Iridescent Shark: Profile, Facts, Size, Traits, Catfish, Tank, Diet

iridescent shark

The iridescent shark, known scientifically as Pangasianodon hypophthalmus, is a fascinating species of shark catfish that hails from the freshwater rivers of Southeast Asia. Despite its common name, this creature is not a true shark. It belongs to the Pangasiidae family, which includes various types of catfish. The name “iridescent shark” likely derives from its sleek, shark-like body and the shimmering, reflective quality of its skin, which glistens under the light, creating an iridescent effect. This attribute makes it visually striking, adding to the intrigue surrounding its name. The term “iridescent” refers to the way its scales change color depending on the angle of the light, similar to the way light dances off a soap bubble or a butterfly’s wings. This misleading name often confuses people into thinking it is a marine predator, when in fact, it is a peaceful freshwater fish.

Iridescent Shark: Profile, Facts, Size, Traits, Catfish, Tank, Diet

The meat is commonly marketed beneath the frequent title swai. It has additionally been launched into different river basins as a meal supply, and its placing look and iridescence have made it well-liked with fishkeeping hobbyists, amongst whom it’s also referred to as the Siamese shark or sutchi catfish. Swai’s omnivorous food regimen consists of crustaceans, different fish, and plant matter.

Natural Habitat: Rivers of Southeast Asia

The iridescent shark is primarily found in the rich, flowing waters of the Mekong basin and the Chao Phraya River. These rivers provide an ideal environment with abundant food and suitable conditions for breeding. The Mekong River, one of the longest in the world, flows through several countries including Vietnam, Thailand, Cambodia, and Laos, offering a vast habitat for these fish. The Chao Phraya River, coursing through Thailand, also supports a significant population of iridescent sharks.

These rivers are characterized by their warm, nutrient-rich waters which are teeming with aquatic life, providing a plentiful food supply. The seasonal flooding of these rivers creates a dynamic habitat, supporting the life cycle of various species including the iridescent shark. The fish thrive in these conditions, using the river currents to navigate and migrate to spawning grounds.

Cultivation for Food: A Vital Resource

In addition to its natural habitat, the iridescent shark is extensively farmed in Southeast Asia, playing a crucial role in the region’s aquaculture. It is highly valued for its meat, which is a staple in the diets of many local communities. The cultivation of iridescent sharks is a significant industry in countries like Vietnam and Thailand, where fish farms are specifically designed to breed and raise these catfish. These farms use large ponds or enclosures within the rivers, ensuring a controlled environment that mimics their natural habitat as closely as possible.

The farming process involves feeding the fish a diet that promotes rapid growth and maintaining water quality to prevent disease. The meat of the iridescent shark is tender and mild-flavored, making it a popular choice for various culinary dishes. It is often used in soups, stews, and grilled dishes, contributing to the local economy and providing a reliable source of protein for many families. The farming practices also support numerous jobs, from fish farmers to those involved in processing and distribution, highlighting the economic importance of this species beyond its ecological role.

Names: The Glow and Shark-Like Appearance

The iridescent shark gets its name from two distinctive characteristics observed in juveniles: their radiant glow and their shark-like appearance. Young iridescent sharks exhibit a shimmering, iridescent quality on their skin, reflecting light in a manner that creates a captivating display of colors, much like the surface of a pearl or a soap bubble.

This glowing effect is particularly striking and contributes to the common name “iridescent.” Additionally, despite being a catfish, the streamlined body shape and dorsal fin of this species resemble those of true sharks, leading to the second part of its name. This combination of a luminous, almost magical appearance in the young fish and a shape reminiscent of more notorious marine predators results in the evocative name “iridescent shark,” capturing both its beauty and its distinctive form.

Iridescent Shark Size: Growth and Appearance

As they grow, iridescent sharks can reach impressive sizes. Adult iridescent sharks can attain lengths of up to 130 centimeters (approximately 4.3 feet) and can weigh as much as 44 kilograms (97 pounds). These dimensions make them one of the larger species within the Pangasiidae family. Initially, the young fish exhibit a shiny, iridescent coloration that sparkles under light, which is the trait that gives the species its name. However, as they mature, their appearance changes significantly. Large adults lose their iridescence and become uniformly gray.

