Iridescent Shark Care Guide: Tank Mates, Tank Size, Growth Rate

The word ‘shark’ on its own is enough to send chills down peoples’ spine. The fear for this large predatory fish is somewhat lost on the iridescent shark, just like the red tail sharks.

Iridescent sharks, also known as the siamese shark or sutchi catfish, are a species of catfish native to Southeast Asia and Thailand.

In the aquarium, they provide a lot of schooling activity. They are favored for their behavior and appearance.

If you are thinking about keeping this fish, you should read our complete care guide below to learn everything you need to know.

Care Level:Advanced
Color Form:Silver with Darker Dorsal Side
Lifespan:Up to 20 Years
Size:Up to Four Foot
Minimum Tank Size:300 Gallons
Tank Set-Up:Pond or Huge Aquarium
Compatibility:Other Larger Fish


Iridescent Shark

Scientifically they are known as Pangasianodon hypophthalmus, and they share a family with the Mekong Giant Catfish (one of the largest freshwater fish in the world).

As a matured adult the iridescent shark can grow up to four foot. Many people will buy them as small juveniles and not realize how big they can get.

The biggest challenge when keeping these fish is having the right size aquarium. While a 100 gallon for juveniles will be ok, 300 gallons will be needed as they begin to grow.

Their bright flashy colors have made them popular in the aquarium trade. They are hardy fish and eat a wide variety of food. Like most catfish or even goldfish, these sharks will eat anything they can find and as often as possible; this is what allows them to grow to such enormous sizes.

Typical Behavior

Iridescent sharks are fairly timid and can be easily scared. When this happens, they may hit their head on the glass or decor.

You can help keep them calm by placing the tank in a fairly quiet area, somewhere they aren’t likely to be scared by loud noises or people passing by the tank.

They are also likely to get harassed from more aggressive fish. Therefore, keeping them with large peaceful fish is important. There is an emphasis on large because any fish that can fit into the shark’s mouth will likely become food.

As juveniles they school together and separate as adults. This schooling, combined with the flashing skin, is yet another reason why they were brought into the aquarium trade.


Pangasianodon hypophthalmus

As the name states, these fish are iridescent. They have shiny skin on their sides as juveniles. They also have two black stripes on and below their lateral line. This line is a sensory organ that is filled with nervous tissue used to detect changes in the water.

Once they reach adulthood however, they start to become uniformly gray. Another trait for adults you must have noticed by now is their size.

Females are usually larger and ‘plumper’ than males.

One unique thing about these fish is the fact they are “naked catfish”, meaning they do not have bony plates over their body. They do however have skin and choose to live in the middle of the water column.

They have long, whisker like barbels, that help them to sense the environment.

There are a lot of sensory organs in fish like this and the reason stems from the water quality they are used to in the wild. Waters may be murky so they are not able to use their eyes all the time.

Habitat and Aquarium Setup

Iridescent Catfish

Native to Thailand, these fish thrive in deep rivers. These deep waters allow for large groups of adults to form. They stay in the middle of the water column and search for food.

They come from an incredibly diverse area (the Mekong River) which has direct effects on both fish and human populations.

The barbels on their head help them to search for food. This adaptation allows them to feel their way around in low visibility and water where a lot of sediment or low light is present.

Speaking of light, these fish are not like most catfish who are active at night; they are active during the day.

They are also migratory fish. During rainy season, they swim upstream to spawn, only to return to lower waters to rear their young.

Tank Conditions

Using this information, a fish tank that is modeled on a river is best for these fish. This means having an open swimming space with rocks and driftwood around the floor of the tank.

The important part of the tank setup is the open middle water column. This is where your fish will spend most of their time and they will need a lot of room.

To keep these fish stress free, make sure the water parameters do not fluctuate so much. As with most fish, they do not respond well to changes in these conditions even though they are hardy.

Iridescent Catfish require the following conditions:

  • Temperature: 72-79°F
  • pH: 6.5-7.5
  • Hardness: 2-20 dGH
  • Water Movement: Moderate
  • Light Levels: Moderate

These fish have sensitive barbels so a soft substrate is needed. This will also replicate the river conditions they are used to in the wild, which usually have a soft muddy bed.

It is important to think about this fish’s large size and their nature. When they get scared, they can bash into equipment such as heaters and break them. To stop this, make sure you keep the tank in a quiet area of your home.

Also consider hiding heaters where they cannot be broken, either using an external in-line or an under gravel heater.

You’ll need a powerful filter to help keep the tank water clean because these fish are very messy!

Plants can be eaten by these fish and should generally be avoided unless you’re happy for them to be eaten. If you choose to include plants, choose fast growing species such as hornwort and anacharis.

What Size Aquarium Do Iridescent Sharks Need?

A juveniles iridescent shark will need at least a 100 gallon aquarium. As adults they will need a 300 gallon tank.

As juveniles they will thrive within groups of around 4 or 5. This schooling will allow them to swim in the water column with less fear. After 300 gallons for the first fish, you should allow another 150 gallons for each iridescent shark that you add.

