The iridescent shark (Pangasianodon hypophthalmus) is a large freshwater fish species native to Southeast Asia. Despite its name, this fish is not related to sharks; it gets its name from its streamlined, shark-like appearance. In its native region, the iridescent shark is often farmed as a food source. However, in the USA and Europe, it is commonly kept as an aquarium fish.
In this article, you’ll learn how to care for iridescent sharks, including tank setup, feeding habits, suitable tank mates, and breeding practices. This guide is designed to help aquarists understand the unique challenges of maintaining this fish in captivity, given its size and specific care requirements.
Contents
Habitat in the wild
The iridescent shark (Pangasianodon hypophthalmus), also known as the pangasius shark, is a large species of freshwater catfish from the family Pangasiidae, commonly referred to as the shark catfish family. Although its streamlined body and dorsal fin give it a shark-like appearance, the iridescent shark is not related to true sharks, which belong to a completely different taxonomic group.
Native to Southeast Asia, the iridescent shark is found in the Mekong, Mae Klong, and Chao Phraya river basins, spanning the territories of Thailand, Vietnam, Laos, and Cambodia. In addition to its natural habitat, the fish is farmed in other parts of the world, including the USA, Bangladesh, Singapore, and the Philippines, where it is raised in flooded paddy fields and similar environments.
Iridescent sharks inhabit large rivers with sandy or rocky bottoms, swimming primarily in the middle water layers. Their respiratory system includes a specialized air-bladder, allowing them to survive in oxygen-poor environments. In the wild, they prefer slow-moving or still waters such as river floodplains and lakes, where dense vegetation, submerged tree roots, and other forms of cover provide both shelter and food. Interestingly, this species is known for a behavioral trait: when threatened, it sometimes feigns death to avoid predators.
Similar to other members of its genus, the iridescent shark is an anadromous species, meaning it migrates over long distances. It travels thousands of kilometers from its spawning grounds located upstream to its feeding and juvenile-rearing areas in the lower reaches of rivers.
The iridescent shark is omnivorous, feeding on a wide variety of plant and animal matter. In the wild, its diet consists of algae, seed plants, zooplankton, and insects, while adult fish consume larger items such as fruits, crustaceans, and small fish. This varied diet reflects the adaptability of the species to different environments.
In Southeast Asia, the iridescent shark is also an important food fish, particularly in countries like Thailand and Vietnam, where it is farmed extensively. Its firm, mild-flavored white meat is used in a range of culinary dishes, including soups, stews, and curries, as well as in fillet form. Additionally, it is one of the most commercially farmed freshwater fish species in Southeast Asia, known in international markets as “basa” or “swai.” The species’ versatility in both culinary and aquaculture contexts makes it a valuable resource across multiple regions.
Description
Juvenile iridescent sharks are particularly eye-catching due to their vibrant appearance. They feature two wide stripes that stretch along the entire length of their body, giving them a distinctive and appealing look. However, as the fish matures, these stripes gradually fade, and the overall body color becomes uniformly gray, with darker fins. The abdomen and mouth area develop a silvery sheen, while the fins take on a dark gray hue with silvery edging. The anal and tail fins also exhibit dark stripes.
As adults, their coloring becomes more subdued, and their large head and eyes, along with two pairs of barbels characteristic of catfish species, become more prominent. Additionally, albino variants of the iridescent shark can sometimes be found in the aquarium trade. These albino specimens have a pale, almost white appearance, which makes them stand out from their standard gray counterparts.
How big do iridescent sharks get?
The iridescent shark is a large freshwater fish that can grow up to 130 cm (4.3 ft) in length and weigh as much as 44 kg (97 lbs). In the wild, these fish commonly reach sizes between 3 and 4 feet (approximately 1 to 1.2 meters), though in rare cases, individuals may grow even larger.
In captivity, iridescent sharks can also grow to substantial sizes, with their growth largely influenced by the size of their aquarium and the quality of care they receive. Given enough space and ideal conditions, it is common for adult iridescent sharks in well-maintained aquariums to reach lengths of 2 to 3 feet (around 60 to 90 cm).