Their fins, which are dark gray or black, provide a stark contrast to their bodies. Juveniles have additional distinctive markings, including a black stripe along the lateral line of their body and a second black stripe beneath it. These stripes fade as the fish grow older, contributing to the transformation in appearance from colorful juveniles to more somber-looking adults.

Distribution and Habitat: A Migratory Lifestyle

The iridescent shark, or Pangasianodon hypophthalmus, is native to the expansive river systems of Southeast Asia, particularly the Mekong and Chao Phraya rivers. These rivers are essential to the life cycle of the species, providing a rich and varied habitat. The fish undertake significant migrations throughout the year, moving in response to the seasonal changes in the river environments. In the Mekong River, the iridescent sharks migrate upstream from March to May.

This period corresponds with the end of the dry season and the beginning of the rainy season when the rivers swell with fresh water and become more navigable. From May to September, during the monsoon season, they are found in different parts of the river, taking advantage of the abundant food supply. As the waters recede from October to February, the fish migrate downstream. These migrations are crucial for breeding and ensuring access to food resources. Each phase of their migratory pattern aligns with changes in water levels and flow, demonstrating their adaptation to the dynamic river ecosystems they inhabit.

Iridescent Sharks in the Magdalena River

In August 2015, an environmental group in Santander, Colombia, confirmed a troubling discovery: iridescent sharks were found in a tributary feeding into the Magdalena River. This occurrence was attributed to accidental releases from illegal farm fisheries in the region. The presence of these non-native fish has caused considerable concern among scientists and government officials. The Magdalena River is a vital ecosystem, home to over 200 native fish species, 35 of which are endangered.

The introduction of iridescent sharks poses a significant threat to these indigenous species, as they could disrupt local food webs and compete for resources. The ecological balance of the river is delicate, and the introduction of an invasive species could have far-reaching consequences, including the potential extinction of already endangered native fish.

Impressive Size and Unique Appearance

Iridescent sharks are notable for their substantial size and striking appearance. Adults can grow up to 130 centimeters (approximately 4.3 feet) in length and weigh as much as 44 kilograms (97 pounds). Their name is derived from the shiny, iridescent coloration of their skin, particularly visible in juveniles.

This shimmering effect, caused by light reflecting off their scales, gives the fish a visually appealing, almost magical look. However, as they mature, their coloration becomes more uniform and gray. Despite this, the dark gray or black fins maintain their striking contrast. The juveniles exhibit distinct black stripes along and beneath the lateral line, which gradually fade as they grow. This transformation in appearance from youth to adulthood is one of the many fascinating aspects of this species.

Market Names and Reputation

Despite their lack of a gourmet reputation, iridescent sharks are marketed under various names worldwide, reflecting their economic significance. In the United States, they are commonly sold as swai (pronounced /swaɪ/), while in Europe, they are known as panga or pangas. In several Asian countries, they are referred to as cream dory or basa. These different names help to market the fish to diverse consumer bases. Although not regarded as a premium fish, the total export value of pangasius from Vietnam reached an impressive US$1.8 billion in 2014. This significant figure underscores the importance of pangasius in the global seafood market, despite its modest reputation. The fish’s affordability, combined with its versatility in cooking, makes it a staple in many households.

Culinary Appeal and Versatility

Pangasius fillets have become increasingly popular due to their low cost, mild flavor, and firm texture. These characteristics make them an excellent substitute for other whitefish such as sole or halibut, allowing for easy adaptation of recipes. The fish’s delicate taste and texture appeal to a wide range of culinary preferences, making it a versatile ingredient in various dishes. Pangasius is often used in soups, stews, grilled preparations, and even in fried fish recipes. Its adaptability and economic value have cemented its place in the seafood market, making it a reliable and accessible option for consumers around the world.

Dietary Habits and Farming

Pangasius is an omnivorous species, meaning it has a diverse diet that does not heavily rely on animal protein. This dietary flexibility makes it easier and more cost-effective to farm. Typical grading sizes for pangasius fillets are 3–5 ounces, 5–7 ounces, and 7–9 ounces, catering to different market demands and culinary uses. The ability to grow well on a varied diet and the efficiency of farming practices contribute to the low cost of production, which in turn keeps the market price affordable. This economic aspect, combined with the fish’s culinary versatility, ensures that pangasius remains a popular choice for both consumers and aquaculture operations.

iridescent shark, Pangasianodon hypophthalmus

Spawning Area: Southern Mekong Inhabitants

The shaded area between Khone Falls and Kratie is a crucial spawning ground for the southern population of iridescent sharks. This stretch of the Mekong River provides ideal conditions for reproduction, with its complex system of rapids, deep pools, and varied riverbed structures.

