Size Matters: Understanding Iridescent Shark Growth and Tank Needs

Iridescent shark (Pangasianodon hypophthalmus) is a large freshwater fish that resembles a shark in some way, which if fact is the reason why the fish is called so. In South-East Asia this fish is grown to cook it, but in the USA and Europe this fish is often kept in tanks. Further in the article, you’ll find out how to keep iridescent shark fish, feed it, select tank mates, and breed it.

Habitat in the wild

The iridescent shark, also known as Pangasianodon hypophthalmus, is a species of freshwater catfish belonging to the family Pangasiidae. The Pangasiidae family is commonly referred to as the shark catfish family, due to the resemblance of some of its members to sharks in appearance. However, it’s important to note that these catfish species are not related to true sharks, which belong to a completely different taxonomic group.

The Pangasiidae family includes several species of large, freshwater catfish, most of which are native to Southeast Asia. The iridescent shark inhabits in Mekong, Mae Klong and Chao Phraya river basins in the territory of Thailand, Vietnam, Laos and Cambodia. The fish is also bred in the USA (in the paddy fields), Bangladesh, Singapore and Philippines.

The pangasius shark is encountered in large rivers with sandy or rocky bottoms; it swims in the middle water layers. It breathes using its gills and due to special structure of its air-bladder. The fish is quite active and timid at the same time; if it feels danger it pretends to be dead. In the wild, iridescent sharks prefer slow-moving or standing waters, such as the lower reaches of rivers, floodplains, and interconnected lakes. They are typically found in areas with dense vegetation, submerged tree roots, and other forms of cover where they can hide and find food.

Similar to other Pangasianodon kind representatives, this is an anadromous species that performs long-distance migration. It travels thousands of kilometers from its spawning areas that are located upstream to the places where it feeds and where its juveniles grow in the lower reaches of a river.

This species is an omnivorous one, it feeds on algae, seed plants, zooplankton and insects. Adult species also eat fruit, crustaceans and fish.

The iridescent shark (Pangasianodon hypophthalmus) is indeed consumed as food in some parts of the world, particularly in Southeast Asia, where it is native. In certain countries like Thailand and Vietnam, it is a popular food fish and is often farmed for its meat.

The meat of the iridescent shark is white, firm, and mild-flavored, making it suitable for various culinary preparations. It is commonly used in soups, stews, curries, and as fillets in many traditional dishes.


The juveniles are especially attractive, they have two wide stripes that stretch all over the body. However, the adult species have paler coloring and the stripes disappear. Their body coloring becomes uniformly gray and the fins are dark. The abdomen and the mouth are silvery colored. You may also encounter albinotic species of the fish on sale.

The fins are dark gray with silvery edging, anal and tail fins have dark stripes. The head and eyes are large. The fish has two pairs of barbels like those of a catfish.

How big do iridescent sharks get?

Iridescent shark is a large freshwater fish. It can be up to 130 cm (4.3 ft) long and weigh 44 kilos (97.0 lb). In the wild, they have been known to reach lengths of up to 3 to 4 feet (approximately 1 to 1.2 meters). However, in some rare cases, individuals may even exceed this size.

In captivity, iridescent sharks can also grow quite large, and their size is often influenced by the size of the aquarium they are kept in and the quality of care provided. Given enough space and proper conditions, they can still reach impressive lengths, and it’s not uncommon to see adult iridescent sharks around 2 to 3 feet (around 60 to 90 centimeters) in well-maintained aquariums.

It’s essential to be aware of their potential size when considering keeping iridescent sharks as pets. They require a large tank to accommodate their growth adequately, and providing a suitable environment is crucial to their well-being and health. As with any species, proper research and preparation are necessary to ensure they are cared for responsibly and have the best chance to thrive.

How long do iridescent sharks live?

In the wild, the lifespan of iridescent sharks (Pangasianodon hypophthalmus) is typically around 10 to 15 years. However, in captivity, where they receive proper care and suitable living conditions, they can potentially live longer. Some well-maintained aquarium specimens have been known to live up to 20 years or more.

