Occurrence of Parasitic and Bacterial Pathogen in Ornamental and Wild Populations of Siamese Fighting Fish (Betta splendens) in a Region of Thailand

The diversity of fish parasites reflects the diversity of parasites in the water source, providing insights into the effects of pathogens and essential information about parasite-host relationships. Parasitic infections are valuable indicators of the aquatic ecosystem, influenced by various factors. This study aimed to investigate the prevalence and seasonality of parasite species and pathogenic bacteria in Siamese fighting fish (Betta splendens) over 12 months, involving sixty ornamental Siamese fighting fish collected from commercial sources and 81 wild Siamese fighting fish from different natural habitats. Parasite prevalence in ornamental Siamese fighting fish (25.00%) was lower than in the wild (34.57%). The protozoa parasite Trichodina was found in both Siamese fighting fish, with the highest prevalence recorded for Trichodina sp. in wild Siamese fighting fish. The winter season exhibited the highest parasitic prevalence, with a tremendous diversity of parasites found at each location, followed by the rainy and summer seasons. This study also reported the first finding of Henneguya sp. infection in Siamese fighting fish and on the body surface. The prevalence and seasonality of parasite genera were significant in the wild compared to ornamental Siamese fighting fish. Bacterial isolation was performed on internal organs, and isolates were identified using PCR techniques. Aeromonas veronii and Mycobacterium marinum were detected in ornamental Siamese fighting fish, while A. veronii was found in wild Siamese fighting fish. These findings indicate that infections in Siamese fighting fish display seasonal variation and are impacted by their ecology. This information is fundamental for managing the biodiversity of parasites in fish and preventing parasite infections in aquaculture.