Lotus Elixir: A melody of gene expression variation in Oncorhynchus mykiss tissues

The present study evaluated the survival and immune response of Rainbow trout ( Oncorhynchus mykiss) fingerlings fed with Nelumbo nucifera leaf extract (NNLE) for 90-day time period. Two hundred and fifty fingerlings were randomly distributed into five treatment groups in triplicates. Each group was fed isonitrogenous and isoenergetic regimes containing 0% NNLE (control), 0.25% NNLE (T1), 0.75% NNLE (T2), 1.25% NNLE (T3), and 1.75% NNLE (T4) to satiation. NNLE was found to significantly (P < 0.05) reduce malate dehydrogenase and aspartate amino-transferase activity in the liver tissue. Alanine amino-transferase activity in the muscle tissue of NNLE fed groups was significantly higher than in the control. The liver and gill superoxide dismutase activity were significantly reduced in the NNLE fed groups compared to the control. Also, the catalase activity in the liver and gill got significantly lowered in the T4 group. NNLE fed groups showed elevated RBC, TLC, respiratory burst activity, lysozyme activity and phagocytic activity compared to control group. Also, mRNA expression of defensin and hepcidin genes showed significant upregulation in NNLE fed groups thereby highlighting its role in modulation of innate immune response. During pre-challenge phase, pro inflammatory cytokines were significantly (p<0.05) down-regulated compared to control. Whereas, post-challenge period, T4 (1.75% NNLE) caused substantial (p<0.05) up-regulation of IL-1 and TNF-α1 expression. Regulatory cytokines were slightly up-regulated during pre-challenge and down-regulated post-challenge periods. Treatment groups T3 and T4 showed significantly (p<0.05) higher survival rate after challenged with pathogenic bacteria Aeromonas hydrophila . The study highlights that supplementation of Indian lotus leaf extract at the rate of 1.75% in diet enhances the disease resistance in rainbow trout.