Effect of plant active compounds on immune response and disease resistance in Cirrhina mrigala infected with fungal fish pathogen, Aphanomyces invadans

The antibacterial activity of individual and mixed medicinal plant compounds, azadirachtin (Az), camphor (Ca) and curcumin (Cu), was tested at 100, 200, 300, 400, 500, 600 and 700 ppm (mg L-1) against fungal fish pathogen, Aphanomyces invadans, in vitro. At the lower concentrations between 100 and 300 ppm, the mixture of the tri-herbal (Az+Ca+Cu) compound yielded a higher (P > 0.05) zone of inhibition (ZI) of 7 mm than the positive control; the maximum ZI values (8-15 mm) were realized between 400 and 700 ppm (P < 0.05). At the lowest minimum inhibitory concentration (MIC) the tri-herbal compound (100 ppm) yielded 13 colony-forming units; hence, this dose can be effectively used at the lowest concentration of 100 mg L-1 to ward off the growth of A. invadans in vitro. In Cirrhina mrigala, intramuscular administration (100 mu L) of the selected doses of 100, 400 and 700 ppm (mg L-1) significantly enhanced (P < 0.05) the serum lysozyme activity (Ly), production of reactive oxygen species and reactive nitrogen species (RNS or NO) by peripheral blood leucocytes on the 10th, 20th and 30th day. A priori administration of the compound in the fish (100 ppm on 30th day) decreased the percentage mortality when challenged with the pathogen while in the untreated group the mortality increased (P < 0.05). This study indicates that intramuscular administration of the tri-herbal compound Az+Ca+Cu at a concentration of 100 ppm could augment the immune response in C. mrigala against A. invadans.