Parasites of grouper (Epinephelus coioides) cultured in Thailand

Orange-spotted grouper (Epinephelus coioides) cultured in Thailand were examined for their parasites. There were five parasitic groups found in this investigation, viz., protozoans (four genera), monogeneans (five genera), digeneaus (three genera), nematodes (two genera) and crustaceans (two genera). Two ciliated protozoans, Trichodina sp., Cryptocaryon irritans and a single species of Amyloodinium sp. (flagellated protozoan) were observed externally on the gills and skin, while Sphaerospora sp. (myxozoan) was found to parasitize in the kidney tubules of fish samples. Eight species of monogeneans were found, viz., Diplectanum grouperi, Pseudorhabdosynochus coioidesis, P. lantauensis, P. epinepheli, Haliotrema sp., two undescribed of Pseudorhabodosynochus, Megalocotyloides sp. from the gill and one species of monogenean, Benedenia epinepheli, from the skin. Digeneans, Aphanurus stossichi and Prosorhynchus pacifica, were found in the alimentary tract and a species of didymozoid, Gonapodasmius epinepheri, was present as yellow cysts attached to the gill filament. Two species of rare Philometru sp. and anisakid larva were observed on the body wall near the rectum and in intestine, respectively. Two groups of crustaceans were found as external parasites, Caligus (copepod) and Rhaxanella (isopod). Monogeneans seemed to be major parasites of orange-spotted grouper in this study, which was indicated by the great numbers and occurrence of Diplectanum eplnepheli. There was no significantly different in parasite of abundance during their own groups along the sampling period. Overall water quality parameters studied were stable, except transparency that fluctuated depending on the rainfall and tide. The occurrence of monogeneans showed correlation to water transparency. All fish samples showed no abnormal sign or symptom caused by parasitic infection.