الفهرس 
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Abstract
This study was conducted to investigate the role of two microalgae and their combinations in growth
performance, hematological, biochemical, immunological and histopathological changes in Nile tilapia. A total
number of 180 healthy Nile tilapia (Oreochromis niloticus) with an average body weight (31.89 ± 0. 29 g) were
distributed into 4 groups that stocked in 12 glass aquaria (15 fish/aquarium/replicate). Fish groups were fed
experimental diets as following; the first group (T0) fed basal diet only as control, the second & third groups fed
basal diet supplemented with 0.5% Spirulina platensis (TS) and 0.5% Chlorella vulgaris (TC) powders;
respectively. The fourth group (TSC) fed basal diet with combinations of the two algae powders with the same
concentration (0.5% S. platensis and 0.5% C. vulgaris). The treatment continued for 60 days as feeding period
followed by 10 days for challenged with pathogenic strains of Aeromonas hydrophila and Pseudomonas
fluorescence.
After feeding period, the growth parameters revealed significantly improved in TSC group, when compared
to other groups. The hematological analysis showed non-significance changes in blood parameters among all
experimental groups, except the leukocytic count was significantly up regulated in TC & TSC groups when
compared to control. Additionally, hepatorenal and stress biomarkers (ALT, AST, Urea & Cortisol) exhibited
non-significant changes among all fish groups. The immune status displayed enhancement that represented by
significant elevation in Respiratory burst activity (RBA) among algal supplemented groups when compared to
control group with non-significant change in IgM & NO values between all groups.
During histopathological examination, normal tissues architecture and cellular details of intestine, liver,
spleen & kidneys form all experimental fish groups were noticed without any obvious alteration lesions after
feeding period. Moreover, significant improvement in intestinal morphometry (villi length & width, absorption
area, tunica musularis thickness and number of goblet cells) as well as splenic morphometry (number and size
of melanomacrophage centers, MMCs) in algal supplemented groups compared with control group.
Following challenge infection, the cumulative survivability among experimental groups after 10 days of
observations revealed significant increase in TC group, followed by TSC & TS groups when compared with
control group with survival rate of 90%, 80%, &70 and 0%; respectively.
The present study findings recommended the dietary inclusion of S. platensis and C. vulgaris with optimum
doses in aquafeed as they strongly improved growth, and immune responses of Nile tilapia and their disease
resistance against threatened bacterial pathogens.