Iridescent Shark (Pangasionodon hypophthalmus) Care Sheet

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Have a big tank or pond and looking for a monster freshwater fish to fill it out? The endangered iridescent shark could be the right species for you.

The iridescent shark is a large river fish that needs lots of open water and room to grow to mature size. Because of their space demands, many hobbyists find themselves having to eventually rehome their fish. However, if you give the right care from the start, then the iridescent is a beautiful species to have in your home before it’s gone from the wild!

Keep reading to find out everything you need to know about iridescent sharks and how to keep one in your own freshwater tank or pond system!


Pangasionodon hypophthalmus is commonly known as striped catfish or iridescent shark and less often as the siamese shark or sutchi catfish; contrary to its common name, these fish are not true sharks and are not even closely related. Instead, they are part of the Siluriformes order of catfish

These fish belong to the Pangasianodon genus which only contains two species in total, with the other being the Mekong giant catfish (Pangasianodon gigas); the Mekong giant catfish is one of the largest known catfish species in the world and one of the largest freshwater fish ever recorded overall. 

As iridescent sharks are very popular in the commercial food industry, they are also referred to as swai. 

Natural habitat

The iridescent shark is native to the Mekong, Chao Phraya, and Maeklong River basins throughout Thailand, Cambodia, Laos, and Vietnam. These migratory fish can be found in the main channels of large rivers and tributaries and are known for traveling great distances upstream to spawn.

These sharks have also been introduced to other river regions throughout the world, like parts of North America, the Philippines, and Indonesia, as the result of aquacultural farming; it is believed that some introductions have been the result of aquarium releases. 

Conservation status

The iridescent shark is a very popular dish around the world. For the past several decades, these fish have been fished and farmed for their meat which has quickly led to overexploitation and dwindling numbers.

This, in addition to the installation of dams and other waterworks as well as the secondary pollution around their natural river basins, has almost certainly contributed to their struggling populations. 

In 2011, Pangasionodon hypophthalmus was listed as an endangered species by the IUCN Red List of Threatened Species.


Pangasionodon hypophthalmus

While the iridescent shark is easy to identify, it can be difficult to confirm the species at any given size due to the fast growth rate. These fish are usually varying shades of grey or brown, with the color lightening and you move towards their creamy-white underbellies; as the name suggests, these fish have an iridescent sheen to their skin which can make them appear different colors depending on the angle. 

Juveniles have the same body shape as adults but have a black stripe along their lateral line and another black stripe just under that line; it is believed that these areas of the fish contain sensory nerves that help monitor changes in water conditions. 

Growth rate 

While your iridescent shark might be small for the time being, this species isn’t known for being a monster fish for nothing. Catfish are opportunistic feeders for the most part and won’t hesitate to try to eat something if they can fit it in their mouth. As a result, they can grow as quickly as their conditions allow them to; remember that purposely stunting a fish and failing to give adequate diet or tank space is cruel and will greatly affect the lifespan of the fish. 

That being said, it is not unheard of for a juvenile to surpass a foot (30.5 cm) long in its first year. 

How big do iridescent sharks get?

So how big do these monsters truly get? 

The longest documented iridescent shark came in at about 3.6 feet (109.7 cm) long and weighing just about 97 pounds (44 kg). While they rarely reach this mature size in captivity, you can expect your iridescent sharks to surely surpass at least 1.5 feet (45.7 cm) as adults. 

Also, keep in mind that these fish can live to be 20 years old. 

Iridescent shark tank requirements

The iridescent shark is a huge fish that needs a huge tank, preferably a pond. Many hobbyists believe that they can house a couple of juvenile iridescent sharks in a 40 gallon (151.4 L) breeder tank to allow them to ‘grow out’. However, these fish start to grow out as soon as they’re added to the tank!

The preferred tank size for an iridescent shark is at least 300 gallons (1135.62 L); remember that these fish grow to at least 1.5 feet (45.7 cm) and the length, width, and height of the aquarium need to be able to accommodate turnarounds. If possible, these fish should be kept in an aquarium-standard showcase or a several thousand-gallon pond system.  

Otherwise, iridescent sharks are not difficult to care for and are relatively hardy fish. As a river species, they appreciate some water flow and adequate gas exchange to maintain oxygen levels. While they don’t need any standing structures, large pieces of cured bogwood, driftwood, and rocks may help make their setup seem more natural; hardy and fast-growing plant species may also be added, though your catfish may dig them up and occasionally eat them. 

It should also be noted that the Mekong, Chao Phraya, and Maeklong river conditions are often murky and full of sediment. As a result, these fish have lowered eyesight and have compensated with sensitive barbels and other sensory organs. In order to make your catfish feel at home in your tank or pond, it is best to have areas of shade and indirect light. 

Water parameters

Since these catfish are opportunistic feeders, they eat a lot and create a lot of waste. It is best to have an oversized sump system that can deal with large amounts of ammonia and other excess nutrients. 

Otherwise, they require the same conditions as many other fish in terms of water quality. The iridescent shark is a tropical fish and needs to be kept in a water temperature range of 72-79° F (22.2-26.1° C) with a relatively neutral pH between 6.5-7.5. 

Iridescent shark tank mates

As mentioned before, these sharks are opportunistic feeders and anything that they can fit into their mouth will be considered food. This means that smaller, less-active species need to be avoided. The good thing is that if you’re able to correctly house an iridescent shark, then you most likely have a lot of space to house other monster fish as well!