It is crucial for prospective owners to understand the potential size of these fish when considering them as pets. They require very large tanks—ideally over 300 gallons—to accommodate their growth and ensure their well-being. Providing a suitable environment, including ample swimming space and proper water quality, is essential to their health and longevity. As with any species, responsible care, research, and preparation are vital to ensure that the fish thrive in captivity.
How long do iridescent sharks live?
In the wild, iridescent sharks (Pangasianodon hypophthalmus) typically live for around 10 to 15 years. However, in captivity, where they benefit from consistent care and a controlled environment, they can live significantly longer. Some well-maintained aquarium specimens have been known to reach 20 years or more.
How fast do iridescent sharks grow?
The growth rate of iridescent sharks can vary significantly based on factors such as their environment, water quality, diet, and overall care. During the early stages of life, they grow rapidly, especially in the first few months. Juvenile iridescent sharks can typically grow between 2 to 4 inches (5 to 10 centimeters) in this initial period. By the end of their first year, they often reach 8 to 12 inches (20 to 30 centimeters) in length.
As they mature into their second and third years, the growth rate begins to slow. In captivity, they may grow several inches per year, depending on the quality of care and conditions provided. By the time they reach adulthood, usually around 3 to 4 years old, iridescent sharks can measure between 2 to 3 feet (60 to 90 centimeters) in length.
Providing optimal care, including a nutritious and varied diet, spacious aquariums, and clean water, is essential for supporting healthy growth. Juveniles can thrive in smaller tanks of around 100 gallons, but as they grow, a minimum tank size of 300 gallons is recommended to accommodate their adult size. Ensuring the right living conditions is crucial for their overall growth and long-term well-being.
| Characteristic | Description |
|---|---|
| Scientific Name | Pangasianodon hypophthalmus |
| Common Name | Iridescent Shark |
| Family | Pangasiidae |
| Habitat | Freshwater rivers, floodplains, and lakes |
| Native Range | Southeast Asia (Mekong and Chao Phraya basins) |
| Maximum Length | Up to 3-4 feet (1-1.2 meters) |
| Body Shape | Elongated, streamlined |
| Color | Dark gray to black, with iridescent scales |
| Scales | Iridescent, giving a shimmering appearance |
| Diet | Omnivorous, feeds on algae, plants, and detritus |
| Behavior | Generally peaceful, but can be active and fast-swimming |
| Temperature Range | 22°C to 28°C (72°F to 82°F) |
| Preferred Water Conditions | Neutral to slightly acidic pH, soft water |
| Aquarium Size | Requires a large tank due to its potential size |
| Tank Setup | Plenty of swimming space, hiding spots, and proper filtration |
| Breeding | Difficult to breed in captivity |
| Conservation Status | Not Evaluated (The species may face threats due to habitat loss and overfishing in the wild.) |
Difficulties in keeping
While the iridescent shark is relatively undemanding in terms of care, potential owners should carefully consider their ability to provide a suitable environment for this large fish. Adult iridescent sharks require exceptionally large tanks, and it is important to plan for this before making a purchase.
The idea of keeping an iridescent shark in captivity continues to spark debate among aquarists. Though it rarely reaches its full wild size in an aquarium, it can still grow up to 20 inches (50 cm) or more. Contrary to common belief, tank size does not directly limit their growth, making it vital to provide a tank large enough to accommodate their eventual size—at least 300 gallons for adults.
Despite their peaceful nature, iridescent sharks can only safely coexist with tank mates they cannot fit into their mouths. Water parameters are generally flexible, but maintaining clean, well-filtered water is essential for their health. These fish are omnivorous and will eat a wide variety of foods, including pellets, vegetables, and protein sources like shrimp or fish fillets.
One critical consideration is the iridescent shark’s timidity. They are prone to panic when startled, and due to their size, they can unintentionally damage tank walls or decorations if they thrash. Their skin is also soft and sensitive, so all sharp objects must be removed from the aquarium to prevent injury.
