The Bangkok Metropolitan Administration (BMA) is working to curb the population of blackchin tilapia, which is increasing in three Bangkok districts.

The invasive species is causing trouble for farmers as it preys on smaller fish.

Bangkok governor Chadchart Sittipunt said the fish had been spreading from nearby Samut Songkhram provinces to other areas for some time, with numbers growing in three districts in Bangkok: Bang Khunthian, Thung Kru and Bang Bon.

About 900 farmers run shrimp and fish farms in the districts.

“The blackchin tilapia’s population is increasing rapidly, and they eat smaller fish and roe and can endure harsh environments, which makes them a threat to fish farmers,” Mr Chadchart said after a recent visit to Bang Khunthian.

The Department of Fisheries has measures to deal with the situation, including releasing predator fish into the waters.

Two thousand blackchin tilapia were originally imported from Ghana in 2010 by CP Foods, according to Isra News Agency. The company had a permit to study the fish for breeding at its research centre in Samut Songkhram province.

The company told the fisheries department that the fish had died within three weeks of being brought to Thailand and had been buried. But they later started showing up in local waterways and as their population grew, native fish species started decreasing in number.