The lifespan of any fish, including iridescent sharks, can be influenced by various factors, such as water quality, diet, tank size, stress levels, and overall health. Providing a spacious and adequately filtered aquarium with suitable hiding spots and maintaining good water parameters can contribute to their well-being and longevity.

It’s essential to recognize that taking care of iridescent sharks and any other large fish species is a long-term commitment, as they can live for many years. Before considering them as pets, ensure that you have the resources and dedication to provide proper care throughout their lifespan.

How fast do iridescent sharks grow?

The growth rate of iridescent sharks can vary depending on several factors, including their environment, water quality, diet, and overall care. In the first few months of their lives, they tend to grow relatively quickly, but their growth rate slows down as they mature.

In optimal conditions, juvenile iridescent sharks can grow around 2 to 4 inches (5 to 10 centimeters) in the first few months of life. During the first year, they can reach sizes of approximately 8 to 12 inches (20 to 30 centimeters) in length.

As they enter their second and third years, their growth rate starts to slow down. In captivity, they may grow at a rate of a few inches per year, depending on various factors. By the time they reach adulthood, which is usually around 3 to 4 years old, they can be about 2 to 3 feet (around 60 to 90 centimeters) long.

It’s essential to provide iridescent sharks with adequate space, a proper diet, and suitable living conditions to support healthy growth. Remember that these fish can grow quite large, and they require a spacious aquarium to accommodate their size throughout their lifespan. Providing optimal care can contribute to their overall growth and well-being.

Scientific NamePangasianodon hypophthalmus
Common NameIridescent Shark
HabitatFreshwater rivers, floodplains, and lakes
Native RangeSoutheast Asia (Mekong and Chao Phraya basins)
Maximum LengthUp to 3-4 feet (1-1.2 meters)
Body ShapeElongated, streamlined
ColorDark gray to black, with iridescent scales
ScalesIridescent, giving a shimmering appearance
DietOmnivorous, feeds on algae, plants, and detritus
BehaviorGenerally peaceful, but can be active and fast-swimming
Temperature Range22°C to 28°C (72°F to 82°F)
Preferred Water ConditionsNeutral to slightly acidic pH, soft water
Aquarium SizeRequires a large tank due to its potential size
Tank SetupPlenty of swimming space, hiding spots, and proper filtration
BreedingDifficult to breed in captivity
Conservation StatusNot Evaluated (The species may face threats due to habitat loss and overfishing in the wild.)

Difficulties in keeping

Though the iridescent shark is quite undemanding one, still before buying it you’d better think twice. The thing is that for the adult species you will need a really huge tank.

The idea of keeping iridescent shark in a tank still stirs up controversy. Though in captivity this fish very seldom reaches the size it can be in the wild, but yet it grows to be rather large (up to 20 inches long). At that the tank size doesn’t influence their growth rate. The iridescent shark is peaceful enough, but only towards tank mates that it can’t eat. Tank water parameters are of no significance for the fish, but the water has to be clean. Pangasius shark will everything you give to it.

The iridescent shark is a very timid one and considering its size it is quite capable to break the tank wall if it panics. Iridescent shark has very soft skin that can be easily damaged, therefore you should remove all sharp objects from the tank.

Keeping in a tank

Tank size

On sale you may often see juveniles – they are small and attractive, which makes buyers interested. However, the sellers don’t say how large the fish can grow. Iridescent shark becomes extremely large and it requires proper sized tanks. Besides this fish prefers living in a school and it means that far more space in a tank is required.

For juvenile iridescent sharks, a large aquarium of at least 100 to 150 gallons (approximately 380 to 570 liters) is necessary to accommodate their initial growth. As they mature, they will quickly outgrow smaller tanks, so it’s important to plan for their adult size from the beginning.

Ideally, adult iridescent sharks should be kept in a tank of at least 300 gallons (approximately 1,135 liters) or more. Providing them with a spacious environment not only allows them to swim freely but also helps to maintain better water quality by diluting waste and preventing crowding-related stress.

