The use of blue-green alga Spirulina platensis biomass in improving the production and strengthening the immune system of Grass carp (Ctenopharyngodon idella) in the face of Aeromonas hydrophila bacteria.

Spirulina is used as a growth and immunity promoter for aquatic due to its bioactive compounds. In the present study examined the effect of blue-green alga Spirulina platensis biomass on growth performance, Secretions of digestive enzymes, blood physiological indices and resistance of grass carp (Ctenopharyngodon idella) infected with Aeromonas hydrophila. Fish (7.86 ± 0.47 g) were randomly distributed in 12 tanks (20 fish per 50 L). Also, together with the consumption of basic food (Protein 32.29% and energy 3984.80 kcal/kg), different levels of spirulina algae were added with a concentration of 4×104, 5×104 and 6×104 cells/ml (S1, S2 and S3, respectively) and basic food without algae (C), daily to rearing tanks for 60 days. The growth of fish in the treatments containing Spirulina was significantly higher and the feed conversion ratio was lower compared to the control treatment. Highest protease and lipase activities were observed in S2 and S3 treatments, respectively. The highest blood serum immune response (lysozyme, complement, total immunoglobulin) were observed in S2 and S3 treatments. The lowest and highest concentrations of superoxide dismutase (SOD) and malondialdehyde (MDA) were obtained in the C treatment. Bactericidal activity of fish serum was significantly higher in S2 and S3 treatments. The highest white blood cells and red blood cells, hemoglobin and hematocrit were at S3 treatment; meanwhile, the lowest value was obtained in the control. In general, physiological parameters such as growth efficiency, digestive secretions, immunity and bactericidal activity of blood serum were improved in grass carp fed with live spirulina algae with a density of 5×104 and 6×104 cells/ml (S2 and S3 respectively).