Tank Mates for Iridescent Sharks

Tank Mates for Iridescent Shark

The biggest thing to remember when putting these fish with others is their size. Any fish that can fit in their mouth are likely to end up being enjoyed as a meal.

This means fish like Tetras, Danios and Barbs are not good companions.

The good things are that these fish can be housed with lots of large peaceful fish such as:

  • Plecostomus
  • Synodontis catfish
  • Pearsei
  • Silver dollars
  • Kissing gourami
  • Leptobotia elongata loach
  • Oscar
  • Texas cichlid
  • Salvin’s cichlid
  • Bichir
  • Fire eel

Any crustaceans will not do well with these fish and will likely end up being dinner.

As always, when adding more aggressive fish make sure to watch them interact. You never want to have your fish bullying one another.

If you ever have problems, then remove the aggressor from the tank. Most stores will take fish back for credit. This will keep your tank healthy as well as make sure you are not just wasting money trying new fish out.

Keeping Iridescent Sharks Together

Juveniles work best in groups and should be kept together. Having around 4 or 5 will make sure they thrive in your tank.

What To Feed Iridescent Sharks

The iridescent shark is an omnivore; they eat anything they can find.

As juveniles, they tend to eat more and more live and meaty foods; however as adults they tend to become more vegetarian and even lose their teeth. This behavior is also shared in other fish like the Pacu.

In the aquarium, this means your job is a bit easier. They require a balanced diet but will eat a variety of live, frozen, or pellet/flake foods.

To make sure their diet is balanced, feed your iridescent catfish high quality flakes two or three times a day. Make sure to not overfeed them by only giving them enough food so that they eat it all within 5 or so minutes.

Then feed them live or frozen Bloodworms or Brine shrimp. Do this instead of the flakes every 2 or 3 days. This will help to give them the protein they need from a different source.

Another great supplement for these fish is live feeder fish, crickets and worms. Live fish and other live foods are a great way to get nutrients to your fish as well as make feeding exiting and bring out their natural hunting behaviors.

If you decide to use feeder fish, buy them from your local store and quarantine them in a separate tank for a few days. This lets you check that all of them are healthy and won’t introduce diseases into your tank.

Iridescent Shark Care Guide

Iridescent Shark in the Wild

To make sure your fish are happy and healthy, the water needs to be as clean as possible. Iridescent catfish are messy by nature and need a strong filter.

You can help with the filtration by changing 25% of the water weekly. This is one of the most time consuming duties of caring for your iridescent sharks. Understanding how much time you need to put in a tank is important. A tank like this will take more time due to the size, but it is well worth it.

When you carry out water changes, make sure you carry them out slowly so you don’t scare the fish and cause them to become stressed.

In terms of disease these catfish are susceptible to skin fungus and Ich. Being scale-less, it is harder to treat catfish with Ich than most other fish. You will see white dots all over your fish and they will rub their sides on the tank.

Medications are available to help cure fungus and ich; many will state to use the dosage at half strength for scale-less fishes.

Always try to get to the root of the cause as well as medicating them – it’s quite possible that their water quality isn’t great if they’re getting diseases.

How To Breed Iridescent Shark

Migrating Iridescent Shark

Because of their size and migrating behavior, these fish can not be bred in captivity. In the wild they will travel up stream to breed during the late summer months when the water levels rise.

They breed in huge ponds in Southeast Asia. This allows for these huge adults to spawn without lacking the room they need.

The conditions needed in order to replicate the natural breeding season are nearly impossible to replicate in captivity.

Migration alone is one aspect that is vital to these fish and not possible in home aquariums.

Because they are so hard to breed in captivity it increase the importance of conserving their wild habitat. This is becoming a problem as pollution and human infrastructure continue to impact their natural habitat.

Are Iridescent Sharks Suitable for your Aquarium? (Summary)

After reading this guide you should know the key care points about this fish; they are large and it will take a lot of time to keep their tanks clean.

Their size is what makes them truly hard to keep. Having a tank large enough to keep a fully-grown adult is something that only a few people can afford. Juveniles are smaller and will fit in smaller tanks; however you still need to be ready for this growth.

They are truly hardy fish when it comes to water conditions and fit perfectly with other larger fish.

Feeding these fish is easy because they will eat anything that fits into their mouths; just keep it varied.

Have you kept this fish before? Let us know how large yours grew in the comments section below…

Leave your vote

About Robert 329 Articles
Robert Woods is the creator of FishKeeping World, a third generation fish keeper and a graduate in animal welfare and behavior. He is also a proud member of the Association of Zoos and Aquariums, the Marine Aquarium Societies of North America and the Nature Conservancy.


  1. I’ve had 3 -4 sets of juvenile sharks, cool fish when they were small.. brought them @ Petco, PetSmart & other local pet stores in my area., UNTIL THEY GET BIGGER!! IF only I seen this information about 20 years ago!! I’ve had to replace 3 heaters, buy 2 more tanks { which in their frantic state by dashing around the tank} cracked my huge tanks! not to mention, eating EVERYTHING IN SIGHT!! These fish REQUIRE A 200 Gal.tank OR A POND TO KEEP THEM HAPPY & HEALTHY!! I hope this helps!!!