Another thing is that pangasius shark is very active and it needs a lot of space to swim and it has to be kept only in a school of its kind. The fish feels comfortable in a school of at least 5 species, can you imagine how huge the tank should be? Well, if you after all decided to have iridescent shark as a pet, then…

Tank decor

The tank is desirable to have oblong shape – the fish is very active and spry, they need a lot of room to swim. Put coarse sand on the tank bottom, you may also add some live tank plants (you should fix them tightly to the bottom or put in small flower pots and dig into the substrate). Also it is desirable to put some decorations in the tank, for example, stones, snags or shelters of unusual spape.

However, be careful with the latter, since iridescent shark unlike other fishes isn’t covered with protective bony plates, which means that its skin is quite thin an it is easily damaged. Therefore, choose decorations that can’t hurt the fish.

Be careful! Iridescent shark has very poor eyesight, it is a very nervous fish easily scared. Don’t knock on the tank glass, the fish may hurt itself while its crazy panic attack. Frightened fishes hysterically rushes all around the tank hitting the glass walls, decorations and other fishes.

After the panic attack is over you may see the fish lying on the tank bottom beaten and limpen. If you are lucky, the fish will recover in time.

Water parameters

Maintaining appropriate water parameters is crucial for the health and well-being of iridescent sharks (Pangasianodon hypophthalmus) in an aquarium setting. While they are hardy fish, it’s essential to strive for water conditions that resemble their natural habitat. Here are the recommended water parameters for keeping iridescent sharks:

  1. Temperature: The ideal temperature range for iridescent sharks is between 22°C to 28°C (72°F to 82°F). They are tropical fish and prefer stable and warm water conditions.
  2. pH Level: Aim for a slightly acidic to neutral pH range, around 6.5 to 7.5. This range mimics the pH levels found in their native habitats.
  3. Ammonia and Nitrite: Both ammonia and nitrite should be kept at zero. These are harmful substances that can accumulate in the aquarium and can be lethal to fish if present in high concentrations.
  4. Nitrate: Keep nitrate levels as low as possible, ideally below 20 ppm (parts per million). Regular water changes and proper filtration can help control nitrate levels.
  5. Water Hardness: Iridescent sharks can tolerate a wide range of water hardness, but they generally prefer slightly soft to moderately hard water. Aim for a dGH (degree of general hardness) level between 2 to 15.
  6. Filtration: A powerful and efficient filtration system is essential due to the large size and waste production of iridescent sharks. Adequate filtration helps maintain water quality and reduces the accumulation of harmful substances.
  7. Tank Size: As iridescent sharks can grow quite large, a spacious aquarium is necessary to accommodate their growth adequately. A tank size of at least 150 gallons (around 570 liters) is recommended for a single adult iridescent shark. Larger tanks or pond setups are even better if possible.

Regular water testing and maintenance are essential to monitor and adjust the water parameters as needed. Additionally, providing plenty of swimming space, hiding spots, and appropriate tank mates can contribute to a healthy and stress-free environment for iridescent sharks in captivity.


Iridescent sharks are omnivorous fish, it is famous for this feature – it will eat everything it finds. It is gluttonous as well. In the wild, they primarily feed on algae, plants, detritus (decaying organic matter), and small aquatic organisms like crustaceans and insects. In a tank it eats all types of food – live, frozen, flakes, tablets. Mixed feeding is the best idea for diet – combine vegetable and live components.

In captivity, their diet should be well-balanced and provide a mix of plant-based and protein-rich foods. Commercially available sinking pellets or sticks specifically designed for catfish can serve as the staple diet. These pellets often contain a blend of vegetable matter, proteins, vitamins, and minerals to meet their nutritional needs.

Supplementing their diet with fresh or frozen foods is also essential to ensure they receive a diverse range of nutrients. Some suitable options for supplementary feeding include:

  1. Bloodworms
  2. Brine shrimp
  3. Daphnia
  4. Krill
  5. Earthworms (chopped into appropriate sizes)
  6. Spirulina-based fish flakes or pellets
  7. Blanched vegetables such as zucchini, cucumber, or spinach

Feed the iridescent shark twice or three times a day, but with portions it can eat in 5 minutes. Overfeeding can lead to water quality issues and health problems for the fish. Monitor their eating habits and adjust the amount of food accordingly.

