“Shark” for these Asian fish is a misnomer. They’re named such because of their shape, but the reality is these are catfish. They’re large catfish, for that matter, and definitely not for everyone. They require a huge fish tank – a minimum of 300-gallon tank size for adults.

So, if you’ve got a pond or massive aquarium you’re ready to house some gorgeous and intriguing fish in you, you’ve come to the right place.

Unlike many catfish, these are active fish during the daytime, moving in schools for a lot of intriguing behavior. They’re fun to watch for kids and adults alike.

If you’re ready to consider some intriguing large fish, you’ll find them rewarding and unique. So, let’s take a look to see if they’re the right fish for your home aquarium or pond.

Quick Intro to Iridescent Sharks

Family: Pangasiidae
Scientific Name: Pangasianodon hypophthalmus
Other Names: Iridescent catfish, Sutchi catfish, Siamese shark
Care Level: Advanced

Natural Habitat, Identification, and Where to Buy

The iridescent shark is native to Mekong River and Chao Phraya regions in Asia (which runs through multiple countries, including China, Myanmar, Laos, Thailand, Cambodia, and Vietnam). The region is exceptionally diverse, though the fish primarily come from Thailand, in deep rivers. In these deep rivers, large groups of adults form, where they stay towards the middle of the water column for their mealtimes.

The iridescent shark shares a family with the Mekong Giant Catfish, one of the largest freshwater fish in the world. So, not surprisingly, this fish can get rather large – up to four feet in length. They start off small, though, so don’t be deceived. These guys need a large tank for a healthy life.

The primary challenge with these fish is not the care but rather the size of their home. They need 100-gallon tank for juveniles but 300+ gallons for adults for full, healthy grow. Most folks can’t home such a larger aquarium, so they aren’t typically a great choice for most aquarists.

However, for those who are able to keep them, the bright, iridescent colors make them a colorful contribution for the tank. They’re hardy and like to clean up the tank by eating practically anything they find.

They have shiny, iridescent skin with two black stripes on and below their lateral lines. This line is a sensory organ through which they sense water changes. As they age, though, they become gray all over, and have long whisker-like barbels which help them sense their environment.

Uniquely, these catfish – unlike most species – are active during the daytime, making them additionally intriguing for fishkeepers. They’re also a migratory species, which means they swim upstream to spawn and then return to lower waters with their young.

And while these tropical freshwater fish are popular for aquarists, they are raised and fished for food, thanks to their size and affordability. They are known as swai in grocery stores.

If these fish are a good fit for your home aquarium or pond, you can purchase them online at a number of retailers.

Optimal Water Conditions for Iridescent Sharks

Water Temperature: 72-79° F
Water Flow Rate: Moderate
pH: 6.5-7.5
Water Hardness2-20 dGH

Tank Setup

Minimum Tank Size300 gallons
Optimal Tank Size500 gallons
Optimal Tank Shape: Deep, wide, and long
Recommended Filter Type: Strong filtration system

Ideally, iridescent sharks will live in a long, deep aquarium that emulates a river. They need open swimming spaces, moderate water flow rates, and natural décor that feels like “home” for them for an ideal, healthy environment.

They need the deep and wide tank specifically because they hang out in the middle region of the water. This is where they will live for the majority of their lifetime.

Iridescent sharks also need their water parameters to remain fairly steady, otherwise they become stressed, despite being hardy fish. They also need to be kept in a quiet space in your home or in ponds far from noisy highways. They get overly stressed by loud noises, consistent or inconsistent. If they get stressed they may bump into equipment and break it (thanks to their size). You’ll want to protect and pad equipment as able, especially things like heaters, to avoid them from damaging the equipment.

You’ll also need a very good filter – strong, powerful filtration. These guys are messy!

When your fish begins to outgrow a smaller tank – which is why we recommend just starting them off in a huge aquarium! – they will need about two weeks to transition to the new aquarium. Be sure to keep an eye on them and make the move before the fish have outgrown the space and become cramped. And since these are schooling fish, this is really critical for their health, or they will be too cramped very quickly.

