Iridescent Shark Catfish (Pangasianodon hypophthalmus)

Read this first: the Iridescent Shark grows to around a metre

The Iridescent Shark Catfish, Pangasianodon hypophthalmus, is sold at 4–5 cm, but it is one of the largest fish in the aquarium trade. Seriously Fish says it easily tops 90 cm in captivity and can live for 20 years or more, and FishBase records wild fish up to 130 cm and 44 kg. Seriously Fish gives at least 450 × 180 × 180 cm for one adult kept long term, and openly questions whether it should be kept as an aquarium fish at all. ScotCat goes further and describes it as not fit for aquarium use.

We are listing the iridescent shark for the few keepers who already run, or are building, an indoor system on that scale, such as a very large heated indoor pool or public-aquarium-style tank. If that is not you, please do not buy one: it will outgrow any ordinary aquarium, large catfish are very hard to rehome, and it must never be released.

Decide from the complete care picture

If you want a catfish that stays a manageable size, browse our catfish and plecos or our other catfish category, where most species stay a fraction of this size.

Know what it is and where it comes from

Despite the name, it is not a shark but a catfish in the family Pangasiidae, the shark catfishes. Its shark-like look comes from the tall, pointed dorsal fin, deeply forked tail and constant open-water swimming.

It is native to the lower Mekong in Thailand, Laos, Cambodia and Vietnam and to the Chao Phraya and Maeklong basins of Thailand. Seriously Fish describes it as a fish of the main river channels and larger tributaries that migrates upstream to spawn; FishBase adds that it moves upstream in the Mekong between May and July and returns to the main river between September and December. In the wild it eats fish, crustaceans and plant debris.

Most fish in the trade are mass-bred on farms in its native region, where the species is also farmed for food. Wild populations are in trouble: FishBase lists it as Endangered on the IUCN Red List (assessed 2011), and ScotCat notes it is nearly gone from the Chao Phraya and the Thai Mekong.

Recognise the names it is sold under

• Iridescent Shark or Iridescent Shark Catfish, the usual UK trade name.
• Siamese shark catfish and sutchi catfish, older hobby names.
• Striped catfish, the English name used by FishBase.
• Pangasius sutchi and Pangasius hypophthalmus, older scientific names still seen on labels.

Know exactly what you receive

One purchase quantity supplies one live Iridescent Shark Catfish, dispatched at 4–5 cm. Our photographs show an older fish to illustrate the species, not the size or the individual you will receive. Seriously Fish says females are supposedly stockier with lighter patterning, but these differences cannot be seen at sale size, so the sex is not specified.

Seriously Fish also notes selectively bred albino and "shortbody" or "balloon" forms. The shortbody form stays much smaller than the natural fish. This listing is the natural form, which grows to full size.

Plan for the fish it becomes

Plan housing for the adult, not the juvenile

Seriously Fish gives a minimum of 450 × 180 × 180 cm, about 14,580 litres, for a single adult kept long term, and says the species is unsuitable for all but the very largest tanks. A juvenile can be grown on in a smaller tank for a while, but the final home has to exist before the fish needs it. Seriously Fish is clear that the belief that fish only grow to fit their tank is a myth.

In England and Wales the genus Pangasianodon is on the government list of fish kept under a general licence that allows keeping in indoor aquaria only. It must never go into an outdoor pond or be released. If you are planning an indoor pool system rather than a glass aquarium, check with the Fish Health Inspectorate, through the GOV.UK non-native fish page, that your set-up is covered.

Check five things before you buy

1. The adult system exists or is being built: around 450 × 180 × 180 cm for one fish.
2. The building can take the weight: 14,580 litres of water weighs about 14.6 tonnes.
3. Filtration is sized for a metre-long fish: Seriously Fish recommends a large, efficient biological filter, preferably a sump.
4. You can commit for 20 years or more.
5. You have a plan that does not depend on rehoming: Seriously Fish says public aquaria are already overwhelmed and few hobbyists can take a large specimen.

Our tank volume calculator shows how far short a typical aquarium falls: a generous 180 × 60 × 60 cm home aquarium holds about 648 litres, under 5% of the Seriously Fish figure.

Furnish for a nervous, powerful swimmer

Seriously Fish says an adult needs no décor if the lighting is fairly dim, and that bogwood, beech branches or smooth rocks are optional extras. Anything you add must be too heavy to move or firmly fixed, and there must be plenty of open swimming space. The fish sometimes breaks the surface when agitated, so a heavy cover is essential, and it can smash glass heaters and thermometers.

Divide the system by function

Avoid sudden changes of light and movement close to the glass. A startled iridescent shark bolts, and in a cramped or cluttered system that is when injuries happen.

Set water values within the species range

Seriously Fish gives 22–26°C and pH 6.5–7.5, and says a hardness of about 2–30 degrees should be acceptable because its rivers vary with seasonal flooding. FishBase gives the same temperature and pH ranges and 2–29 dH. As a river fish, it needs well-oxygenated, moving water.

Compare your tap water with these values using our water matcher, and read the aquarium water chemistry guide if you are unsure what pH and hardness mean.

Separate habitat values from waste readings

The waste limits follow OATA's freshwater care sheets. A fish of this size produces a great deal of waste, so test at least weekly and more often while the fish is growing.

Size filtration for a metre-long fish

Seriously Fish recommends a large, efficient biological filter and says a sump is preferred. Plan filtration for the adult fish from the start, with strong water movement and plenty of surface agitation for oxygen.

Follow a weekly maintenance sequence

1. Test ammonia, nitrite and nitrate before maintenance.
2. Change at least 25% of the water each week, as OATA recommends, and more as the fish grows.
3. Treat new water with a conditioner for chlorine or chloramine and match its temperature.
4. Remove uneaten food and waste from the base.
5. Check flow, heater guards, cover fixings and pipework.
6. Rinse filter media only in removed aquarium water, never under the tap.

