Discarded from aquariums, exotic South American fish invades Noyyal tanks in Coimbatore

An exotic fish from South America that is commonly used as ‘cleaners’ in aquarium tanks is believed to be posing a threat to the aquatic biodiversity of wetlands linked to River Noyyal in Coimbatore.

Fishermen, whose daily earnings depend on fresh catches from Periyakulam (Ukkadam Big Tank), say that there is a sharp rise in population of this fish, which are sold by aquarium dealers as ‘suckers’ or ‘janitor fish’ as they keep tanks clean. As per the accounts of fishermen, they live in large numbers in Periyakulam, along with other fishes, including Rohu, Catla, Mrigal, Tilapia and African catfish, out of which the last two are also exotic.

“We are seeing a significant rise in the numbers of sucker fish in the past two to three years. They appear to proliferate in good numbers in a short period. Around 10 to 15 kg of the total catch in certain days account for this fish, which nobody wants,” said a fisherman from Periyakulam.

Biologists opined that the species found in Periyakulam could be suckermouth armoured catfishes belonging to the Genus Pterygoplichthys. After examining images of carcasses from Periyakulam tank bund, they opined that the species could be Pterygoplichthys disjunctivus or Pterygoplichthys pardalis.

Another fisherman said that this fish, with rigid body and sharp spines on dorsal and pectoral fins, get entangled in nets and it is a tough task to remove them. Nets also get damaged while struggling to remove them.

“This fish has become a menace for fishermen as it has spread rapidly in tanks here. Though we pooled in money and released fish fry in large numbers in Periyakulam, the yield was not as expected. We are not sure whether the poor yield has anything to do with the proliferation of suckerfish,” said P. Kannan, who heads 136 fishermen who catch fishes from Periyakulam and Valankulam.

According to fishermen, this invasive fish had previously been found in Valankulam in the city, another tank in the Noyyal river system. They say that fishermen from other tanks in Coimbatore have also reported the presence of this exotic fish.

S. Raja, Assistant Professor with the Department of Zoology at Kongunadu Arts and Science College, said the spread of these exotic fish in native waterbodies was getting reported from different parts of the country. He, along with Assistant Professors V. Veena and G. Sasikala from the Department of Zoology at PSGR Krishnammal College for Women, had earlier published a paper on the occurrence of Pterygoplichthys pardalis in Gayathripuzha, a tributary of the Bharathapuzha, in Palakkad district in Kerala.