ABSTRACT
The use of microalgae in the field of fish feeding is still operated in a small scale. This study was conducted to evaluate the effects of using the microalga Spirulina platensis powder as a feed additive in fish diets. So, we use a total number of 120 apparently healthy Oreochromis niloticus, with average body weight of fish [50 +/- 5g] were obtained from Barseek fish farm at Behera Governorate. The present work was designed to investigate the different immunostimulant effects of Spirulina on some cultured freshwater fish including serum proteins, [Lymphocytes and monocytes] as well as phagocytic activity, index and the level of antibody titer, relative level of protection. For these investigations four experimental diets were carried out by addition of Spirulina platensis powder to balanced fish diet. 1[st] group: fed on 1[st] diet which is formed of fish diet with addition of 2.5% Spirulina platensis powder to it. 2[nd] group: fed on 2[nd] diet which is formed of fish diet with addition of 5% Spirulina platensis powder to it. 3[rd] group: fed on 3[rd] diet which is formed of fish diet with addition of 10% Spirulina platensis powder to it. 4[th] group: fed on 4[th] diet which is formed of fish diet without addition of Spirulina platensis powder to it [Control group]. The most important results of this study include: 1.There was a tendency for the WBCs values had the highest values during addition of Spirulina also there was increasing in lymphocyte and monocytes in groups fed on Spirulina than the control groups. 2. Fish groups supplemented with Spirulina showed increased of phagocytic activity and phagocytic index until the 4[th] weeks from feeding Spirulina. 3. In the present work, the significant increase in albumin, globulin and total protein and increase of albumin/globulin [A/G] ratio in the groups fed on Spirulina than control group 4. The antibody titers in all Spirulina supplemented groups were highor than the control feed on basal diet where ranged between 2 +/- 0.1, 3 +/- 0.1, 4 +/- 0.3 and 4 +/- 0.3 during 1[st], 2[nd], 3[rd] and 4[th] weeks respectively and at the end of the 4[th] week, the antibody titers ranked in groups where the 10% Spirulina supplemented group come in the first rank, followed by 5% Spirulina supplemented group, then 2.5% Spirulina supplemented group while the control group came in the last rank in values. 5. The potency of bacterin was examined by calculating the relative level of protection [RLP]. In this study, we examined the disease resistance in Spirulina - treated tilapia using the tilapia pathogen Aeromonas hydrophila