Creating the Landscape

Iridescent sharks have sensitive barbels, which means they need to have soft, muddy beds – i.e. soft substrate. Larger rocks and driftwood as décor are good for them, but gravel should not be used as substrate. Instead, go with soft sand or substrate soil (specialized soil that won’t become actual mud).

They need an environment that resembles their native rivers. But you should be aware that these guys eat everything, including and especially plants. So, if you want a planted tank, it’s highly recommended that you keep fast-growing plants like hornwort or anacharis in their aquariums.

As you add décor, keep their swimming space in mind. Don’t overcrowd them, keep the central region clear, and avoid sharp edges.

Best Plants: Sword, Hornwort, Anacharis, Amazon Frogbit, Java Moss, Water Wisteria, Water Lettuce

Best Lighting: ModerateBest Decorations: Soft substrate, limited driftwood, larger rocksDecorations to Avoid: Decorate lightly and avoid sharp or jagged edges on stones or driftwood

Physiological Considerations for Iridescent Sharks

Size: up to 4 feet
Lifespanup to 20 years
Temperament:Peaceful fish
Preferred Tank Region: Middle
Scale Thickness: No scales
Gill Considerations:Nothing of note
Swimbladder Considerations: These fish, like most freshwater tropical fish, are susceptible to swim bladder conditions. They must have clean aquariums, detritus should be removed (overfeeding is a problem, even for them!), and care should be used to care for them.
Fin Shape Considerations: Nothing of note

These catfish can live up to 20 years, so when you bring them home, you’re in for the long haul. You really need to understand their growth rate and lifespan to be able to best care for them. The right environment can hugely impact their quality of life as well as enable them to live longer than if they’re in a tighter, smaller space or in a tank within which the parameters aren’t kept steady.

These are some of the more interesting looking and behaving catfish. Unlike many species, they’re shiny and colorful, and, of course, have those unique shark-like looks which have given them their common name. Their skin does darken as they age, into a solid dark gray shade. This sometimes leads to misidentification when they’re older, though.

They have large almost buggy eyes, which, as they age, they “grow into.”

Iridescent sharks also come in albino, which can also be available widely among fishkeeping hobbyists. They may be difficult to find, but a little patience will open some doors. They are shaped just like their non-albino counterparts, but they’re all white and have red eyes.

Most iridescent sharks grow to between three and four feet in length by the time they reach full maturity. This large size is one of the main reasons these are not recommended for newbie hobbyists.

Note: These fish have poor eyesight and use their “whiskers” to see their way around.


Despite their size and ever-rolling hunger, these fish tend to be on the timid side and get scared easily. When they do get scared, they bump into things, often hitting their heads on décor items in the aquarium or the glass walls of the tank. It’s imperative to keep them someplace quiet to help avoid this problem.

They have been known to crack the glass or jump out of their aquariums when they become scared, so it’s important to reduce their stress and keep a cover on the aquarium.

They also tend to get harassed by more aggressive fish species. They need to be kept with larger peaceful species to avoid this harassment and to avoid them from eating smaller species. They do eat practically anything, so despite being reasonably peaceful, they will nosh on other fish.

Juveniles school together, though adults gradually separate from each other.

There are a number of fish they do well with, though some they definitely should not be kept with, like tetras, danios, and barbs. They also should be housed with crustaceans, as they will become dinner for the iridescents as well.

If the fish you add together with your iridescent sharks start becoming aggressive with them, they should be separated or your sharks will become ill from the stress.

You can keep iridescent sharks together, with up to five them in one large tank. The key is making sure they are in large enough tanks – 300 gallons for a single fish, 500+ for more. They should not be kept alone. In fact, ideally a minimum of four should be housed together.

If you’re looking for more than just iridescent sharks in your aquarium or pond, consider these species, which have been known to do well as iridescent shark tank mates:

Gender, Breeding, and Reproductive Considerations

To tell the difference between males and females, you’re going to be looking at their body sizes. Females tend to be larger and “plumper” than males, meaning they have wider, less streamlined bodies.

