Antiprotozoal activity of medicinal plants against Ichthyophthirius multifiliis in goldfish (Carassius auratus).

Ichthyophthiriasis is a widespread disease in aquaculture and causes mass mortalities of fish. The development of new antiprotozoal agents for the treatment of Ichthyophthirius multifiliis infections is of increasing interest. The aim of the present study was to investigate the efficacy of 30 medicinal plants against I. multifiliis. The results showed that the methanol extracts of Magnolia officinalis and Sophora alopecuroides displayed the highest antiprotozoal activity against theronts, with 4-h LC(50) values estimated to be 2.45 and 3.43 mg L(-1), respectively. Concentrations of 2.5, 5.0, 10.0, and 20.0 mg L(-1) of M. officinalis extracts resulted in tomont mortality of 9.7, 43.7, 91.3, and 100% at 20 h, respectively. From 40 to 320 mg L(-1) of S. alopecuroides extracts, tomont mortality increased from 29.7 to 100%. Antiprotozoal efficacy against settled tomonts (2 and 10 h) was also applied; the results indicated that encysted I. multifiliis tomonts were less susceptible to these plant extract treatments. In vivo experiments demonstrated that high concentrations of M. officinalis and S. alopecuroides extracts could kill tomonts, and M. officinalis significantly reduced its reproduction (P < 0.05). These results suggested that the methanol extracts of M. officinalis and S. alopecuroides have the potential to be used as an eco-friendly approach for the control of I. multifiliis.