During the spawning season, the fish gather in this area, taking advantage of the high water levels and increased flow to lay their eggs in the safety of the river’s depths. The specific environmental conditions of this region, such as the temperature, water chemistry, and flow dynamics, create a perfect habitat for the early life stages of the iridescent shark. The young fry benefit from the abundant food supply and shelter provided by the intricate riverine environment, which supports their growth and development until they are ready to embark on their migratory journey downstream.

Origins and Aquaculture Introduction

Iridescent sharks are native to the vast and dynamic rivers of Southeast Asia, specifically the Chao Phraya and Mekong rivers. These mighty waterways provide the essential conditions for their survival, including ample food and appropriate breeding sites. However, due to their value in aquaculture, iridescent sharks have been introduced into other river systems across the globe. This expansion is driven by the high demand for their meat, which is a staple in many Asian diets.

The fish’s adaptability to various freshwater environments has facilitated their successful introduction into non-native rivers, where they are cultivated extensively. These introduced populations are managed in controlled environments to prevent ecological imbalance and to meet the market demand for their meat. The careful management of these aquaculture systems ensures a steady supply of iridescent sharks while minimizing the impact on local ecosystems.

Preferred Environmental Conditions

As freshwater fish, iridescent sharks thrive in tropical climates where water conditions closely mimic those of their native habitats. They prefer water with a pH range of 6.5 to 7.5, indicating a slightly acidic to neutral environment. The water hardness should be between 2.0 and 2.9 dGH, which ensures the right balance of minerals essential for their health. Additionally, they are most comfortable in water temperatures ranging from 22 to 26 degrees Celsius (72 to 79 degrees Fahrenheit).

These conditions are typical of the tropical rivers they inhabit, where the water is warm and stable throughout the year. Iridescent sharks favor large bodies of water, similar to the deep waters of the Mekong River basin, which provide them with the space needed for their extensive migrations and dynamic lifestyle.

Migratory Patterns and Behavior

The iridescent shark is a migratory species, with movement patterns closely tied to the seasonal changes in their river habitats. In most regions, these fish move upstream during the flood season when water levels are high, creating ideal conditions for spawning. This upstream migration allows them to reach spawning grounds that are otherwise inaccessible during lower water levels. Once the floodwaters recede, the fish return downstream to find suitable rearing habitats where they can feed and grow. The specific timing of these migrations varies depending on the river system.

In the Mekong River basin, iridescent sharks migrate upstream from May to July, coinciding with the onset of the rainy season, and move downstream from September to December as the water levels decrease. South of the Khone Falls, the upstream migration occurs from October to February, peaking in November and December. This timing is triggered by the receding waters at the end of the flood season, indicating the species’ finely tuned adaptation to their environment’s hydrological cycles.

Iridescent Sharks as Aquarium Pets

While juvenile iridescent sharks, or Pangasianodon hypophthalmus, are often sold as pets for home aquariums, they are not the easiest fish to care for. These fish can survive in a 40-gallon aquarium initially, but this is far from ideal for their long-term health and well-being. Iridescent sharks are schooling fish, meaning they thrive in groups and prefer the company of their own kind. Their natural habitat in large rivers involves extensive space to swim and engage in active behaviors. In captivity, they require significant space to accommodate their growth and schooling tendencies, making them unsuitable for most home aquariums.

Challenges of Keeping Iridescent Sharks

One of the significant challenges in keeping iridescent sharks is their poor eyesight. This condition causes them to perceive sudden movements outside their tank as threats, triggering their instinct to flee. When stressed, their first reaction is to dart away quickly, which can result in them colliding with the sides of the tank or other objects within it. These frantic movements can cause injuries, and it’s not uncommon for the fish to end up lying on their side or back at the bottom of the tank until they recover from the shock. The confined space of a typical home aquarium exacerbates these issues, increasing the likelihood of injury and stress.