Keeping in a tank
Tank size
Juvenile iridescent sharks are often sold in pet stores due to their small, attractive size, which can make them appealing to buyers. However, sellers rarely inform buyers about how large these fish can grow or their long-term care needs. Iridescent sharks grow rapidly and can reach impressive sizes, requiring appropriately large tanks. Additionally, this species prefers to live in schools, meaning even more space is necessary to house multiple fish.
For juvenile iridescent sharks, a tank of at least 100 to 150 gallons (approximately 380 to 570 liters) is recommended to accommodate their initial growth. However, as these fish mature, they will quickly outgrow smaller tanks. Adult iridescent sharks require a tank of at least 300 gallons (approximately 1,135 liters) to ensure they have enough space to swim comfortably. Providing a spacious environment is crucial not only for their movement but also to help maintain better water quality and prevent stress related to overcrowding.
Iridescent sharks are highly active swimmers and must be kept in a school of at least five individuals to feel secure. This schooling behavior further increases the tank size requirements. For a proper setup that accommodates a group of adult fish, you may need a tank far larger than 300 gallons. Their high energy levels and social needs make them a challenging species to care for in a home aquarium.
If you are seriously considering keeping iridescent sharks, be sure to plan for their adult size and behavior to ensure you can provide them with the space and care they need to thrive.
Tank decor
When setting up a tank for iridescent sharks, an oblong shape is preferable to provide ample swimming space, as these fish are very active and require room to thrive. Using coarse sand as the substrate is ideal, and incorporating live plants can enhance the tank’s environment. Secure the plants firmly to the bottom, or place them in small flower pots buried in the substrate to prevent uprooting. Including decorations such as stones, driftwood, or unique shelters can provide hiding spots and enrichment.
However, caution is necessary when selecting decorations. Unlike many other fish species, iridescent sharks do not have protective bony plates; their skin is delicate and easily damaged. Choose decorations that pose no risk of injury to the fish.
It is also important to note that iridescent sharks have poor eyesight and can be quite skittish. Avoid tapping on the tank glass, as sudden noises can startle them, leading to panic. When frightened, these fish may thrash around the tank, potentially injuring themselves on the glass, decorations, or other fish.
After a panic episode, it is not uncommon to find the fish resting on the tank bottom, appearing beaten and limp. If you are fortunate, they may recover with time and proper care.
Water parameters
While these fish are relatively hardy, striving for water conditions that resemble their natural habitat is essential. Here are the recommended water parameters for keeping iridescent sharks:
Temperature
The ideal temperature range for iridescent sharks is between 22°C to 28°C (72°F to 82°F). As tropical fish, they prefer stable and warm water conditions.
pH Level
Aim for a slightly acidic to neutral pH level between 6.5 and 7.5. This range mimics the pH levels found in their native habitats.
Ammonia and Nitrite
Both ammonia and nitrite levels should be maintained at zero. These harmful substances can accumulate in the aquarium and become lethal to fish if present in high concentrations.
Nitrate
Keep nitrate levels as low as possible, ideally below 20 ppm (parts per million). Regular water changes and proper filtration are crucial for controlling nitrate levels.
Water Hardness
Iridescent sharks can tolerate a wide range of water hardness but generally prefer slightly soft to moderately hard water. Aim for a dGH (degrees of general hardness) level between 2 and 15.
Filtration
A powerful and efficient filtration system is essential due to the large size and waste production of iridescent sharks. Effective filtration helps maintain water quality and minimizes the accumulation of harmful substances.
Tank Size
Since iridescent sharks can grow quite large, a spacious aquarium is necessary to accommodate their growth. A tank size of at least 150 gallons (approximately 570 liters) is recommended for a single adult iridescent shark. If possible, larger tanks or pond setups are even better.
Regular water testing and maintenance are vital for monitoring and adjusting water parameters as needed. Providing ample swimming space, hiding spots, and compatible tank mates also contributes to a healthy and stress-free environment for iridescent sharks in captivity.
Diet
Iridescent sharks are omnivorous fish known for their hearty appetites; they will eat nearly everything they find. In the wild, their diet primarily consists of algae, plants, detritus (decaying organic matter), and small aquatic organisms like crustaceans and insects. In captivity, they accept a wide range of foods, including live, frozen, flake, and tablet options. A mixed diet is ideal, combining both vegetable and protein-rich components.