    • You’re right Allen, many people don’t realise how big these fish get when they first buy them. They need at least a 300 gallon tank or pond. Robert

  2. I had three of them years ago in a 55 gallon tank, they lived for a good 8 years in the tank before they died and they got to be a good 17″ each before I lost them, but at that time I don’t know allot about them, I have some now in a 55 gallon but am in the process of looking for a larger tank but only thing I find funny is they talk about feeding them flake food but my sharks do not go to the top for food I have to get sinking pellets or they will not eat.

  3. Hello, I must say I enjoyed reading the article and comments. I bought an Iridescent Shark unknowingly from Walmart because my step-son wanted to add it to his 20 gallon tank (mainly Silver Dollar fish) I must admit, I knew and know little about fish and how to care for them (particularly back then, March of 2007). The shark grew to about 12-13 inches and is perfect in appearance. He is still alive and well at over the 12 year mark. Unfortunately, not knowing what he was, he had remained in a 20 gallon tank by himself for many, many years. Very spastic indeed, however always responded to my voice for direction, and to calm him down. He use to great me at any side of the tank when I called his name (Bubba), and mist of the time swam to the top to eat flakes twice a day while I placed some directly in his mouth. I found it incredible then, and more so now that I read the above! Tank conditions were always poor because cleaning the gravel stressed him out too much in that small environment. When they worsened during water testing, I see ked help and after describing my Bubba, I was informed of what he was and to look it up! In doing so, I realized how very wrong I had been these last 12 years and brought him in (gingerly, as if he were my baby) to a specialized aquarium store a few miles down the road. Ironically enough, someone else donated an iridescent shark earlier that day! The other much bigger (rounder) and having a bad spine and veryall poor shape. However, he is such a friendly shark (at least for me). I named him Root. So, thinking I may have stunted the growth of my Bubba, I now am deciding on buying a 75 gallon tank so I can bring him back home. They leave the bright light on (blue light seemed to be the most tolerable) I see he is extremely stressed by that. I just wish I knew for sure if he was no longer going to get bigger due to his stunted growth and out grow the 75 gallon tank. Sorry for the long story. Love to hear opinions on whether or not he will grow much more.

    • Hi Alan, thanks for sharing your experience. It’s great that you were able to find this out and return him to the store while you prepare his new tank, despite his age. It’s hard to tell whether he will grow any more. Given his age I would be tempted to say that he won’t, however he is very small so you might find that given a larger tank and the right conditions that he may very well grow slightly. Thanks, Robert

  4. I have an iridescent shark that I purchased 32 years ago, he is now over 3 feet long and doing very well. He does however have a bump on his nose from running into his tank. He is now in a 300 gallon stock tank for cattle with a waterfall, he seems quite peaceful. I keep saying he but is there anyway to tell the sex of my fish his name is Fred, just wondered if I should change it.

    • Hi Virginia, females tend to be a be fatter than males, and are also slightly larger in color. Thanks, Robert

  5. I just had a 400 gal indoor pond built for my 25 year old ID shark. I have been through multiple tanks, the latest being a 6’x2’x2 1/2’ one that I had custom made for him, but he seems truly happy in this pond. These fish are a huge life commitment.

  6. My iridescent shark got its eyes filled with with some white cloudy type what exactly i dont know what is the problem i dont know please inform me whats the reason

    • Hi Million, the most likely cause is that the water conditions in your tank aren’t ideal. Have you performed checks on the ammonia, nitrites and nitrate levels? Thanks, Robert

  7. Could you clarify what you mean by these fish are “messy”? We got 3 recently but we are rethinking our purchase after reading this 😀

  8. I just bought one of these about a year ago. He is still only about 2 to 3 inches long in a 40 gallon tank. I’m upgrading to a 55 gallon this week. I’m so glad I found this article and comments. I had no idea what have. Thank goodness I already have a 300 gallon pond. When I bought him at one of the pet stores, PetSmart or Petco. Nobody knew what he was. There was no tag and he was the only one of his kind in the tank. Thank you for the information and am eager to take good care of my iridescent shark now that I know the proper way to care for him. Can’t wait to see him grow.

  9. I have a iridescent shark it’s 14 years old and been in many tanks. We have him in a tank now 300gals he is 20 inches long. Tank as 2 pumps one on each end. Got a another tank order for him 8×31/2 x 30 inches high.. right now he isn’t eating was wondering what is causing this.. we clean out the rocks with a small pump that sucks up the waste and food it sometimes scares him.. we replace the water that we take out .. there’s a alge eating in the tank with him fir as long as him.. this shark only eats wafer food he is a vegetarian wouldn’t eat live feeder fish or blood worms or shrimp.. what can I do to get him to eat.. advice please worried

Leave a Reply

Your email address will not be published.