Glass catfish

Where they come from

Glass catfish (Kryptopterus vitreolus) come from Thailand, mostly slow-moving rivers and floodplain areas where the water is warm, tannin-stained, and full of plants and roots. They are not a tough, adaptable "anything goes" fish - they act a lot more relaxed once you give them cover and calm water.

Setting up their tank

The biggest thing with glass cats is making them feel safe. If they feel exposed, they will bunch up in a corner, go pale, and act like you do not exist. Give them a tank with plants, shade, and a gentle flow and they turn into confident little hovercrafts.

• Tank size: I would not do them in less than 20 gallons long, and bigger is easier. They are active schoolers once settled.
• Group size: 6 is the bare minimum. 8-12 is where you start seeing the real behavior.
• Filtration and flow: clean water, but not a washing machine. Aim for gentle-to-moderate flow with calm areas behind decor.
• Decor: plants (real or good fake), driftwood, and some dim zones. Floating plants help a lot.
• Lighting: they look best under softer light. Bright, bare tanks make them skittish.
• Substrate: anything is fine. I like darker sand or gravel because it keeps them calmer.

Water-wise, think warm and stable. Mid-70s to low-80s F is a comfortable range. They do well around neutral pH, but stability beats chasing numbers. What they do not like is dirty water or wild swings after big, sloppy water changes.

What to feed them

Glass catfish are micropredators. They love small meaty foods and they feed up in the water column, not off the bottom like a lot of people expect from a catfish.

• Staples: frozen/thawed bloodworms, brine shrimp, mysis, daphnia
• Live foods (great for getting new fish eating): baby brine shrimp, daphnia, blackworms (if you trust the source)
• Prepared foods: smaller sinking micro pellets and fine granules can work once they are settled

In my tanks they sometimes ignore flakes, especially at first. Target feeding helps: thaw frozen food, use a turkey baster or pipette, and puff it right in front of the school. Once they learn the routine, they come right out.

How they behave and who they get along with

They are peaceful, schooling fish. Most of the time they just hover in formation and gently drift in and out of plants. If you have enough of them, you will see them cruise the whole tank instead of doing the scared statue routine.

• Good tankmates: small rasboras, peaceful tetras, cherry barbs, peaceful danios, kuhli loaches, small peaceful gouramis, otos
• Use caution with: fast, pushy eaters (they can outcompete glass cats at feeding time)
• Avoid: fin nippers, aggressive cichlids, and anything big enough to fit them in its mouth

They are also jumpy during sudden changes. If you bang the lid or flip the lights on in a dark room, they can spook hard. A lid is a good idea, and I like having some floating plants to break up the light.

Breeding tips

Breeding glass catfish in home aquariums is not common. Most of what we see in the hobby is farmed or wild collected, and they do not just casually spawn in a community tank like livebearers.

If you want to take a swing at it, the usual approach is a dedicated, calm setup with heavy plants (fine-leaf plants or spawning mops), very clean warm water, and a well-fed group. Some folks try seasonal cues like slightly cooler water changes followed by warming back up, but success stories are rare and details are all over the place.

Common problems to watch for

• Hiding and stress: almost always from too small a group, too bright a tank, or not enough cover
• Not eating: common right after purchase. Offer live/frozen foods and target feed
• Skinny fish in a community tank: they get outcompeted. Watch them eat, do not assume they are getting food
• Ich after adding new fish: they are sensitive and ich spreads fast in warm tanks. Quarantine new arrivals if you can
• Ammonia/nitrite issues: they do not handle cycling mistakes well. Keep the tank mature and test if anything seems off
• Injuries from rough decor or nets: use soft nets and avoid sharp plastic plants. They are delicate

One last practical thing: their "glass" look makes every little bit of stress obvious. If they look washed out, clamp up, or start doing that tight corner huddle, take it as a real-time gauge that something in the setup or routine is bugging them.