Unfortunately, breeding iridescent sharks (unlike Bala sharks) at home is almost impossible. They need huge ponds – and by huge, I mean at least a few thousand gallons. This would emulate the natural environment for spawning in Southeast Asia. This gives them the room they require for mating.

Migration is one aspect of the mating practices of the fish, which is impossible to reproduce at home. In fact, being able to spawn them in captivity is virtually impossible for breeders as well, which is why both swai (food form of iridescent sharks) and the juveniles of this species are “wild caught.”

Nutritional Needs

Iridescent sharks are omnivores who are happy to eat anything they can get ahold of. When they are juveniles, these fish tends to eat food that is meat-based and alive.

When this fish becomes an adult, they become more vegetarian, and some will even lose their teeth. They share this behavior with other fish like Pacu.

The fact Iridescent sharks are not picky eaters (similar to Roseline Sharks) makes keeping them in tanks much easier. While all fish require a balanced diet, the fact that this fish is happy to eat a variety of pellet, flake, live, dry, and frozen foods means that you can experiment and find what works best for both you and the fish.

The easiest way to establish a balanced diet is by feeding this species quality flake food around to three times a day. It is important to not overfeed them. Make sure to give them enough food but only the amount that they can eat within five minutes.

Every two or three days you can substitute live or frozen brine shrimp or bloodworms instead of the flakes. This will help to ensure that the fish are getting the proteins they need from a variety of sources.

To further supplement their food, you can always feed them live food. Crickets, worms, and feeder fish are all great options that this species will be happy to eat. It gives nutrition and will excite your fish because it brings their natural hunting instincts.

When using feeder fish it is important to buy them from the local stores and then quarantine them for several days. This will give you a chance to observe the fish and make sure they are healthy enough to be introduced to the main tank and eaten.

  • Crickets
  • Feeder fish
  • Bloodworms
  • Brine shrimp
  • Worms
Best Sustenance Food Type: Quality flakes or pellets
Additional Food For Optimal Health:Live or frozen worms, brine shrimp, and bloodworms
Special Foods and Considerations for Best Color and Growth:Live worms, brine shrimp, feeder fish, and bloodworms
When and How Often to Feed Fish Based on Life Cycle:Two to three times a day, giving it five minutes to eat the food you feed it.

Common Diseases and How to Avoid and Treat Them

The key to ensuring your fish are both healthy and happy, they need their water to be clean. This is complicated by Iridescent catfish being a messy fish that needs a strong filter.

One way to help your filtration system cope with the mess this fish species makes is by changing at least a quarter of your tank’s water every week. While this may be time-consuming it is an investment in both your tank and fish’s health. Conducting the water changes themselves require being slow and careful. Otherwise, you can harm your fish by causing them stress.

This fish does not have scales, and this means it has a higher chance of contracting issues like Ich and skin fungus. The fish will begin to develop white dots all over its body and it will actively try to scratch the painful areas by swimming against rocks. Most of the medications available for these diseases will instruct you to use half dosage for fish that lack scales.

It is important to not only treat the symptoms your fish are experiencing but it is important to also fix the reason this fish is getting sick. Most often this fish species will get sick because of having poor water quality in its tank.

This fish does not have any species-specific diseases to watch for.

Best Antibiotics: Coppersafe, Quick-CureIch-Ease
Treatments to Avoid:Use caution with using antibiotics because they can destroy certain filtration systems.
Food Recommendations When Sick:Fresh foods with high nutritional value
Hospital Tank or Isolation Withing the Community Tank:If any of these fish become ill, they should be isolated in a hospital tank

3 Facts About Iridescent Sharks

  1. Iridescent sharks are not sharks at all, but part of the catfish family. They are called sharks, however, because of their similar body shape and a distinctive dorsal fin that makes them resemble the ocean-dwelling namesake.
  2. These catfish are commonly available in grocery stores as food, under the name Swai.
  3. Iridescent sharks are similar to American catfish species.

About The Author

Leave a Comment

Your email address will not be published. Required fields are marked *