Molecular characterization of Clinostomum spp. infecting cultured Snakeskin gourami (Trichopodus pectoralis) in Thailand

The digeanean Clinostomum spp. is a significant parasitic pathogen of freshwater fish. It has low host specificity and a wide distribution geographically. Morphological and molecular data analyses have been performed on Clinostomum to assess its diversity. However, the molecular occurrence of Clinostomum spp. in aquaculture in Thailand has yet to be reported. Snakeskin gourami (Trichopodus pectoralis), a freshwater fish cultured in Thailand, has significant economic importance. Herein, the study focuses on describing a digenean Clinostomum in the abdominal cavity of T. pectoralis and reports the prevalence of this parasite from central Thailand. Two hundred and sixty-two 4 to 8- month-old T. pectoralis were obtained from Samut Sakorn, Samut Songkhram, Samut Prakarn, and Kanchanaburi provinces of central Thailand. We measured their overall length as well as their body weight. The body cavity of T. pectoralis was examined, and metacercariae of C. piscidium were discovered inside. In the abdominal cavity of infected fish, the parasites were discovered either free or adhered to adipose tissue and the outer membrane of the visceral organs. It was found that the total prevalence was 13.35 %, and the parasite intensities were found to be higher in the females taken from the farms than in the males (P<0.05). Pathological examination showed a few white migratory patterns on liver and spleen cells. The track presented histologically as the main central hepatic necrosis and hemorrhage surrounded by layers of macrophages and epithelioid cells. This metacercaria infection caused damage to the fish hosts' hepatic tissue, which disrupted their hepatic metabolism. As a result, the fish hosts experienced a slowdown in their rate of development and a reduction in their total body mass. In addition, morphological and molecular characterization of species was conducted using 18S rDNA and inter-transcribed spacer (ITS1 and ITS2) sequence data. A BLAST search of 18S rDNA sequence revealed 100% sequence similarity with C. piscidium (FJ970655) infecting banded gourami (Colisa fasciata) from India and 90–98% sequence similarity with other clinostomid in Australia, USA, China, Israel, and Italy. ITS sequence data also revealed 100% sequence homology with the C. pisicidium isolated from C. fasciata from India. Based on phylogenetic analysis, this study reports the first molecular identification of C. piscidium species in cultured T. pectoralis in Thailand.