- The giant snakehead (Channa micropeltes), a predatory fish native to Southeast Asia, has been found in Sri Lanka’s Deduru Oya reservoir, raising concerns over the invasive species’ potential impact on native freshwater biodiversity and inland fisheries.
- With the ability to grow up to a meter (3 feet) in length, the giant snakehead is larger and more aggressive than Sri Lanka’s largest native snakehead species, posing a threat of outcompeting them and disrupting local aquatic ecosystems.
- Introduced through the aquarium trade, these snakeheads have already become invasive in countries such as the United States and Malaysia, triggering ecological crises that have led to bans, public awareness campaigns, and targeted removal programs.
- With more than 30 invasive fish species now established in Sri Lanka’s waterways, experts warn that weak enforcement and poor regulation over exotic fish imports and aquaculture practices are increasing the risk of further biological invasions.
COLOMBO — The Deduru Oya reservoir in northwestern Sri Lanka has long been a favorite fishing spot for angler Ishanka Dissanayaka. In mid-June, he returned to the reservoir for a relaxing day by the water. But this time, the fish that snagged his bait was so heavy that he had to wade to the edge of the water and, with the help of colleagues, hauled it out using a hand net. The fish measured nearly a meter (3 feet) in length and weighed 8 kilograms (17. 6 pounds), one of his heaviest catches to date. What made it even more remarkable was when it turned out to be giant snakehead (Channa micropeltes), one of the world’s most feared invasive freshwater fish, now clearly established in Sri Lanka.
While Dissanayaka saw the catch as a personal triumph, others in the community viewed this discovery with alarm.
Local fisher Vijith Samantha recalled how fishing near the banks during windy days used to yield a decent catch. But now, he said, those catches have been reduced by half, with many of the native species once commonly caught seeming to have disappeared.
Dramatic increase of giant snakeheads
Samantha attributed this dramatic change to the rise of the giant snakehead, an apex predator native to Southeast Asia. With a torpedo-shaped body and powerful jaws filled with sharp teeth, the snakehead can launch lightning attacks to prey on other fish, amphibians and even small birds.
According to Ramani Shirantha, a senior scientist at Sri Lanka’s National Aquatic Resources Research and Development Agency (NARA), this fish is capable of growing to a length of 1.3 m (4.3 ft) and weigh up to 20 kg (44 lbs). Its hunting prowess, coupled with its adaptability, makes it a major threat to native ecosystems.
The first confirmed sightings in Deduru Oya occurred in early 2024, with some fishers sharing photos of an unusual-looking fish on social media. But the fish may have been caught in nets before that, where it could have been mistaken for the native striped snakehead (Channa striata), a common species locally known as loola.
Subsequent expert assessments confirmed the presence of the giant snakehead and, more importantly, suggested that the fish were breeding. Specimens of varying sizes, from juveniles to full-grown adults, indicated an established, self-sustaining population.
Aquarium industry’s role
The likely origin of this invasion, according to Upali Liyanage of the National Aquaculture Development Authority (NAQDA), is the aquarium trade.
Juvenile giant snakeheads, with their striking stripes and reddish tint, are a favorite among “monster fish” enthusiasts. But as they quickly outgrow home aquariums, many owners resort to releasing them into larger water bodies, often unaware of the long-term ecological consequences. While floods can also lead to accidental releases from outdoor tanks, experts say deliberate, albeit uninformed, releases are the more probable cause of the introduction at Deduru Oya.
The giant snakehead’s biology is uniquely suited for invasion. It’s an obligate air-breather, meaning it must gulp air to survive, allowing it to thrive in low-oxygen or stagnant waters where other species can’t easily survive. It can even survive short periods out of water and move across land to reach new habitats. During breeding, a single female can lay between 2,000 and 10,000 eggs in multiple batches each season, and both parents aggressively guard their young, increasing the survival chances of young fish. These traits give the species a distinct edge in new environments.
