In a startling discovery last year, an Ichthyological survey documented the presence of Pterygoplichthys disjunctivus—a species of Sailfin Catfish native to the Amazon—in the Lohandra river of Eastern Nepal. Known for its hardiness and invasive potential, the species has already disrupted ecosystems in India and Bangladesh. Due to the significant ecological impact of Loricariids species, Bangladesh has imposed a ban on any species of the suckermouth catfish group. 

As a non-edible species, its presence in natural waters points towards potential source—pet trade. The record of this species has raised serious concerns among conservationists. “The numbers suggest they have already adapted to natural water bodies and monitoring is necessary to determine whether they have become fully invasive or not,” said Jash Hang Limbu, lead researcher of the study.

The aquarium trade link

The Loricariids species, including Pterygoplichthys and Hypostomus, are popular aquarium fish for their ability to clean aquaria by feeding on algae. Sold as “plecos” or “sucker fish”, they are easily available in aquarium stores across the country. When small, they remain mostly at the bottom of aquariums, feeding on algae and detritus. However, these species can escape or are released into natural waters, once they outgrow aquariums. They have the capacity to adapt, which can result in disruption of native aquatic biodiversity. 

While the precise route of introduction into the Lohandra River remains unclear, researchers suspect a combination of accidental releases from aquariums and migration from Indian rivers as a potential cause.

Back in 2018, a specimen was recorded at a commercial fish farm in Dhanushadham municipality, and was released into Dhanush pond, a natural pond within Dhanushadham protected forest. “We failed to identify the species. However, it had an eye-catching body structure, so we rescued and released it in the pond,” said Dev Narayan Mandal of Mithila Wildlife Trust. 

Recently, two additional sightings were reported, both in commercial fish farms from the same locality. Despite the potential risk of invasion, the fish was released into nearby rivers. “To my information one farmer killed the fish but the other released it in a nearby river,” said Mandal. 

The presence of these fish in remote villages far from aquarium shops hints at the possibility of alternative introduction pathways, such as migration from India or accidental release via fish stock imports. In 2024, a specimen was also captured from the Narayani irrigation canal in Bara district. 

According to Limbu sailfin catfish have been recorded in irrigation canals and other water bodies in Morang and Jhapa districts in recent surveys as well. He suspects the presence of two species of sailfin catfish (Pterygoplichthys disjunctivus and Pterygoplichthys pardali) in eastern Nepal, although taxonomical identification is difficult.

In both India and Bangladesh—where the fish has invaded ecosystems, the primary source of introduction is the aquarium trade. Limbu suspects that the fish might have migrated from India through inter-connected river systems. As Nepal’s rivers are linked to those in India, the possibility can’t be dismissed. 

However, experts like Kripal Datt Joshi, retired principal scientist at Indian Council of Agricultural Research, are sceptical of the migration theory. “Nepal’s rivers are less polluted and fast flowing - conditions that are not congenial for this species,” he said. 

Likewise, Loricariids (both Pterygoplichthys and Hypostomus) are known for their ability to breathe air and even show terrestrial locomotion. Experts say considering this adaptive behaviour, the fish may have found alternative dispersal methods.

Growing threat of invasion in Nepal

The pet fish trade is not the only pathway for exotic invasive species in Nepal. Despite the tremendous native fish diversity - 236 indigenous fish species, introduction of exotic fish species started during the 1950s. A 2015 study by Prem Budha, Professor of Zoology, Tribhuvan University, documented 19 exotic fish species in Nepal. However, the list doesn’t include fish species reared in aquariums. 

Many were introduced for aquaculture without proper risk assessments. “If such exotic species escape or are released to natural ecosystems they might adapt to the environment, breed, and can become invasive,” said Budha. Species like Tilapia, has already outcompeted native fish in lakes of Pokhara. Recently, rainbow trout—a species listed under “100 of the World's Worst Invasive Alien Species”—has escaped and are recorded in natural waters, said Bharat Babu Shrestha, professor at Tribhuvan University. “It’s time to regulate exotic species, including Tilapia,” said Professor Shrestha.

Ornamental fish industry in Nepal

Nepal’s ornamental fish industry has grown rapidly, with aquarium shops flourishing in Kathmandu, Pokhara and other major cities. “The number of people buying fish has increased in recent years,” said the owner of Hobby Aquarium, one of Nepal’s oldest shops. 

However, the customs import data depicts a different story, showing a sharp decline in ornamental fish imports—an ironic contrast to the booming domestic market. 

