The fish nobody wants is taking over Dhaka’s rivers

Near Sadarghat on the Buriganga, Kamal Miah bent over a fishing net on his boat's floor. A few kilos of sucker fish were stuck in it. He pulled them out one by one, carefully freeing their fins.

Beside him was a plastic bowl holding a few smaller fish. Those were the ones he hoped to sell.

"Look at the net. You would think we had a good catch," Kamal said. "But most of these fish will bring us nothing."

Around him, boats moved between the riverbank and the launches. Kamal kept working. Each fish had to be removed carefully. Pulling too hard could damage the net. Leaving them tangled would delay his next trip.

"We used to get sucker fish before, too. Now, sometimes I spend more time taking them out than sorting the fish I can sell," he said.

Across Dhaka, near Dhaka Uddan in Mohammadpur, Mohammad Selim faced a similar problem beside the Turag. His companion shook their catch out of a net while he picked through it, separating the saleable fish.

"The trouble is, we still have to do all the work," he said. "We take the boat out, cast the net and bring everything back. Then we sit here removing fish nobody wants."

"Three or four years ago, there were not so many sucker fish. Now, if we catch 20kg of fish a day, 15kg is sucker fish," Selim said.

When the sorting was finished, the larger pile contained sucker fish. The smaller pile would determine their earnings.

A catch that brings little income

Neither fisherman remembered a single day when the river suddenly changed. They described a slower process. First, an occasional sucker fish appeared in the net. Then several. Eventually, finding them became an ordinary part of fishing.

"Before, we would complain when a few came up," Selim said. "Now we look through them to find the other fish."

He picked up one caught near the edge of the net. Its body was covered in hard plates. A fin remained tangled in the thread.

"If I pull, the net tears. If I take it out carefully, it takes time," he said.

For Kamal, the work continued after the catch reached the bank. He still had to find a buyer for the fish worth selling. The time spent removing sucker fish added nothing to the value of his catch.

His expenses did not depend on whether the catch was useful. Equipment needed maintenance. Damaged mesh needed repairing. A poor day on the river still had to be followed by another fishing trip.

"People see fish in the boat and think we have earned a lot of money," he said. "They do not see what we throw away."

Kamal described the change through the contents of his net. Some catches looked promising until he began sorting them. On other days, he recognised the problem before the net was fully aboard.

Selim did not expect every trip to bring a good return. Fishing has always involved uncertainty. What troubled him was the growing amount of work spent handling a catch with little value.

"I can accept a bad day," he said. "But when the same thing keeps happening, you start wondering where to go."

Moving to another stretch of river could mean unfamiliar fishing grounds and more time travelling. There was also no guarantee that the next place would be different.

Their concerns show why the composition of a catch matters. A river can contain large quantities of fish while providing a poor living for fishermen. The species inside the net help determine whether a day's work pays.

Near Sadarghat, Kamal paused to examine a loose section of mesh. He ran his fingers along it before setting the net aside.

"I have to fix this before I use it again," he said.

Small repairs take time. More serious damage can make a net difficult to use. Handling sucker fish also brings the risk of injury. Their sharp spines can catch both the mesh and the hands trying to free them.

Selim said he worked slowly when several fish were tangled together.

"When we are tired, we want to finish quickly," he said. "That is when you have to be careful."

"The real concern is that sucker fish are spreading into healthier rivers, haors and beels, where they were not previously found. Their numbers are increasing rapidly, and I cannot imagine what the situation will look like in another 20 years. They may appear harmless, but they compete with native fish for food and living space. If this continues, they could seriously damage our freshwater ecosystems," Dr Md Niamul Naser, a professor at the Department of Zoology, University of Dhaka, told TBS.

"Consider a fisherman who catches 10kg of fish. If 8kg consists of sucker fish, only 2kg is left for him to sell. The rest have almost no commercial value. These fish also damage fishing nets and make the fishermen's work more difficult. We have very limited ways of using them commercially. Fishmeal production might be an option, but fish caught from heavily polluted rivers such as the Buriganga could pose contamination risks," he added.

