This experiment was conducted to evaluate the
use of ethanol-extracted from the medicinal
plant, Origanium vulgare as a growth and
immunity promoter for Nile tilapia, Oreochromis
niloticus (L.) fingerlings. Fish (average 12.27 g)
were randomly distributed into four treatments;
three replicates each at a rate of 20 f i sh per 100
L aquarium. Fish were fed one of the tested
diets containing similar crude protein (30 %)
and gross energy (4.40 KCal/g), in addition to
0.0, 0.5, 1.0, or 1.5 % Origanium vulgare
extract. Diets were given twice daily at a rate of
3 % of live body weight, for six days a week
during 10 weeks. After the feeding t r i a l , fish of
each treatment were challenged by pathogenic
Pseudomonas aeruginosa and Pseudomonas
flourscence, which was given by intraperitoneal
(l/P) injection and they were kept under
observation for 10 days to follow up any
abnormal clinical signs and the daily mortality
rate. The growth-promoting influence of
Origanium vulgare extract was observed on
f i s h . The maximum growth was observed at 0.5
% Origanium vulgare extract as compared to
the control. No significant differences in fish
survival were reported among the experienced
treatments at (P>0.05), f a l l i ng within the range
of 93.3 - 100%. The control fish consumed less
diet and gave a higher FCR, while fish fed diet
containing 0.5 % Origanium vulgare extract
demonstrated the highest protein efficiency
ratio (PER), apparent protein utilization (APU),
and energy utilization (EU). The
supplementation of Origanium vulgare extract
had no significant (P>0.05) effect on the fish
body composition (dry matter, crude protein, fat,
and ash), meanwhile, total protein, albumin, and
globulin increased significantly (P