Genetic Study Reveals Multiple Introductions and Human-Mediated Spread of Invasive Blackchin Tilapia in Thailand

Based on genetic analysis of 466 fish samples collected nationwide, the study identified high genetic diversity, including 19 distinct haplotypes, revealing that the species originated from multiple introduction events rather than a single release. The findings also show that subsequent human-mediated translocations within Thailand played a major role in the species' rapid spread.

The study represents one of the most comprehensive genetic assessments of blackchin tilapia in Thailand to date. Researchers confirmed that the invasive populations belong to Sarotherodon melanotheron melanotheron subspecies and identified 13 private haplotypes unique to specific populations. Several of these occurred at relatively high frequencies in Samut Songkhram, Prachuap Khiri Khan and Surat Thani, indicating multiple introduction sources and limited mixing among some regional populations.

Using haplotype distribution patterns, network analysis and phylogenetic comparisons, the researchers traced the origins of Thailand's blackchin tilapia to multiple geographic sources, including Ghana and Côte d'Ivoire, as well as potentially other unsampled native populations in West Africa.

The study also found that blackchin tilapia populations in different parts of Thailand are genetically distinct, particularly in Samut Songkhram, which is believed to be the earliest site of the invasion. At the same time, researchers discovered that fish sharing the most common genetic signature were found in provinces across eastern and southern Thailand, including Chachoengsao, Rayong, Chanthaburi, Chumphon, Nakhon Si Thammarat and Songkhla, suggesting they were transported by human activities rather than spreading naturally through connected waterways.

The researchers said "The findings provide valuable scientific evidence for strengthening surveillance and management of the invasive species. By identifying introduction pathways and patterns of dispersal, the study offers important guidance for preventing further spread, improving biosecurity measures and mitigating ecological impacts on Thailand's freshwater ecosystems."

Link to the research paper https://www.sciencedirect.com/science/article/pii/S2352513426002152

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