A suckermouth catfish, native to South America’s Amazon River, was found in the Ganga River at Ramnagar, Varanasi district, in the state of Uttar Pradesh in northern India, by fishermen on Sept. 26.

It is the second time that fish species was spotted there in September.

Researchers at Banaras Hindu University examined the full-grown live fish and confirmed it to be Hypostomus plecostomus, found in the Amazon.

“Though we cannot confirm how the fish ended up in the Ganga, we believe aquarists would have let this into the water body,” said Bechan Lal, a zoology professor at Banaras Hindu University who examined the fish.

In addition to Uttar Pradesh in the north, the states of Bihar and West Bengal, in the east; Tamil Nadu in the south; Andhra Pradesh, in the southeast; and Assam, in the northeast have reported sightings of suckermouth catfish in their waters since 2010.

On April 22 this year, Bishnupur, in the northeastern state of Manipur, reported a sighting of the fish for the first time. The fish have also been spotted in the Krishna and Godavari rivers.

suckermouth catfish
Suckermouth catfish discovered in Varanasi by fishermen on Sep 2. (Courtesy: Namami Gange.)

Lal said the suckermouth catfish is hardy, meaning it can survive in hostile conditions.

“The hardy nature has helped it sustain in the Gangetic ecosystem,” he said. “We don’t yet know the percentage of this particular fish in the Ganga, but if the numbers keep rising, they will start competing with local species for food, marine and reproductive space.”

Kuldeep K. Lal, director of ICAR-National Bureau of Fish Genetic Resources, said, “Omnivorous feeding, a hardy nature and the ability to tolerate the hypoxic conditions allow the suckermouth catfish to survive and prosper in areas where no other fish can.”

ICAR-NBFGR works on risk assessment of alien species, which are introduced in bodies of water for cultivation or trade.

“The fish can breathe air, therefore, can withstand low oxygen levels,” Kuldeep Lal said. “Since it can breed in stagnant water, there is a risk of its easy establishment. Also, its thick skin poses a low risk from predation. So once out in a water body where conditions are conducive, it can establish well and those established populations can further fan out.”

Data from the Centre for Agriculture and Bioscience International suggests a host of characteristics that make this fish “successful invaders”: They are covered in armored plates, possess broad environmental tolerances and the ability to colonize anthropogenically disturbed habitats, provide parental care through nest-building and egg-guarding, and have the ability to breathe air in hypoxic conditions.

These invasive catfish not only pose a threat to the survival of local species, but also harm the riverine ecosystem.

“The fish alters the substratum structure and riverbanks because of its browsing and digging habits,” said Kripal Datt Joshi, principal scientist at ICAR-NBFGR.

“This fish is fit only for aquariums,” said Bechan Lal. “They don’t have any food value. So if their numbers keep growing, fishermen will have to bear losses because they won’t find buyers for the suckerfish that gets caught in fishing nets.”

“Suckermouth catfish species are popular aquarium fish and preferred for cleaning inside walls of aquarium owing to its habit to feed on growing algae,” said Joshi.

Tourists take a boat ride in the Ganga near Varanasi, India. The degrading water quality of the river’s water has been a concern for green activists. (Courtesy: Aditya Prakash/Unsplash.)

The fish are also known to damage fishermen’s gear because of their unique body armor.

The sucker-like mouth of the fish allows it to feed, breathe and attach to the substrate through suction. Respiration and suction can function simultaneously. This makes them an ideal aquarium fish and sought-after ornamental fish. Referred to as plecostomus or pleco by aquarists, suckermouth catfish have been introduced to 17 countries in the Americas, Asia and Europe.

A research paper, “Occurrence of Ornamental Fishes: A Looming Danger for Inland Fish diversity of India,” by S. Sandilyan states that 27 ornamental species were reported in the inland wetlands of India by 2016. Of those, 15 had established a breeding population and had emerged as a threat to native species.

In the canals of Thiruvananthapuram in the southwestern state of Kerala, the native fish population has declined because of the invasion of pterygoplichthys or sailfin armored catfish, a cousin of the suckermouth catfish. The number of fish collected by the cast net ranged from 3 to 27 throughout the study period by Biju Kumar, a faculty member in Aquatic Biology and Fisheries at the University of Kerala, which indicates the dominant biomass of the species. The invasive fish consume the eggs of native species, which leads to the extinction of indigenous varieties.

As of 2018, of 3,535 species in India’s freshwater, brackish and marine waters, 14 percent, or 495, were found to be alien.

“Alien established species are mostly found in degraded waters as these are hardy in nature and can survive and flourish in diverse, polluted, altered, regulated, derelict water bodies,” said Joshi, scientist at ICAR-NBFGR.

“Such alien intrusions can be avoided by creating awareness among the public, hobbyists regarding the safeguarding of our valuable biodiversity. Maintaining regular environmental flow in rivers and reducing pollution load/eutrophication can mitigate the risk of establishing these invasive alien species,” Joshi said.

Ramnagar, where the suckermouth catfish was discovered in Varanasi, has small factories on both banks that discharge chemical effluent into the water.

“Heavy discharge of industrial effluents and increasing pollution over the years has lowered the population of fragile fish species in Varanasi,” said Rajesh Kumar Saroj, a former member of the Ganga Action Plan in Uttar Pradesh.

“The shutdown of industries due to lockdown had helped in achieving a cleaner Ganga at Varanasi. But now that the factories are reopening, we are going back to square one, therefore exposing the aquatic species to the same environmental dangers again.”

(Edited by Siddharthya Roy and Judy Isacoff.)

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