Glass Catfish (Kryptopterus vitreolus) Care | A See-Through Fish!

Thinking of setting up a new freshwater aquarium and looking for something different and eye-catching? We’ve got just the thing for you. Meet the glass catfish, a strange and ghostly shoaling catfish that’s almost entirely transparent! That’s right, you can actually see the bones and organs of this fish. Doesn’t get much cooler than that, if you ask us.

Below, find everything you need to know about glass catfish, including where they’re from, what they eat, and what kind of aquarium environment they thrive in.

Glass catfish description & natural habitat

Description

We love a good oddball fish here at FantaSEA Aquariums, and the glass catfish, also sometimes called the ghost catfish or phantom catfish, certainly fits the bill. We probably don’t have to tell you where it got its common names!

Glass catfish are transparent because not only do they lack scales—like all catfish—but they also lack pigment. The only time they turn opaque is when they’re very ill, extremely stressed, or dead, at which point they take on a milky color.

Its lack of pigment probably helps to camouflage the species; glass cats have been shown to have a preference for darkness, in which their transparency likely makes them very hard to spot.

These catfish grow to a maximum size of 3″, excluding the long, thin sensory barbels on their faces, which they use to feel their way around. Their bodies are laterally compressed (flat) and curved.

Did you know? As if they weren’t cool enough already, a glass catfish will look iridescent and almost rainbowy when the light hits it just right. Scientists have found this is due to the structure of their muscles. As a result, the colors flicker when they move.

Light diffraction by sarcomeres produces iridescence in transmission in the transparent ghost catfish

Will the real glass catfish please stand up?

Ahh, what would the aquarium hobby be without a little taxonomic confusion? There are 18 recognized species of Kryptopterus catfish as of now, of which a few have translucent bodies. The glass catfish sold in aquarium stores were long labeled K. bicirrhis, or sometimes K. minor.

In 2013, scientists published a study that revealed that the glass cats we love keeping in our tanks are actually neither of these species. Both of them are very rarely (if ever) exported, and thus not found in the aquarium trade. Based on these conclusions, they had to coin a new species, which they called K. vitreolus.

If you see fish sold as K. bicirrhis or K. minor in your local aquarium store, there’s a 99% chance they’re mislabeled! If it’s transparent, it’s K. vitreolus; the other two species have some pigment, as can be seen in these neat photographs of K. minor by German aquarium importing/exporting company Aquarium Glaser.

Natural habitat

Glass catfish are naturally found in Southeast Asia. Most sources consider them endemic only to southern Thailand, where they occur both on the western (peninsular) and eastern (Cardamom Mountains) side. Some think the species might extend even further south into Malaysia, but given all the confusion with the different species this may just be a case of mistaken identity.

These catfish prefer slow-moving waters, usually a dark brown to black in color due to tannins and sediment, although they may pop up in clear water as well. The fish themselves probably don’t care much about clarity; studies have shown they can navigate using magnetic fields if their eyes don’t cut it for navigation and to keep an eye on potential predators. Their barbels also help them feel their way around.

The IUCN considers Kryptopterus vitreolus to be a species of Least Concern, meaning it’s not currently threatened in the wild. The organization notes that although agricultural pollution, overfishing, and deforestation can be problematic, the glass catfish population seems to be fine.

This being said, the authors of the aforementioned 2013 study feel differently—because all glass catfish are wild-caught and their range is pretty limited, they’re worried the population may be under more pressure than it appears.

Glass catfish aquarium

Although they’re not large fish nor very active, glass catfish should be kept in groups (see the section on tankmates below). As such, we recommend an aquarium with a water volume of at least 30 gallons. This is suitable for around 8 cats; add 2 extra gallons for each additional fish.

We’ve found that glass catfish do best in an environment that replicates their natural habitat. You don’t have to make it a biotope tank—although we certainly encourage giving that a try!—but your fish will thank you for a calm tank with tannin-stained water, plenty of live plants, branches, and other décor. Subdued lighting and slow water flow also help.

If you do opt to make it a biotope, you’re spoiled for choice in terms of decorations. For example, try the following plants naturally found in Thailand and the surrounding countries:

• Crypt (Cryptocoryne sp.)
• Water wisteria (Hygrophila difformis)
• Java moss (Taxiphyllum barbieri)
• Java fern (Leptochilus pteropus; ideal beginner plant)
• Dwarf Rotala (Rotala rotundifolia)
• Rice paddy herb (Limnophila aromatica)
• Dwarf water lily (Nymphaea rubra; perfect to diffuse the light)
• Asian watermoss (Salvinia cucullata; floating plant)
• Bucephalandra (native to Borneo, but a big favorite for Southeast Asian tanks)

You can also add a nice layer of leaf litter; the Indian almond tree, whose leaves are ubiquitous in the aquarium hobby, is naturally found in Thailand. Or consider adding some Nypa palm fronds or seed pods for a natural look!

