Glass catfish
Kryptopterus vitreolus
Glass catfish exhibit a transparent, elongated body with a faintly visible skeleton, and long, slender fins that enhance their delicate appearance.
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About the Glass catfish
This is the truly transparent "glass" catfish from Thailand - you can literally see the spine and organs when its happy and settled in. The big trick is keeping them in a proper group and giving them calmer, dimmer conditions; once they feel secure, they cruise around together and look unreal in the water column.
Also known as
Quick Facts
Size
6.5 cm SL
Temperament
Peaceful
Difficulty
Intermediate
Min Tank Size
30 gallons
Lifespan
6-10 years
Origin
Southeast Asia
Diet
Micro-predator (carnivore leaning) - small frozen/live foods like bloodworms, brine shrimp, daphnia; will usually take quality sinking micro pellets once settled
Water Parameters
23-27°C
5.5-7
3-12 dGH
Need a heater for this species?
This species needs 23-27°C in a 30 gallon tank. Use our heater calculator to find the right wattage.
Calculate heater sizeCare Notes
- Keep them in a real group - 6 is the bare minimum, 10+ is where they stop acting spooky and actually hang out in the open.
- They like calm, shaded tanks: dim lighting, dark substrate, plants or wood for cover, and gentle flow (a sponge filter or baffled output helps a lot).
- Aim for stable, clean freshwater around 74-80F (23-27C), pH 5.5-7.0, and soft-to-moderately hard water; they are highly sensitive to fluctuations in water quality/chemistry.
- They are midwater planktivore types - feed small stuff that drifts: frozen baby brine, daphnia, cyclops, and small pellets/micropellets once they recognize it as food.
- Feed with the lights low and spread food across the flow; otherwise the bolder fish will steal everything before the glass cats even notice it.
- Good tankmates are peaceful schooling fish and gentle bottom dwellers (rasboras, small tetras, corys); avoid fin nippers and pushy eaters like barbs, big tetras, and most cichlids.
- Watch for them turning pale, hiding nonstop, or breathing hard - that is usually stress from bright lights, too much current, or sketchy water quality, and they can crash quicker than hardier cats.
- Breeding in home tanks is rare; if you ever try, start with a big group, soft slightly acidic water, lots of plants, and expect eggs to get eaten unless you separate adults.
Compatibility
Good Tankmates
- Small, chill midwater schooling fish like rummy-nose tetras, ember tetras, or harlequin rasboras - they match the calm vibe and wont hassle the glass cats, and the entire tank appears more lively when all the fish school together.
- Corydoras (any of the peaceful ones) - they keep to the bottom, dont bully, and they make the glass cats feel safer because there's less stress in the tank.
- Kuhli loaches - super peaceful, mostly nocturnal, and they dont compete much at feeding time if you spread food around.
- Otocinclus - calm little algae crew, totally non-threatening, and they wont spook the glass cats (just make sure the tank is mature so the otos dont starve).
- Honey gourami - one of the few gouramis Ive seen that usually stays mellow, and they wont treat glass cats like targets the way the feistier gouramis sometimes do.
- Small, peaceful apistos like Apistogramma borellii - works best with lots of plants and caves so they can claim a corner and ignore everyone else (avoid spicy breeding pairs).
Avoid
- Tiger barbs and other nippy barbs - glass cats hover and startle easily, and fin-nippers will keep them pinned in hiding and stressed all the time.
- Most aggressive or territorial cichlids (convicts, jewels, big Central Americans) - theyll bully the whole midwater zone and the glass cats wont get to eat in peace.
- Bettas - its a coin flip, but Ive seen enough bettas take a personal interest in anything that glides around slowly that I just dont bother mixing them.
- Big predatory fish like larger gouramis, adult angelfish, or anything that can fit a glass catfish in its mouth - if theres even a chance, it eventually happens.
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.
If yours are glued to one back corner all day, the fix is usually: bigger group, more cover, and turning the lights down a notch.
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.
They are pretty sensitive after shipping. Quarantine if you can, and do not dump them into a brand new tank. A mature tank makes your life way easier with this species.
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.
Feed smaller portions more often for the first couple weeks. New glass cats can be shy eaters, and you do not want food rotting while they build confidence.
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.
If you ever do see eggs, assume they will get eaten. You would want to pull adults or move eggs to a separate rearing container with gentle aeration.
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
Do not medicate blindly with strong doses, especially with copper-heavy meds. If you have to treat, look up whether the product is catfish-safe and consider starting at a reduced dose.
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.
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