Dr. Thon Explains Three-Phase Timeline of Black-Chin Tilapia Invasion at Pattaya Beach, Calls Eradication Difficult as Dangerous Alien Species
Invasive black-chin tilapia are spreading rapidly from coastal canals to Thailand's open waters in three phases, with experts warning that eradication is nearly impossible once the alien fish establish themselves in marine ecosystems.
On May 14, Dr. Thon Thomrongnawasasat, a marine and environmental scholar and vice dean of the Faculty of Fisheries at Kasetsart University, posted on Facebook detailing the mass appearance of black-chin tilapia at Pattaya Beach in Chonburi Province. He outlined a three-phase timeline across three zones showing how the invasive fish species spreads from coastal canals to open waters.
Phase One begins in coastal canals where black-chin tilapia, lacking natural predators, reproduce prolifically until canals are choked with fish. As they deplete food resources in cramped canal systems, adult fish migrate seaward in search of new habitats.
Phase Two involves the fish moving into nearshore areas and brackish-water bays like mangrove-lined coves. These semi-enclosed areas like Khung Krabaen provide suitable breeding grounds and marine ecosystem disruption, though the fish continue spawning in adjacent canals before juveniles venture into bays.
Phase Three encompasses open coastlines near canal mouths and mangrove forests. Black-chin tilapia sightings have been reported along Phetchaburi beaches for two years, with fishermen catching them. They now appear in semi-enclosed bays like Pattaya, where mature fish escape crowded freshwater sources to disrupt coastal ecosystems.
Dr. Thon predicts that coastlines matching Pattaya's characteristics throughout Thailand are already affected but unreported. The fish will continue expanding their range canal by canal, with mature individuals venturing to sea and establishing new populations in subsequent canals through reproduction and migration.
Eradication proves extremely difficult—even in confined canal areas, complete removal is impossible. In extensive coastal waters, efforts can only slow the impact through targeted fishing methods used by local fishermen: casting nets to catch schools, sun-drying for consumption or OTOP products, and destroying juveniles to prevent further spread, as they directly damage coastal ecosystems that support livelihoods.
Protection must focus on distant islands; while black-chin tilapia survive in seawater, crossing to islands like Kood, Tao, and Phangan remains unlikely. Prevention requires stopping intentional releases, with immediate action upon discovery to avoid transforming islands into affected zones like current coastlines.
Dr. Thon concludes that black-chin tilapia will gradually expand along coastlines from canal to beach, progressively spreading as this dangerous invasive species reaches epidemic proportions where eradication becomes impossible and only containment and island preservation remain viable.
Department of Marine Resources Director-General Pin Saksakul Surasudee stated he has ordered monitoring of the black-chin tilapia outbreak due to concerns about widespread damage. He classified the species as an Invasive Alien Species and said the department will coordinate with relevant agencies to investigate whether black-chin tilapia has spread to other locations.