According to fisher Samantha, the number of giant snakeheads seemed to increase noticeably following a severe dry spell that drastically lowered the reservoir’s water level. He said he believes that while many other fish perished, the snakeheads survived by burrowing into pockets of mud, allowing their population to grow rapidly once water levels rose again.
Capacity to survive the odds
The giant snakehead is globally notorious as an invasive species. Native to the Mekong and Chao Phraya River basins in Southeast Asia, it has already invaded freshwater systems in Malaysia, Indonesia, the Philippines, parts of India, and even the United States.
In each instance, its introduction has caused significant ecological disruption. In the U.S., the closely related northern snakehead (Channa argus) is creating similar disruptions in a number of states. U.S. authorities first recorded it in 2002, and responded through emergency measures, including possession bans, electrofishing efforts, and public awareness campaigns. The fish’s uncanny ability to survive on land earned it the nickname “Frankenfish.”
Sri Lanka now faces a similar threat. The country’s freshwater ecosystems are rich in biodiversity, with more than 50 endemic freshwater fish species, many of them found only in isolated river basins or mountain streams. Among Sri Lanka’s native snakeheads are the loola, the Ceylon snakehead (Channa orientalis), dwarf snakehead (Channa gachua), bull’s-eye snakehead (Channa marulius), the endemic Channa kelaartii, and the gan ara (Channa ara) —long the most dominant freshwater predator in the country, but potentially overshadowed by the bigger, faster-growing, more aggressive giant snakehead.
Ecological threat with economic impact
The ecological threat posed by the species also carries economic consequences. Freshwater fishers rely on predictable seasonal catches of commercially valuable species like loola and tilapia.
If the giant snakehead comes to dominate the food web, it could drastically reduce the availability of these fish, undermining both biodiversity and livelihoods, Liyanage said. The current invasion trend is further complicated by the lack of regulation and monitoring of Sri Lanka’s freshwater aquaculture sector. Biosecurity enforcement — the monitoring of animal and plant species imported into the country — has long been a weak point, leaving Sri Lanka vulnerable to such biological invasions, according to scientists.
In other countries where the giant snakehead has become established, such as Malaysia and Thailand, governments have promoted commercial harvesting of the fish to keep populations in check. In Sri Lanka, fishers sometimes eat it, but most people are still hesitant; to promote their consumption, the NARA team, cooked and ate giant snakehead during an inspection tour.
According to Sri Lanka’s National Red List of freshwater fish, as many as 30 fish species have been identified as invasive in the country. While species like Mozambique tilapia (Oreochromis mossambicus) were intentionally introduced for aquaculture, most others, such as the knifefish (Chitala ornata, native to Southeast Asia), alligator gar (Atractosteus spatula, from North America), tinfoil barb (Barbonymus schwanenfeldii, from Southeast Asia) and the so-called tank cleaners or suckermouth catfish (Pterygoplichthys spp. , from South America) have been released from aquariums.
Lack of public awareness and policies
Despite the growing threat, Sri Lanka still lacks public awareness, targeted policies and early monitoring mechanisms to prevent further spread of invasive species like the giant snakehead. Shirantha from the aquatic research agency emphasized the urgent need for action, including discouraging exotic pet fish releases, enforcing stricter regulations on fish imports, and offering incentives for harvesting and consuming invasive species to help manage their populations.
The Deduru Oya reservoir is part of a broader network of waterways, with tributaries and canals connecting it to other water bodies. Without swift intervention, the giant snakehead could spread farther, endangering more of Sri Lanka’s freshwater ecosystems, observers warn. The situation at Deduru Oya is more than a localized crisis, they say, and represents a stark warning about the country’s vulnerability to invasive species, its regulatory shortcomings, and the silent transformations reshaping its aquatic landscapes.
Banner image: Giant snakeheads are thought to have been introduced to the Deduru Oya reservoir about three years ago, and since then more than three generations of the species have spread throughout the water body, scientists say. Image courtesy of NARA.