Our guide to aquarium filtration explains biological, mechanical and chemical filtration.

Feed protein while young and more greens as it grows

Seriously Fish describes the iridescent shark as omnivorous. Juveniles need a good amount of protein: chopped earthworm, bloodworm and dry pellets. Adults need more vegetable matter, such as spinach, frozen peas, Spirulina-based dry foods and occasional fruit.

Build one measured meal

• Young fish: a protein-rich sinking granule such as Krill Gran sinking food, with bloodworm or chopped earthworm.
• Growing and adult fish: more plant-based foods such as Super Spirulina Forte granules or a herbivore pellet, plus blanched spinach and peas.
• Portion: only what the fish clears within a few minutes; remove leftovers.
• Watch growth: a fast-growing fish is a reason to move the plan for its adult home forward, not to cut its food.

Introduce and settle a young fish

Confirm a mature filter, zero ammonia and nitrite and 22–26°C before the fish arrives. Acclimatise with the lights off: float the sealed bag for about 10 minutes, add small amounts of aquarium water over up to 20 minutes, then net the fish into the tank and discard the bag water. Keep the room quiet and the lights dim for the first days.

Use a first-week checkpoint plan

Our guide to acclimatising new fish has more detail, and our delivery information explains dispatch days and live arrival terms.

Watch for stress and injury

Seriously Fish and ScotCat both describe the iridescent shark as nervous and skittish. In cramped conditions it can injure itself by striking the glass and décor. Most problems with this fish trace back to space, sudden disturbance or water quality.

Pair each observation with an action

Plan its social needs honestly

Seriously Fish describes the iridescent shark as a shoaling species that is less flighty in a group, but points out that keeping several would need an enormous tank. That leaves a real dilemma: a lone fish is more nervous, and a group multiplies a space requirement that is already beyond a home aquarium.

Breeding in aquariums is considered unlikely because of its migratory spawning and the size of mature fish; it is bred commercially in large ponds on fish farms.

Balance social needs against space

• Social: it is calmer with its own kind.
• Space: one adult already needs around 450 × 180 × 180 cm.
• Biological: every extra fish adds a large waste load to filter.

Choose only large, calm tank mates

The iridescent shark is not aggressive, but it will eat much smaller fish, its constant activity can bother sedentary or shy fish, and boisterous species easily intimidate it. Seriously Fish suggests large, peaceful bottom-dwellers and mid- to upper-water shoaling fish, such as big doradid catfish (Oxydoras niger, Megalodoras uranoscopus and Pterodoras granulosus), pacu and larger cyprinids.

Screen every companion

These companions are large fish too, and their adult space needs add to the iridescent shark's. Check any combination with our tank mates tool, and look at our centrepiece fish for big, striking species that suit more realistic aquarium sizes.

Answer Iridescent Shark buying questions

How big does an Iridescent Shark get?

Seriously Fish says it easily tops 90 cm in captivity, though it rarely reaches 130 cm there. FishBase records wild fish up to 130 cm standard length and 44 kg. It is sold at 4–5 cm, so plan for the adult, not the juvenile.

What size tank does an Iridescent Shark need?

Seriously Fish gives at least 450 × 180 × 180 cm, about 14,580 litres, for one adult kept long term. That is far beyond any normal home aquarium.

How long does an Iridescent Shark live?

Seriously Fish gives a lifespan of around 20 years or more, so buying one is a commitment of two decades to a fish that will need a very large system.

Is the Iridescent Shark really a shark?

No. It is a catfish, Pangasianodon hypophthalmus, from the Mekong and Chao Phraya region. It only looks shark-like because of its tall dorsal fin, forked tail and constant swimming.

Will it stay small in a small tank?

No. Seriously Fish calls the idea that fish only grow to fit their tank a myth. In a cramped tank it becomes stressed, crashes into the glass and décor and can be badly injured.

What can live with an Iridescent Shark?

Only large, peaceful fish too big to swallow, such as pacu, big doradid catfish and larger cyprinids, in a system big enough for all of them. It will eat much smaller fish and is frightened by boisterous ones.

What does an Iridescent Shark eat?

It is an omnivore. Young fish need plenty of protein, such as pellets, bloodworm and chopped earthworm; adults need more vegetable matter, such as spinach, peas and Spirulina-based foods.

Can I rehome it if it gets too big?

Rarely. Seriously Fish says public aquaria are already overwhelmed with large unwanted fish and few hobbyists can take one. Please only buy it if you can house it for life, and never release it.

Consult the care references

• Seriously Fish: Pangasianodon hypophthalmus — adult size in captivity, minimum system for one adult, décor, filtration, cover, water range, juvenile and adult diet, behaviour, tank mates, lifespan, breeding, colour forms and the case against casual keeping.
• FishBase: Pangasianodon hypophthalmus — family, maximum length and weight, temperature, pH and hardness, distribution, migration, wild diet and IUCN status.
• ScotCat: Pangasianodon hypophthalmus — synonyms, sale size of juveniles, nervous behaviour, conservation notes and the view that it is not fit for aquarium use.
• OATA freshwater care sheets (barb sheet) — UK trade water-quality limits for ammonia, nitrite and nitrate, weekly maintenance and acclimatisation method.
• GOV.UK: Introduce or keep non-native fish and shellfish — licensing of non-native fish in England and the link to the list of fish that may be kept in indoor aquaria.
• GOV.UK: Freshwater fish that can be kept for ornamental purposes (list updated 13 October 2026) — lists the genus Pangasianodon under the general licence for indoor aquaria only (England and Wales).
• Tropical Fish Co delivery policy — current dispatch days and live arrival terms.