The enhancement of phagocytosis observed in the present study
may be due to the influence of herbal extract. The O2
− is the first product
released during the respiratory burst, O2
− concentration has been accepted
as an accurate parameter to quantify the intensity of a respiratory
burst. The total number of NBT-positive
cells in blood kept rising in rainbow trout after treatment with
immunostimulant (Adams and Hamilton, 1984). These cells might be
the neutrophils that still retain the capacity for production of oxidativeradicals. In this study, the challenged fish fed with any supplementation
diet increased the serum bactericidal activity. Such increased bactericidal
properties could have resulted in reduced percentage of mortality
during 30 days on being fed with 5% and 10% diets. In addition, the
anti-protease activity also significantly was enhanced in 5% and 10%
diet fed groups from week 3 while it manifested in all enriched diet
on week 4. The superoxide anion production also was significantly enhanced
in all diet groups on weeks 3 and 4 against pathogen.