From aquariums to Dhaka's rivers

Suckermouth catfish entered Bangladesh through the aquarium trade in the 1980s. Their suction-cup mouths and habit of feeding on algae made them popular as cleaner fish.

Inside an aquarium, they appeared useful. Released into open water, they could survive, reproduce and spread.

The problem extends beyond sucker fish. TBS previously reported that snake-skin gourami, locally known as "China kholisha", had become increasingly common in canals in Feni and Noakhali following floods. 

Researchers suspected that they had escaped from ornamental fish hatcheries in Feni. One fisherman, Shaheen, said his catches were now dominated by the species, leaving few other fish to sell. 

Professor Md Manjurul Kibria of the University of Chittagong warned that its rapid breeding and ability to survive in low-oxygen water could put native fish under growing pressure.

Floods are one route into open waters. Deliberate releases are another. Professor Kazi Ahsan Habib of Sher-e-Bangla Agricultural University told TBS that aquarium owners sometimes release foreign fish into natural water bodies when their tanks become overcrowded. Once released, these fish can reproduce and spread. 

Kibria called for stricter testing and quarantine of imported aquarium fish, warning that weak controls were allowing species such as sucker fish and gourami to spread. He also reported the presence of sucker fish in the Halda, an important natural breeding ground for native carp.

A 2023 study published in the Bangladesh Journal of Zoology, titled "Invasive Suckermouth Catfishes in Bangladesh Wetlands: Present Status and Challenges", identified 2008 as the year of the first confirmed record of the fish in Bangladesh's open waters.

Subsequent reports documented their presence in rivers, canals, lakes, haors, beels, ponds and paddy fields.

The study recorded sucker fish in at least 17 rivers. These included the Buriganga, Turag, Shitalakshya, Padma, Halda and Meghna.

The range of habitats helps explain why containing them is difficult. They can survive in flowing or stagnant water and tolerate polluted conditions and low oxygen levels. Their hard bodies provide protection, while their growth and breeding characteristics help populations become established.

Once they enter connected waterways, their spread is no longer confined to the original release point. Around Dhaka, a fish released into one water body can become part of a problem extending through a larger river system.

The Bangladesh Journal of Zoology study also examined media reports published between 2009 and 2023. It found a sharp rise in reported sightings after 2020, with reports peaking in 2022.

Sightings were concentrated around Dhaka, Chattogram and Khulna. The researchers identified releases associated with the aquarium trade as an important source of introduction around urban centres.

Those reports help trace the spread. They do not provide a direct count of fish in each river. Greater awareness and media attention can also increase the number of sightings recorded.

Another 2023 study, published in Asian Fisheries Science, reviewed the invasion, its impacts and management options. It reported sucker fish in 38 of Bangladesh's 64 districts.

Titled "A Review of Suckermouth Armoured Catfish Invasion, Impacts and Management: Is Its Invasion a Threat to Bangladesh's Fisheries Sector?", the paper drew on evidence from Bangladesh and other countries.

Together, the studies describe a problem extending well beyond isolated ponds or aquarium release sites. Repeated surveys at the same fishing grounds would help establish how quickly populations are changing.

New research has found that the fish commonly grouped under the name "sucker fish" include several species in the Buriganga. A study published in July 2026 in the Dhaka University Journal of Biological Sciences used DNA testing to identify three species among fish collected from the river.

Researchers examined 14 specimens caught at Aminbazar, Sadarghat and Fatulla in June 2025. Ten were identified as Pterygoplichthys disjunctivus, three as P. ambrosettii and one as P. pardalis. The authors describe their findings as the first molecular evidence of these three species coexisting in Bangladesh.

The findings suggest that the invasion may involve repeated introductions or releases of mixed aquarium stocks. However, the study did not establish exactly how the fish entered the river. The researchers called for wider surveys and further ecological research to understand their distribution and guide management.

A 2023 study published in Biological Invasions found that sucker fish had become firmly established through natural breeding in the Buriganga, Turag, Shitalakshya and Atrai rivers. The researchers interviewed 45 Buriganga fishermen, who estimated that sucker fish made up more than 98% of their catches outside the rainy season. 

