Glass catfish, also known as ghost catfish, transparent catfish, or phantom catfish, belong to the genus Kryptopterus. Their see-through bodies, allowing a view of their bones and organs, make them a popular choice for aquarium enthusiasts. The natural transparency of Kryptopterus vitreolus has also made it popular as an experimental subject in science.
Identifying Glass Catfish Species
While the Kryptopterus genus includes multiple species, only three have clear bodies:
- Kryptopterus minor
- Kryptopterus piperatus
- Kryptopterus vitreolus
For a long time, Kryptopterus bicirrhis was often mistaken for Kryptopterus vitreolus in the pet trade. The key difference is that only the area near the head of K. bicirrhis is clear, while the body of K. vitreolus is completely transparent. Most glass catfish in the aquarium trade once labeled K. bicirrhis are likely K. vitreolus.
Appearance and Characteristics
The clear appearance of K. vitreolus and other glass catfish is due to their lack of pigmentation. Unlike other types of catfish, their skin cells don’t carry color. They also lack scales, like all catfish. When glass catfish die, they become a milky white color, indicating that maybe something the catfish does while alive produces the cells.
Like most catfish, glass catfish have barbels, the “whiskers” on their heads, used as feelers to find food. In glass catfish, they are completely clear like the rest of the body. The fins of the glass catfish are also see-through. Glass catfish have an anal fin, or a fin that runs along the underside of their body, and a forked caudal fin. Another feature that sets glass catfish apart from other types of catfish is their lack of a dorsal fin. The genus name comes from this; Kryptopterus is Greek, with ‘kryptos’ meaning hidden and ‘pterus’ meaning fin, thus "hidden fin". According to the study, the fish shows flickering iridescence throughout the transparent body.
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Size
Glass catfish size can vary widely between species. Kryptopterus vitreolus usually grows to about 3.1 inches (8 centimeters), while Kryptopterus minor reaches about 2.7 inches (6.8 centimeters) on average. Kryptopterus bicirrhis, the fish that K. vitreolus was often mistaken for, can grow much larger, an average of 5.9 inches (15 centimeters). The Ghost Glass Catfish are relatively small fish species.
Distinguishing Males and Females
It’s almost impossible to tell male and female glass catfish apart. The only difference is that males are usually slightly smaller than females.
Natural Habitat and Distribution
All species in the genus Kryptopterus are found in freshwater habitats in Southeast Asia. The exact location depends on the species.
- Kryptopterus minor is found mainly in Indonesia.
- Kryptopterus piperatus is typically found within forest rivers with a moderate current in Indonesia, especially the Alas River and Lembang River.
- Kryptopterus vitreolus is found throughout the peninsular and southeastern areas of Thailand, usually in slow-moving or standing murky water. There have been reports of sightings in Malaysia, but those are yet to be verified. It occurs in rivers that flow into the Gulf of Thailand and river basins in the Cardamom Mountains. However, due to intra-species confusion, the precise distribution range of this species requires further clarification.
While many species of catfish are bottom feeders, glass catfish often prefer to swim in the middle of the water. This is another reason they’re a popular aquarium fish, as they’re much more active than other species of catfish.
Aquarium Care
Glass catfish are relatively easy to care for, making them an excellent addition to a freshwater aquarium.
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Tank Size and Setup
Experts recommend keeping glass catfish in groups of six or more. So you’ll need an aquarium that can hold at least 30 gallons. This should be enough for about eight fish. Add 2 gallons for each additional fish. For a small group of 6-8 fish, you will need at least a 20-gallon (80 liters) tank.
Glass catfish seem to do best in environments similar to their natural habitat. Create a calm tank with tannin-stained water, lots of live plants, branches, and other décor. Subdued lighting and slow water flow also help. You can also go the extra mile and create a biotope tank by adding plants native to Southeast Asia. The tanks should have plenty of open space where they can swim freely. You’ll also want to make sure there are some plants in their aquarium as well. Replicating this in their tank will give them a sense of comfort and safety since plants are something they’re familiar with using for shelter. A soft substrate is another thing you’ll want to use when setting up a tank for glass catfish. These fish aren’t as durable as many other catfish so anything that can cut them, likely will. Lastly, you’ll want to consider water flow too. You don’t need to do anything special to give them the right amount of current, just know that they can’t have static water. Avoid high abrasiveness of the substrate with materials like sand or fine gravel to protect the delicate-bodied animals. Glass catfish are better off with low to moderate lighting. LED lights which can adjust the brightness of the light are good to use to be able to create the conditions of the natural environment and prevent the growth of algae. These fish need their water to be highly oxygenated.