In captivity, it is essential to provide a well-balanced diet that includes a mix of plant-based and protein-rich foods. Commercially available sinking pellets or sticks designed specifically for catfish can serve as the staple of their diet. These pellets typically 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 important to ensure they receive a diverse range of nutrients. Suitable options for supplementary feeding include:
- Bloodworms
- Brine shrimp
- Daphnia
- Krill
- Chopped earthworms (in appropriate sizes)
- Spirulina-based fish flakes or pellets
- Blanched vegetables, such as zucchini, cucumber, or spinach
Feed iridescent sharks two to three times a day, providing portions they can consume within five minutes. Overfeeding can lead to water quality issues and health problems for the fish, so monitoring their eating habits and adjusting the amount of food accordingly is crucial.
Tank mates
Iridescent shark juveniles prefer to stay in schools, but as they mature, they tend to become more solitary. While iridescent sharks can coexist with tank mates of similar size or species they cannot swallow, they will view smaller fish as potential food. Additionally, they may disturb slower species or become intimidated by aggressive or predatory tank mates.
Choosing Suitable Tank Mates
When selecting tank mates for iridescent sharks, it’s important to consider their large size and semi-aggressive nature. Although they are generally peaceful fish, they may become stressed or territorial when housed with small, timid species that cannot handle their size and activity levels. It is also vital that tank mates thrive in similar water conditions and have compatible temperaments. Here are some suitable tank mates for iridescent sharks:
- Large Catfish: Other large catfish species, like the Plecostomus (commonly known as plecos), or other pangasiidae catfish, can be compatible companions.
- Bala Sharks: Bala sharks (Balantiocheilos melanopterus), which are not true sharks but large cyprinids, can coexist well with iridescent sharks due to their similar requirements.
- Giant Gouramis: Larger species of gouramis, such as the giant gourami (Osphronemus goramy), may also be suitable tank mates.
- Large Cichlids: Certain larger cichlid species, like oscars (Astronotus ocellatus) or severum (Heros severus), could work as long as they are not overly aggressive.
Monitoring Interactions
It’s crucial to closely monitor the interactions between the iridescent shark and its tank mates. If aggression or territorial behavior is observed, it may be necessary to rearrange the tank layout or provide additional hiding spots to reduce stress and potential conflicts.
Gender differences: male vs female
Identifying the sex of juvenile iridescent sharks (Pangasianodon hypophthalmus) can be quite challenging due to the lack of clear external sexual dimorphism at this stage. However, once they reach sexual maturity, certain characteristics become apparent that can help distinguish males from females. Here are some general traits to look for:
Size
In some cases, adult males may be slightly smaller than females, but this is not a reliable indicator for sexing.
Anal Fin Shape
Males typically have an elongated and pointed anal fin, while females have a more rounded anal fin.
Vent Shape
The vent, located behind the anal fin, may vary in shape. Males often have a more prominent and pointed vent, whereas females may have a more rounded vent.
Body Shape
Some experienced fishkeepers report that male iridescent sharks possess a more streamlined and slender body compared to females, although this can be subjective and not universally applicable.
It is crucial to note that these distinguishing characteristics may only become evident once the fish reach sexual maturity, which usually occurs several years after they have attained a certain size. As such, accurately sexing juvenile iridescent sharks can be quite difficult.
If you require precise identification for breeding or other specific reasons, consulting a professional aquarist or a veterinarian experienced in fish care is advisable. In general, iridescent sharks are kept in aquariums primarily for their beauty and social behavior rather than for breeding.
Breeding
Breeding iridescent sharks in captivity is quite rare due to their significant size and the specific requirements needed for a spawning tank. In the wild, these fish migrate downstream to their spawning grounds during late spring or early summer, a natural behavior that cannot be easily replicated in home aquariums.
Typically, commercial breeding occurs in expansive ponds at Asian fish hatcheries, as the conditions there more closely resemble their natural environment. Vietnam is particularly notable for exporting Pangasianodon hypophthalmus to over 80 countries, highlighting the challenges faced by individual aquarists looking to breed this species at home.