From June to August, the share reportedly fell to around 90%. Researchers also carried out 31 cast-net samples in the Buriganga in March and April 2022. Every fish caught in those samples was a sucker fish, showing how heavily the species dominated catches at the surveyed locations.

The study also tested the effects on native fish in experimental ponds. Where sucker fish were stocked at high densities, mrigal was 48.4% lower and rohu (rui) growth was 21.4% lower than in ponds without them. Mrigal survival fell to 70%, compared with 100% in ponds free of sucker fish.

Fishermen increasingly find their nets filled with sucker fish, which offer little or no value.

Another pressure on polluted rivers

Dhaka's rivers were already under pressure before sucker fish became common.

Pollution had damaged habitats and reduced opportunities for native species. The arrival of a fish able to tolerate difficult conditions added another concern.

Selim remembered earlier complaints about the water and declining catches. Sucker fish became part of that conversation later.

"We were already struggling to find enough fish," he said. "Now we catch these too, but they do not solve anything."

Researchers have identified several ways sucker fish can affect freshwater ecosystems. They compete for food and space. Their nesting burrows can weaken riverbanks and contribute to erosion.

The Asian Fisheries Science review discussed evidence from other countries about their effects on fishing and native species. It described how established populations can alter habitats and become a substantial part of catches.

However, a decline in native fish cannot automatically be attributed to sucker fish alone. Pollution, damaged habitats and other pressures must also be considered.

These problems can interact. Degraded water can make survival harder for less tolerant native fish while allowing sucker fish to persist.

For fishermen, the result appears in the catch. There may still be fish in the river, but fewer of those caught may have a ready market.

A ban, but little relief

In early 2023, the Ministry of Fisheries and Livestock officially banned the import, breeding, sale, transport and possession of sucker fish by amending the Protection and Conservation of Fish Act, 1950. The Department of Fisheries is responsible for enforcing the ban, carrying out field-level crackdowns and monitoring markets alongside law enforcement agencies and mobile courts.

The restrictions address further introductions through trade. Controlling populations already breeding in open rivers is a more difficult task.

Speaking to TBS earlier this year, Dr Md Hasan Faruque, an associate professor in the Department of Fisheries at the University of Dhaka, warned that sucker fish had already spread across much of Bangladesh, making their control increasingly difficult. "Our research and field observations show that this invasive fish is now present in rivers, wetlands, canals, beels, haors, ponds and even paddy fields across much of the country," he said.

He also pointed to their movement through connected waterways, particularly around urban centres such as Dhaka.

Faruque said fishing communities were already suffering. Fishermen were finding their nets filled with sucker fish that had little or no market value, while native species such as koi, shing and punti were becoming scarcer. Torn nets, injuries and declining incomes were also affecting fishermen along rivers such as the Buriganga, he said.

"Banning import and trade was necessary, but it came too late," he said. Faruque called for a national action plan combining stricter enforcement, scientific monitoring, public awareness and financial incentives. He suggested that the government purchase sucker fish caught by fishermen and arrange for their safe disposal, including burial, as a way to reduce their populations and protect native species.

Such an arrangement would give fishermen a reason to remove fish that currently bring little income. It would require organised collection, payment and disposal, along with monitoring to assess whether removal was reducing the problem.

The research warned that complete eradication from large, open river systems would be extremely difficult. Reducing damage to habitats and livelihoods therefore becomes an important part of management.

For fishermen, the immediate question is what to do with the unwanted catch. Without a reliable market or an organised collection system, they must handle it themselves.

Selim gathered the saleable fish and passed them to his companion. The sucker fish still had to be dealt with. Then the net would need checking before they could leave again.

He was uncertain what another trip would bring. Staying ashore, however, would bring no catch at all.

Kamal faced the same decision near Sadarghat. He lifted the plastic bowl and looked at the fish inside. There were some to sell, though fewer than he had hoped.

He would take them to a buyer, return to the boat and finish repairing the net.

"Tomorrow we will go again," he said. "What else can we do?"