Tank Requirements for Healthy Growth

For iridescent sharks to grow naturally and stay healthy, they need a significantly larger tank than what is typically available in most homes. Ideally, they require a tank size of at least 12 meters (39 feet) in length. This substantial space allows them to swim freely and exhibit their natural behaviors. When kept in schools, which is their preferred social structure, even larger tanks are necessary to provide adequate space for all individuals.

In the wild, iridescent sharks can grow up to 1 meter (3.3 feet) in length if given enough room and proper nutrition. However, in most home aquariums, the lack of space severely stunts their growth, with most individuals reaching only 15 to 30 centimeters (6 to 12 inches) before succumbing to the stresses of inadequate living conditions.

Considerations for Proper Husbandry

Proper husbandry is crucial for the well-being of iridescent sharks in captivity. When provided with adequately sized aquariums and appropriate care, these fish can thrive, growing to their full size and living into their teenage years. Adequate feeding, regular water changes, and maintaining the correct water parameters are essential aspects of their care.

Aquarists must also ensure the environment is free of sharp objects and has plenty of open space to minimize the risk of injury during the sharks’ frequent darting movements. Understanding the specific needs and behaviors of iridescent sharks is vital for anyone considering them as pets, emphasizing the importance of providing a habitat that closely resembles their natural riverine environment.

Albino Rainbow Shark: A Comparison

In contrast, the Albino Rainbow Shark, also known as the Albino Ruby Shark or Albino Red-Finned Shark, is more suitable for a semi-aggressive community aquarium. These fish can coexist with other species of similar size, as long as they are the only “sharks” in the tank. However, as they mature, Rainbow Sharks can become very aggressive toward their kind, necessitating careful management of their tank environment.

Unlike the iridescent shark, which requires a vast amount of space, the Rainbow Shark can be maintained in a typical home aquarium, provided its territorial nature is taken into account. This comparison highlights the importance of understanding the specific requirements and temperaments of different fish species to ensure a healthy and harmonious aquarium environment. Health books, guides, exercises, habits, Diets, and more

Growth Rate of Iridescent Sharks

The growth rate of an iridescent shark largely depends on factors such as diet, water quality, and tank size. With ample high-quality food and excellent water conditions, including regular water changes, these fish can grow rapidly. In optimal conditions, an iridescent shark can reach a size of 36 to 48 inches in as little as six months. However, it’s essential to bear in mind that these fish have the potential to grow much larger, eventually requiring tanks in the hundreds of gallons to accommodate their size. This rapid growth rate underscores the importance of providing the right environment and nutrition to support the healthy development of these magnificent creatures.

Handling and Feeding Guidelines

To ensure the well-being of an iridescent shark in captivity, it’s crucial to manage their diet and feeding routine carefully. A balanced diet is essential, consisting of high-quality flakes offered two or three times a day. It’s important not to overfeed them, as excess food can lead to water quality issues and health problems. Feed them only enough food that they can consume within five minutes to prevent waste and maintain water quality. Supplement their diet with live or frozen foods such as bloodworms or brine shrimp, which provide essential nutrients and help mimic their natural diet in the wild.

Compatibility and Tank Mates

When considering tank mates for iridescent sharks, it’s essential to choose peaceful fish of similar size. These sharks have a peaceful nature but can mistake smaller fish for prey, which could lead to aggressive behavior. Therefore, selecting tank mates that are not significantly smaller than the iridescent shark is crucial to prevent conflicts. Additionally, due to their shy and timid nature, aggressive fish should be avoided altogether. Creating a harmonious community tank requires careful consideration of the temperament and compatibility of each species to ensure a stress-free environment for all inhabitants. Fish and Fishing accessories


In conclusion, the growth rate of iridescent sharks can be rapid under optimal conditions, emphasizing the importance of proper care and management in captivity. Providing a balanced diet, suitable tank mates, and a spacious environment are essential factors in ensuring the well-being and longevity of these captivating fish. By following guidelines for feeding, handling, and tank compatibility, aquarists can create a thriving aquatic ecosystem that allows iridescent sharks to flourish and exhibit their natural behaviors in the confines of a home aquarium.

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