It’s crucial to provide a well-balanced diet and ensure they receive adequate nutrition for their growth and overall health, especially if you plan to keep them in an aquarium for an extended period. Always research the specific dietary needs of any fish species you keep and consult with a knowledgeable aquarium expert or veterinarian if you have any concerns about their diet or health.

Tank mates

The iridescent shark juveniles stay in a school, but the older the fish becomes the more it tends to stay alone. Iridescent shark gets alone well with tank mates of the same size or the fishes they can’t swallow. Pangasius shark will treat any small fishes as food. It may disturb slow species or vice versa it can be scared by aggressive and predatory tank mates.

When choosing tank mates for iridescent sharks, it’s essential to consider their large size and semi-aggressive nature. While they are generally peaceful fish, they may become stressed or territorial if kept with small, timid species that can’t handle their size and activity level. Additionally, the tank mates should be able to thrive in similar water conditions and have compatible temperaments. Here are some suitable tank mates for iridescent sharks:

  1. Large Catfish: Other large catfish species like the Plecostomus (commonly known as Plecos) or other Pangasiidae catfish may be suitable companions.
  2. Bala Sharks: Bala sharks (Balantiocheilos melanopterus), which are not true sharks, but rather large cyprinids, can be compatible tank mates as they share similar requirements.
  3. Giant Gouramis: Some larger species of gouramis, such as the Giant Gourami (Osphronemus goramy), may coexist with iridescent sharks.
  4. Large Cichlids: Certain larger cichlid species like Oscars (Astronotus ocellatus) or Severum (Heros severus) could work as long as they are not overly aggressive.

It’s crucial to monitor the interactions between the iridescent shark and its tank mates closely. If aggression or territorial behavior is observed, it may be necessary to rearrange the tank or provide additional hiding spots to reduce stress and potential conflicts.

Remember that the tank size is essential when considering tank mates for iridescent sharks. Due to their large size and active nature, they require a spacious aquarium with plenty of swimming space and hiding spots. Always research the specific requirements and temperaments of potential tank mates before adding them to the same aquarium.

Gender differences: male vs female

Determining the sex of juvenile iridescent sharks can be challenging, as they do not exhibit clear external sexual dimorphism until they reach maturity. However, once they become sexually mature, there are some differences that can help differentiate between males and females. These differences are more apparent in adult iridescent sharks. Here are some general characteristics that can be used to distinguish between male and female iridescent sharks:

  1. Size: In some cases, adult male iridescent sharks can be slightly smaller than females, but this is not a reliable method of sexing them.
  2. Anal Fin Shape: Males tend to have a more elongated and pointed anal fin compared to females, whose anal fin is typically more rounded.
  3. Vent Shape: The vent, the opening located behind the anal fin, may have slightly different shapes in males and females. Males may have a more prominent and pointed vent, while females may have a more rounded vent.
  4. Body Shape: Some experienced fishkeepers claim that male iridescent sharks have a more streamlined and slender body compared to the females, but this can be subjective and not universally applicable.

It’s important to note that these characteristics might not be evident until the fish reach sexual maturity, which occurs when they are several years old and have reached a certain size. Additionally, sexing iridescent sharks based on external characteristics can be challenging and not always accurate, especially in juveniles. If you need to know the sex of your iridescent sharks for breeding purposes or other specific reasons, it may be best to consult a professional aquarist or a veterinarian experienced with fish to perform a more accurate examination. In most cases, iridescent sharks are kept in aquariums for their aesthetics and not for breeding purposes, so distinguishing their sex might not be a major concern for regular aquarium hobbyists.


Breeding the iridescent shark in captivity is very seldom the case due to the size and requirements to the spawning tank. In the wild pangasius migrates downstream to its spawning grounds, it happens in late spring or early summer. Such conditions can’t be simulated in a home aquaria. Usually, the fish is bred in huge ponds of Asian fish hatcheries, since only Vietnam exports Pangasius hypophthalmus to more than 80 countries.