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Monstrous alien fish spotted in the rivers of Kerala after the state’s floods

Monstrous alien fish spotted in the rivers of Kerala after the state’s floods

Monstrous alien fish spotted in the rivers of Kerala after the state’s floods


Mangloretoday.com/ yahoo news

It was 7 September, barely a month after the floods of 2018 had wrecked large parts of Kerala. Though life was far from normal in Thrissur’s coastal Kodungalloor, 48-year-old Jaison Kallarackal was at his Chinese fishing net at dusk to land the day’s catch. As he began to haul the net up, he realised that it was unusually heavy; something large was wriggling in the net, causing it to shake. When a final heave raised the net slightly above water, Kallarackal could not believe his eyes.

Squirming around at the base was a fish he had never seen before: flat-headed and sporting large scales tinted in pink and cream. It measured six feet long and weighed a whopping 41 kilograms.

WhatsApp photographs of the unusual fish brought Smrithy Raj, a doctoral researcher studying fishes at Thiruvananthapuram’s >University of Kerala, to the spot in a couple of days. But all he saw of the fish was its severed head: it had already been sold in the market. His journey, however, was not in vain; he was able to procure a small piece of fish tissue from the head.  Genetic tests revealed that it was the arapaima, one of the world’s largest freshwater fish, endemic to the Amazon in South America.

Giant-fish-ker...


A man displays an alligator gar caught from a river in Kerala. The fish can measure up to three metres in length and could put the native fish species at risk. Image credit: Smrithy Raj.

After a month’s such work of analysing news reports, social media photographs and videos of ’strange’ fish caught after the 2018 floods, and re-confirming sightings with local fishermen and fish vendors, the team €" of A. Biju Kumar (University of Kerala), Raj, C.P. Arjun (of Thiruvananthapuram’s >Indian Institute of Information Technology and Management) and Unmesh Katwate and Rajeev Raghavan (of Kochi’s >Kerala University of Fisheries and Ocean Studies €" KUFOS) €" also obtained information on the presence of the alligator gar, another fish never recorded in Kerala’s waters before. Like the arapaima, the gar too is alien: its native habitats are the freshwater lakes of North America.

These post-flood field surveys revealed that fishers had caught arapaima and gar from four flood-affected rivers in Kerala: the Periyar, Muvattupuzha, Kurumali and Chalakkudy. The presence of these alien fish €" which are being farmed illegally in the state €" could bode ill for Kerala’s native fish diversity, claim the scientists. In their >communication in the journal Current Science in May this year, the team call for an urgent nationwide scheme to eradicate such alien fish species.

 

Giant-fish-ker...


Kerala’s flood ’fugitives’

Kerala’s river systems, which the authors study, are home to around 200 species of fish, 30 percent of which are endemic to the region. But this diversity is at risk due to ’fugitive’ fish such as the arapaima and gar that escaped from aquaculture facilities and farms during the floods, claim the authors. Calling the 2018 floods one of the most "significant threats" to Kerala’s fish diversity, the team adds that the presence of alien arapaima (Arapaima gigas) and alligator gar (Atractosteus spatula) here is a serious concern for several reasons.


Giant-fish-ker...


Both alien species can grow to be enormous. While alligator gar can measure up to three metres in length, arapaima is five metres long and weigh up to a whopping 200 kg. Both species are also top predators in their native habitats, feeding on smaller fish (which puts Kerala’s small native species at risk). The arapaima and gar are dedicated parents too: their active care of their young increases the survival of their broods.

Additionally, arapaimas are air-breathers, a feature that could help them survive even in polluted habitats. Their large scales are tough for predators to break through. Arapaima introductions in some American countries have caused a decline in native species, which in turn has affected local fisher livelihoods. Alligator gar too are formidable predators; they are piscivorous generalists with an affinity towards live fish, said Raghavan, an assistant professor at KUFOS. "This species could have a bigger chance to proliferate in Kerala’s freshwater habitats than the arapaima," he says.


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Are fugitives always foes?

However, there are no studies on the actual impacts these species could have on freshwater systems in India. And the team recorded only six arapaima and gar in total: a number that seems barely enough to ’threaten’ river systems.

The Chinese fishing net in Kodungalloor, Kerala, where Jaison Kallarackal caught the arapaima. The fish probably escaped from aquaculture facilities during the floods, and are now ’fugitives’ in the natural ecosystem, claim researchers. Image credit: Smrithy Raj.

Other invasives include the guppy and mosquitofish (legally introduced to control mosquito populations). ’Tankbusters’ €" fish that are capable of outgrowing most domestic aquaria €" are a problem too. Kumar, who documented how ornamental exotic South American suckermouth armoured catfishes (genus Pterygoplichthys) were invading the drain networks of Thiruvananthapuram city in a study in 2015, found that traders and aquarium hobbyists were releasing these fish into drains when they grew too large for their aquariums or tanks.

Similarly, there is a huge demand for arapaima and alligator gar among fish hobbyists but these fish quickly outgrow their aquariums and owners often release these fish in the wild, said Raghavan.


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