Effects of hot-water extract of Toona sinensis on immune response and resistance to Aeromonas hydrophila in Oreochromis mossambicus.

Respiratory burst, lysozyme and phagocytic activities, and immunoglobulin levels in response to the pathogen Aeromonas hydrophila were examined in tilapia (Oreochromis mossanbicus, 10.65 +/- 2.5 g) injected individually with hot-water extract of Toona sinensis at 4 or 8 microg g(-1). Tilapia receiving the hot-water extract of T. sinensis at either dose had significantly increased respiratory burst, phagocytic activity and lysozyme activity towards A. hydrophila by 1 and 2 days post injection. No significant differences in total immunoglobulin levels were observed among the tilapia that received the two different doses of hot-water extract of T. sinensis at 4 and 8 microg g(-1). In another experiment, a Tilapia that had been injected with hot-water extract of T. sinensis was challenged with A. hydrophila at 5 x 10(7) colony-forming units (cfu) fish(-1). The survival of tilapia that received the hot-water extract of T. sinensis at 8 microg g(-1) was significantly higher than fish that received phosphate buffered saline and the control fish after 2 days, and at the termination of the experiment (7 days after the challenge). It was concluded that the hot-water extract of T. sinensis at 8 microg g(-1) or less had increased the immune response and resistance to A. hydrophila infection in tilapia.