The study evaluated the effect of dietary doses of Euglena viridis on the immune response
and disease resistance of Labeo rohita fingerlings against infection with the bacterial
pathogen Aeromonas hydrophila. L. rohita fingerlings were fed with diet containing
0 (Control), 0.1 g, 0.5 g, 1.0 g Euglena powder kg(-1) dry diet for 90 days. Biochemical
(serum total protein, albumin, globulin, albumin:globulin ratio), haematological (WBC,
RBC, haemoglobin content) and immunological (superoxide anion production, lysozyme,
serum bactericidal activity) parameters of fish were examined after 30, 60 and 90
days of feeding. Fish were challenged with A. hydrophila 90 days post-feeding and
mortalities were recorded over 10 days post-infection. The results demonstrate that
fish fed with Euglena showed increased levels of superoxide anion production, lysozyme,
serum bactericidal activity, serum protein and albumin (P < 0.05) compared with the
control group. Following challenge with A. hydrophila less survivability was observed
in the control group (56.65%) than the group fed the experimental diets. The group
fed 0.5 g Euglena kg(-1) dry diet showed the highest percentage survival (75%). These
results indicate that Euglena stimulates the immunity and makes L. rohita more resistant
to A. hydrophila infection.