Some good tank mates for your iridescent shark might be:

  • Bichirs (ornate bichir, Polypterus ornatipinnis)
  • Oscars (Astronotus ocellatus)
  • Common pleco (Hypostomus plecostomus)
  • Gars (alligator gar, Atractosteus spatula; Florida gar, Lepisosteus platyrhincus; spotted gar, Lepisosteus oculatus)
  • Clown knife (Chitala ornata)
  • Pacu (Serrasalmidae family)
  • Giant gourami (Osphronemus goramy)
  • Arowana (Osteoglossidae family)

Keep in mind that most of these fish can and will grow well over a foot (30.5 cm) long and do best in huge ponds, commercial aquariums, and in their wild habitats. Never purchase one of these fish without having an aquarium upgrade somewhere down the line in the future.

Too often, these species are released into the wild which introduces and increases invasive species populations that can lead to devastating effects on local ecosystems. Most commercial aquariums are also filled to capacity and cannot accept larger fish. 

Iridescent shark behavior

As juveniles, these fish stay in schools of four or five. However, this can become a problem once they start to grow. If you don’t have a pond system, it’s recommended to get one young adult as these fish can live solitary lives once they reach maturity. 

Otherwise, these fish can usually be found in the middle water column, and are relatively active swimmers. While these fish will always be out and about in the aquarium, they scary very easily. This can cause them to run into decorations or the aquarium glass at full speed, causing injury in the process. In order to prevent this as much as possible, it’s best to keep the aquarium light dimmed at all times and make sure that there is a lot of open water space with little to no sharp objects. 

Are iridescent sharks aggressive? 

Iridescent sharks are not aggressive fish by nature; this means that they won’t defend a territory or chase similar-looking fish. However, due to their poor eyesight and curious appetite, they do end up eating a lot of smaller tank mates which can initially come off as aggressive behavior to inexperienced hobbyists. 

Are iridescent sharks nocturnal?

If you’ve had a catfish before, you probably know that these fish typically become more active once the aquarium lights go off. However, the iridescent shark seems to be one of the few species that is just as active during the day. 

Still, some hobbyists have found that their iridescent sharks hide during the day; this could be the result of stress from poor water quality, overly active tank mates, or bright lighting. If everything in your tank is testing right and tank compatibility and aquarium setup is appropriate, then you could also just have a fish that prefers to be more active during the night. 

Why is my iridescent shark swimming upside down?

Iridescent Shark in large tank

While iridescent sharks usually behave themselves, hobbyists have reported some strange behavior from them. These fish tend to change personalities every day, and you might see them doing something weird from time to time. Some hobbyists have accredited this to the result of stunted growth in the aquarium trade, while others believe that it’s most likely due to injury or stress. 

If you find that your iridescent shark is swimming erratically, make sure to check all water parameters immediately. Next, check for any external signs of injury, disease, or other odd behavior; this may include areas of redness and swelling, white spots, and labored breathing or lethargy.

Also, make sure to check for signs of swim bladder disease. This disease affects the swim bladder which is the organ responsible for regulating buoyancy. As a result, the fish is not able to control its orientation in the water column which can lead to your fish swimming upside down or on its side. Along with this, the fish may have a swollen abdomen.

If water quality is good and there are no noticeable signs of something being wrong, continue to assess the health of your iridescent shark and of all the fish in your aquarium. Sadly, sometimes the problem can be internal, and very little can be done in time. But sometimes, your iridescent shark wants to play dead and scare you for no apparent reason. 

As long as you’re giving the best iridescent shark care as possible, there should be little reason to worry! 

Iridescent shark diet

Iridescent sharks are constantly growing. What does this mean? They need a lot of food.

Iridescent sharks are large omnivores that will eat any plant or animal matter that they happen to come across in the water current. 

Interestingly, juvenile iridescent sharks have teeth. These teeth are used to cut and tear meatier foods while they are young. As they grow into their adult size, they lose these teeth and tend to prefer more plant-based foods and prey that they can swallow whole. 

In the aquarium setting, these fish are fun to feed. As long as the diet is varied and high-quality, there isn’t much that you can’t feed them. It’s best to provide a daily catfish pellet as the staple of the diet to make sure that your fish is getting all the important nutrients. Otherwise, you may offer live, frozen, and freeze-dried worms (earthworms, bloodworms), shrimp (mysis shrimp, brine shrimp, as well as krill), and insects (mealworms, crickets). 

In addition, you may offer frozen seafood from your grocery store, like pieces of fish and other mollusks. Many hobbyists like to occasionally offer live foods, like smaller fish, in order to make their shark exhibit natural predatory behaviors and well as to keep them interested in certain foods. 


The iridescent shark is commonly sold as a beginner fish, however, this monster species is nowhere close to being easy. At adult size, these fish can reach almost 4 feet (121.9 cm)! That means that you will either need a several thousand-gallon tank or a huge pond system that your fish can live in for its full 20 years. 

Besides accomodating for their size, they are schooling fish as juveniles and need to be kept in small groups which demands even more space. Though they can be separated as adults, they can often be clumsy and need a wide variety of foods.

If you have any questions about iridescent sharks, caring for monster fish, or have had experience with large aquarium systems, don’t hesitate to leave a comment below! 

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