Use of asiatic pennywort Centella asiatica aqueous extract as a bath treatment to control columnaris in Nile tilapia.

To develop antibiotic-free and chemical-free aquaculture, it is necessary to have natural substances to control diseases of aquatic animals. The aim of this study was to find an herb having therapeutic effect against columnaris, a fish disease caused by the bacterium Flavobacterium columnare. Of all tested herbs (including kalmegh Andrographis paniculata, candle bush Cassia alata, Asiatic pennywort Centella asiatica, mangosteen Garcinia mangostana, pomegranate Punica granatum, and guava Psidium guajava), the aqueous extract of Asiatic pennywort exhibited the strongest antimicrobial activity against F. columnare; the minimal inhibitory concentration was 31.25 lg/mL. It was also found to have a bactericidal effect on F. columnare. When experimental bath exposures of Nile tilapia Oreochromis niloticus to F. columnare were performed, the median lethal dose was determined to be 2.37 x 10(5) colony forming units/mL. For in vivo trials, six different concentrations (0, 20, 40, 60, 80, and 100 mg/L) of Asiatic pennywort aqueous extract were used as bath treatments to control experimentally induced columnaris in Nile tilapia. The decrease in fish mortality was dose dependent, and at a concentration of 100 mg/L no mortality or adverse effects were noted in the infected fish. This study suggests that Asiatic pennywort aqueous extract has the potential to control disease caused by F. columnare.