Always ensure your tank is fully cycled and free of nitrites and ammonia before introducing any fish, especially the relatively sensitive glass catfish. Stay on top of aquarium maintenance and weekly water changes while avoiding swings in water quality.

Tip: Like many other aquarium fish, glass catfish jump when startled. This is a defense mechanism that can help them evade predators, but it also makes it necessary to put a lid on your tank.

Tankmates

Before we go into tankmates, we’d like to remind you that this species can be found in groups containing many dozens of fish in the wild. It has evolved to rely on safety in numbers, so a solo glass catfish will feel constantly stressed and probably have a shortened lifespan.

Instead, get at least 6 of these catfish; preferably 10 or more. It’s not just better for the fish themselves, but also allows you to see them out in the open more often and observe their natural behaviors. It’s pretty neat to see them hovering motionlessly in the middle water layer, all facing the same direction—until you toss in some food and they become totally frenzied!

When choosing tankmates for your glass catfish, keep in mind that this species is calm, peaceful, and even rather timid. Although it will prey on small fish and shrimp fry, it won’t fare well when surrounded by overly active, nippy, or aggressive species.

Small schooling fish like Rasboras, small tetras, Otocinclus catfish, and Corydoras should work well, as should the larger bottom-dwelling Ancistrus catfish. Invertebrates like snails are fine too, but you should avoid smaller shrimp species (unless you want to use them as a live food source).

If you’d like to set up a biotope tank, choose inoffensive fish from Southeast Asia. Our favorite option are loaches from the genus Pangio. Why not try:

• Kuhli loach (Pangio kuhlii)
• Black kuhli loach (Pangio oblonga)
• Harlequin rasbora (Trigonostigma heteromorpha)
• Dwarf rasbora (Boraras maculatus)
• Cherry barb (Puntius titteya)

Glass catfish diet

As mentioned, glass catfish are carnivorous. They mostly eat bugs; the stomach contents of wild fish included stuff like insect larvae, terrestrial insects (beetles and flies fallen into the water and scooped up), and aquatic insects.

In the aquarium, these fish will usually take small commercial flakes or pellets just fine, but that shouldn’t be the only thing you feed them. Mix it up with various kinds of frozen and even live foods for the best results:

• Brine shrimp
• Daphnia
• Bloodworms
• Wingless fruit flies
• Mosquito larvae
• Various worms (grindal, glass, black)

If you keep your glass catfish with tankmates, you may find it’s best to feed after the tank lights go off. They’re mostly active at night, and this helps prevent them from being outcompeted by other fish. Remove any leftovers the next morning.

Did you know? Healthy, well-fed and stress-free glass catfish have been reported to live for 8 years or more.

Breeding glass catfish

As we mentioned earlier, all glass catfish available in the aquarium trade as of now are wild-caught (in the millions!). It would be great to be able to breed them on a commercial scale so the wild population isn’t affected, but only limited success has been achieved so far.

Bad luck for the home aquarist: only a handful of people seems to have managed to get their glass cats to breed so far. We found a report over at Planet Catfish, but that was an “accident” and the aquarist didn’t spot the sole surviving baby cat for weeks!

Scientists did manage to get glass catfish to breed in captivity, but they use a method known as “induced breeding”. This involves injecting the fish with hormones to stimulate egg maturation and is very common in commercial fish breeding operations. The females don’t actually scatter the eggs like they normally would. Instead, they’re extracted straight from their bodies.

Anyway, here’s what was found:

• The eggs are round, yellow, and sticky.
• At a temperature little over 77 °F, the fry hatched after 21.5 hours. Less than a day!
• Larvae hatch at about 2.8mm in length and finish their yolk sacs at 3-4 days of age.

Unfortunately, these studies from 2019 and 2020 didn’t mention what they fed their baby glass catfish. Given the larvae were around 6mm when they finished their yolk sacs, we’d assume they can handle baby brine shrimp and small species of Daphnia, so that should be worth a try.

Conclusion

Glass catfish are among the most eye-catching and unusual species you can keep in your freshwater aquarium. Aside from their timid nature requiring some special measures, they’re easy enough to keep and suitable for beginners.

Thinking of setting up an aquarium but feel you don’t have the time or expertise? That’s where we come in! Contact FantaSEA Aquariums with your ideas. Our expert team can design, set up, and maintain your dream aquarium for you. All you have to do is enjoy it!