Trematode Infection Rates of Fish from a Wastewater Treatment Factory Polishing Pond and a Canal in Phuket, Thailand

The infection rates of trematode metacercariae were studied in fish from a polishing pond of a wastewater treatment factory and from Bang Yai Canal, Mueang District, Phuket Province, Thailand. The investigation was carried out from April 2001 to April 2002. Nile tilapia (Tilapia nilotica) were collected from the polishing pond, while mullet (Valamugil cunnesius) were collected from Bang Yai Canal. The metacercariae were examined from the fish’s dorsal fins, pectoral fins, ventral fins, digestive tracts, and gills. One hundred and twenty-eight Nile tilapia were collected and seven were found infected with metacercariae (5.5%). One hundred and thirtyone mullet were collected and 128 were infected with the parasites (97.7%). In the Nile tilapia, the metacercariae were found from the dorsal fins, pectoral fins, and gills at 3 (42.9%), 3 (42.9%), and 1 (14.3%) cysts, respectively. For the mullet, the metacercariae were found from the dorsal fins, pectoral fins, ventral fins, digestive tracts, and gills at 1,887 (42.4%), 339 (7.6%), 329 (7.4%), 869 (19.5%), and 1,031 (23.1%) cysts, respectively. One-way ANOVA tests (F test) were used to compare the infections of trematode metacercariae statistically. It was found that the infection rates of metacercariae at different months exhibited significant differences (p < 0.05), whereas the number of metacercariae found at different parts of the fish samples were not significantly different (p >