and a shrinking organ cluster. Wild-caught fish can also carry internal parasites that cause the same slow wasting.

Bioload

Further reading

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