Aquarium fish invading waterbodies, ecosystems

T. Nandakumar
Thiruvananthapuram,  
The Hindu, April 4, 2015

The suckerfish, a popular aquarium species native to South America, is invading waterbodies in Kerala and posing a threat to native fishes and ecosystems, a study conducted by the University of Kerala and Rajiv Gandhi Centre for Biotechnology (RGCB) has revealed.

The study by Biju Kumar and Smrithy Raj of the university Department of Aquatic Biology and Fisheries and Sanil George and Sureshkumar of RGCB recorded the abundance of the exotic species in the Amayizhanjanthodu, one of the major drainage channels in Thiruvananthapuram city.

Hybridisation

But despite employing modern methods such as DNA barcoding and mitochondrial gene sequencing, the team failed to establish the identity of the species, leading to the inference of hybridisation.

Also known as Janitor fish or sailfin armoured catfish, the suckerfish (scientific name Pterygoplichthys ) is popularly reared in aquarium tanks across the world to clean the glass plates of algae. With large dorsal fins and rows of armour plating on the body, it is adapted to survive without water for more than a day.

Due to their ability to tolerate poor oxygen content in water and the absence of natural predators, armoured catfishes have established natural populations across India and Europe as well as the U.S., Mexico, Japan, Malaysia, Singapore, the Philippines, Sri Lanka, and Bangladesh. As a resilient species, invasive suckerfish are known to outcompete native species of fish, drive them away, and consume their eggs.

As bottom feeding species, they also uproot and change the composition of aquatic vegetation.

Threat threshold

“The possibility of hybridisation raises the threshold level of the threat,” says Dr. Kumar. Hybrids are considered more virulent invaders and in countries such as the U.S., they are termed nuisance species due to the extensive damage caused to ecosystems and biodiversity.

A survey conducted by the researchers later revealed that ornamental fish traders and aquarium enthusiasts in the city were releasing the fish into drainage channels after they grew too big for the tanks.

According to the findings published in the Journal of Threatened Taxa , an open access publication, the suckerfish has invaded the Veli lake, Karamana river, and Vellayani lake in Thiruvananthapuram and has also been reported from many other water bodies across Kerala.

Pointing to the difficulties in controlling invasive species, Dr. Kumar calls for legislation to prevent the release of ornamental fishes and potentially damaging cultivable alien species into natural water bodies.

He proposes a programme to return unwanted species to aquarium traders under the precautionary principle.

“It is high time a campaign was taken up to highlight the ecological implications of this species to students, aquarium hobbyists, and fish breeders.”