Effects of Dietary Blend of Algae Extract Supplementation on Growth, Biochemical, Haemato-Immunological Response, and Immune Gene Expression in Labeo rohita with Aeromonas hydrophila Post-Challenges

In this study, the effects of a mixed algal blend (Chlorella vulgaris, Euglena viridis, and Spirulina platensis) at different levels were evaluated on growth, hematological immune responses, and expression of immune genes in Labeo rohita against post-challenges of Aeromonas hydrophila. Fish samples were fed a diet containing different levels of mixed blend algal (0, 0.01, 0.02, 0.04 and 0.08% of basal diet). At the end of the feeding period, the fish were challenged with A. hydrophila and fish mortality was recorded over a 14-days period. To evaluate the serum biochemical (albumin, globulin), hematological parameters (Hb, RBC and WBC) and immune parameters (neutrophil activity, lysozyme activity, myeloperoxidase activity, antiprotease activity, ceruloplasmin activity, and bactericidal activity), as well as the expression of immune genes (NKEF-B, Lysozyme C and G, TNF α, TLR22, β2M, and β-actin), fish were sampled on Day 7, 14, 21 and 28. Fish were challenged with virulent A. hydrophila 30 days post-feeding and mortalities were recorded over 30 days post-infection. Results demonstrate that fish fed with a mixed algal blend showed that total body weight gain, specific growth rate, total serum protein, globulin, total hemoglobin content, white blood cells, neutrophil, lysozyme, bactericidal, myeloperoxidase, and antiprotease activity in dietary algae blended application was higher than in the control (p < 0.05). According to the results, relative expression of target genes showed significant increases of 0.02 to 0.04% in the treatment group compared to the control group (p < 0.05). At the end of the 30-day exposure to A. hydrophila, the fish that received the mixed algal blend had a significantly higher rate of survival than the control group, with the highest survival rate recorded in the 0.02% mixed algal blend (p < 0.05). According to the effective results of the mixed algal blend on stimulating the immune system and increasing fish resistance to A. hydrophila, it is recommended to use 0.02 to 0.04% of this mixed algal blend in rohu, L. rohita diets.