Effect of galangal oil against Ichthyophthirius multifiliis theronts in freshwater fish.

Objective—To investigate the effects of galangal oil against Ichthyophthirius multifiliis infective stage (theront stage) isolated from infected freshwater fish. Materials and Methods—The essential oils were obtained from fresh rhizomes of Alpinia galanga by stream distillation. The oil was analyzed by gas chromatography-mass spectrometry. The theronts were isolated and divided into 6 groups of 600 theronts per group. Group 1 was a control group; group 2 was exposed to formalin at 50 ppm; group 3 was exposed to propylene glycol, groups 4-6 were exposed with 10, 30 and 60 ppm of galangal oil, respectively. Mean mortality of theronts was determined by light microscope at 1, 2, 4 and 6 hrs after treatment. Results—The GC-MS result indicated that the main compound of galangal oil is eucalyptol. The mean mortality was higher in groups 4-6 (exposed with 10, 30 and 60 ppm of galangal oil, respectively) than in groups 1-3 (control group, exposed to formalin and exposed to propylene glycol, respectively) at the first hour of the experiment (P<0.05). In addition, the mean mortality was higher in groups 5-6 (exposed with 30 and 60 ppm of galangal oil) than in group 4 (exposed with 10 ppm of galangal oil) at the first hour of the experiment (P <0.05), whereas the mean mortality in group 5 (exposed with 30 ppm of galangal oil) was not significantly different from that in group 6 (exposed with 60 ppm of galangal oil) at the forth hour of the experiment. Conclusion—Galangal oil has potential against I. multifiliis theronts. The lowest effective dose was 30 ppm. KKU Vet J. 2012;22(1):1-9. http://vmj.kku.ac.th/