Water Parameters
While glass catfish aren’t difficult to care for, they do require certain water parameters. This includes:
- Hardness level between 8 and 12 degrees of general hardness (dGH), the recommended general hardness (GH) range for these fish is 3 to 15 dGH.
- pH between 6.5 and 7.5
- Temperatures between 75 F and 80 F (24 C and 26.7 C), although they can survive in temperatures between 72 F and 82 F (22.2 C and 27.8 C)
- Nitrates should be below 20 ppm and the ammonia and nitrite should be at 0 ppm at all times.
- The water in the tank should have a medium flow to it.
It’s important that you perform regular tests to be sure everything is stable. Maintaining a stable water temperature, gentle water circulation, and peaceful water conditions in the aquarium.
Diet and Feeding
In the wild, glass catfish mostly eat very small fish or small invertebrates such as:
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- Mosquito larvae
- Tiny crustaceans, such as water fleas (Daphnia)
- Zooplankton
When keeping pets in an aquarium, you should try to imitate their wild diet as closely as possible. Daily pellet or flake food is important and will provide the basic nutrients for your fish. For added protein, you can also offer your glass catfish:
- Bloodworms
- Brine shrimp
- Grindal worms
- Tiny crustaceans such as daphnia
- Zooplankton such as moina
Glass catfish food in captivity should mimic their diet in the wild as much as possible. A strong flake or pellet food is a great place to start and it’s something you’ll be giving them every day. Some high protein sources such as bloodworms, brine shrimp, and daphnia are all great additions as well. You don’t want to feed this to your ghost catfish too often, but a few times a week should be fine. The main drawback of this feeding habit is that any food that falls to the bottom is rarely picked by them. Thus, if there is no cleaning crew (such as snails or shrimp) it can lead to ammonia, nitrite, and nitrate buildup in the tank.
Tankmates
Glass catfish normally travel in groups, called schools. As a result, they need to be around other fish. They should be in schools of six or more, preferably 10 or more. A glass catfish that’s all alone will live in a constant state of stress which can seriously impact their health and lifespan. Aim for a school of 5 or more to keep them happy and healthy.
Glass catfish are generally peaceful fish. If you’re keeping them in a tank with other fish, they need to be with species that are peaceful and not too large. Suitable companions for these little fish are other small, peaceful fish, such as tetras, rasboras, or other fish used in community tanks. Some ideal tankmates include small peaceful fish like tetras, rasboras, or other community species. Invertebrates like snails are fine too, but you should avoid smaller shrimp species (unless you want to use them as a live food source).
When choosing tankmates for your glass catfish, keep in mind that this species is calm, peaceful, and even rather timid. Small schooling fish like Rasboras, small tetras, Otocinclus catfish, and Corydoras should work well, as should the larger bottom-dwelling Ancistrus catfish. 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.
At the same time, it is important to understand that this species is a micro-predator, and it is not advisable to keep them in an aquarium with other fish that may have fry, as the catfish will prey on them. It is not recommended to keep Ghost Glass Catfish with dwarf shrimp.
Lifespan
On average, glass catfish live for about six to eight years. Their lifespan can be shortened significantly if you don’t provide them with the proper tank conditions. Healthy, well-fed and stress-free glass catfish have been reported to live for 8 years or more.
Breeding
There isn’t much information known about the life cycle or breeding practices of glass catfish. Glass catfish are very difficult to breed in captivity. 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.
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. At a temperature little over 77 °F, the fry hatched after 21.5 hours. Unfortunately, these studies from 2019 and 2020 didn’t mention what they fed their baby glass catfish.
If you are going to attempt breeding glass catfish then a basic understanding of their natural breeding patterns is essential. The main thing you’ll need to do is condition the tank to encourage the process. Some have recommended phasing in a little bit of freshwater into the tank during this period of time to replicate rainfall as well. If you successfully initiate the breeding process then you’ll witness some different interactions between the spawning pair. One of the reported behaviors is the pair getting face to face and touching each other with their barbels. If breeding is successful you’ll see them deposit their eggs in some of the available plants in their tank (leafy plants are ideal). Once they’ve hatched you’ll need to feed them protein-rich foods to help them grow.
If the female glass catfish is pregnant, she should have some kind of lump around the abdominal area. They will generally be laid so that the male fish will fertilize them on the outside. The fry hatch in about 72-96 hours. Sand them with infusoria or powdered fish food until they get to a size that they will need.