Currently, imports are processed through the Nepal National Single Window (NNSW), where importers must list species name and quantities. “Based on that online application, import permissions are granted,” said Sumitra Laudari, Senior Fisheries Development Officer at Central Fisheries Promotion and Conservation Center (CFPCC).

Aquarium owners reported that importers import fish based on market demand and international availability. Most imports come from India and Thailand, with occasional imports from China, Indonesia, and other east-Asia-pacific countries.

Nepal lacks comprehensive research and a centralized database on aquarium fish imports. Limited studies exist, mostly in Kathmandu and Pokhara. A 2024 study published in International Journal of Biological Innovations journal reported 53 exotic and four native ornamental fish species sold in Kathmandu aquarium shops. Arowana was the most expensive, while Guppy the cheapest.  

Professor Budha noted that international trade is a major pathway for invasive alien species globally. “With growing demand, more non-native species are imported, increasing risk of introduction into ecosystems,” he added.

Another concern is “fish liberation”—religious practice where believers release captive live fish into water bodies.  “With exotic fish easily available, there’s a high chance non-native species are being released,” added Professor Shrestha.

Weak regulations, invasion risk and conservation concerns

The Nepal Fish Fry Standard 2061 (amended in 2077) lists 144 ornamental fish species allowed for import. However, many unlisted and high-risk exotic species such as Arapaima, Alligator Gar, Redtail Catfish, Pacu, Iridescent Sharks, Giant Snakehead, Red Devil and Peacock Bass are openly sold in the market. Known for their predatory behaviour and rapid growth, these species have caused severe ecological damage in other countries after escaping captivity. 

The aquarium trade also threatens conservation efforts. Some IUCN Red List endangered species like Reticulated Hillstream Loach and Bala Shark (Vulnerable) and Red-Tailed Black Shark (Critically Endangered) are easily available in the market, though they are not listed under the Nepal Fish Fry Standard 2061. 

 

Some of these are smuggled from India, often hidden among frozen fish shipments. “The mortality rate is high with such fish, so we avoid purchasing from those sources,” said a Kathmandu-based shop owner. Nepal’s open border and weak import inspection further increases the possibility of such illegal imports. 

Officials acknowledge enforcement challenges, citing a lack of technical officers at quarantine checkpoints. “Due to the lack of fishery experts at quarantine centres/posts, these fish species are often not identified correctly,” said Laudari. Ashok Adhikari from the Ministry of Agriculture and Livestock echoed a similar challenge, “Veterinary officers manage quarantine posts, but they often lack the expertise to identify fish species”.

A potential solution: Breeding native ornamental fish

Nepal has significant potential to develop a local ornamental fish industry. The CFPCC and Pokhara’s Fishery Research Station have begun breeding programs.

Though 15 native species with ornamental potential have been identified, only one is currently being bred. “Identifying and developing technologies for breeding native fish species for aquariums could be an important step in reducing import dependency” said Md Akbal Husen, Senior Scientist at Pokhara’s Fishery Research Station. For instance, River stone carp (Psilorhynchus sucatio)—a native algae eater known as “sucatio”, is being imported despite its local presence. Such species, if bred domestically, could serve as an alternative to invasive plecos or sucker fish. 

While the domestic production has increased slightly over the past five years, it still doesn’t meet the market demand, said Husen. According to Laudari, efforts are underway to expand breeding programs at CFPCC. 

Officials also reported even private breeders are starting to breed exotic species, but their operations remain unregulated.

The way forward

As the spread of invasive exotic fish species accelerates, Nepal must take proactive measures. Nepal has also adopted Kunming Montreal Global Biodiversity Framework (GBF), Target 6 of which aims to reduce the rate of introduction and establishment of invasive alien species by 50 percent, and to reduce/mitigate the impacts of invasive alien species on biodiversity and in ecosystem services. Nepal is currently drafting the National Biodiversity Strategy Action Plan (NBSAP)—a document that translates the global targets into national actions.

The approval of Invasive Alien Species Management Strategy and Implementation Plan 2081 has raised new hope. “This now provides us with a regulatory foundation,” said Professor Shrestha who was involved in drafting the strategy. “Conducting thorough risk assessment—both pre-border and post-border, is crucial in mitigating the risk of invasion” added Professor Shrestha.  

“Strengthening technical capacity at quarantine checkpoints is also essential to prevent the entry of invasive exotic species”, emphasized Professor Budha.