The alien invasion had been menacing Thailand for some time.
But it wasn’t until countless blackchin tilapia were spotted floating in a drainage pond beneath a Bangkok tollway on Monday that the public woke up to the threat.
The fish died as a result of a sudden change in water level, which was lowered by authorities to prevent flooding ahead of expected downpours.
When locals examined their nets after scooping up the dead fish, they saw that blackchin tilapia accounted for most of the catch.
“We never knew that there were blackchin tilapia in the area,” said Koranit Buachan, director of Ratchathewi District Office.
“Now, we have to make plans to control and eradicate [the invasive fish].”
Aliens with an appetite for destruction
Native to West Africa, blackchin tilapia (Sarotherodon melanotheron), known in Thailand as Pla Mor Kang Dam, breed rapidly.
According to natural history portal Animal Diversity Web, they generally breed every 22 days, with females producing anywhere from 200 to 900 eggs that are incubated by the males.
Blackchin tilapia are also notorious as voracious predators.
They prey on other fish and have been known to decimate local wildlife, upsetting the delicate ecological balance.
They also wreak havoc on commercial stocks in fish and shrimp farms, hoovering up fry and roe.
Thai shrimp farmers and coastal fishermen have complained about invasive blackchin tilapia for years.
Able to withstand high levels of salinity, this alien species thrives in not only freshwater but also brackish and salty environments.
The threat is considered so serious that the Ministry of Agriculture and Cooperatives banned the import, export, transport, and farming of Sarotherodon melanotheron in 2018.
Exemptions are made only in special cases, with permission from the Fisheries Department’s director-general.
Anyone convicted of farming this species faces a fine of up to one million baht and/or one year in jail.
The same punishment applies to anyone who releases blackchin tilapia into natural waterways.
For repeat offenders, the maximum penalties are doubled.
How did the invaders arrive?
It remains unclear how invasive blackchin tilapia were first released into waterways across Thailand. Charoen Pokphand Foods (CPF) imported around 2,000 specimens of the alien species from Ghana to its facilities in Samut Songkhram in December 2010 as part of breeding research to improve the quality of Nile tilapia.
CPF insists that all the imported fish were disposed off properly after research concluded the blackchin tilapia offered no prospect of breeding improvements.
But in 2012 they began showing up in Samut Songkhram waterways.
The Fisheries Department says DNA tests confirmed that the invasive fish in Thailand come from the same parent stock.
By 2016, blackchin tilapia had infested multiple provinces at the expense of native species and the ecosystem.
A 2017 survey estimated that about 30 million specimens of the invasive predator were loose in Samut Songkhram’s shrimp-farming areas.
The financial damage to the farms was estimated at between 150 and 350 million baht.
Authorities say blackchin tilapia have now invaded at least 13 provinces and are spreading fast.
What’s next?
The Assembly of NGOs for the Protection and Conservation of Environment and Natural Resources has called for efforts to track down the culprits and make them pay for the damage that blackchin tilapia have caused to Thai biodiversity and aquaculture.
CPF denies causing the infestation.
The food giant has also vowed to support government efforts to contain the destructive invasion. These include the Fisheries Department’s plan to buy blackchin tilapia caught in Thai waterways and grind them up for use as animal feed or fertiliser, and to release other predator fish into waterways to eat the invasive species.
By Thai PBS World’s General Desk
