Dietary emodin affects the growth performance, immune responses, and disease resistance of Labeo rohita against Aeromonas hydrophila

Healthy Labeo rohita (mean bodyweight of 20.1 g) were divided into four groups before being fed for 60 days on diets supplemented with 0 (control), 20 (E1), 30 (E2), or 40 (E3) mg kg−1 emodin. Various growth and immune parameters were measured after 15, 30, 45, and 60 days of feeding. Fish fed E2 diet exhibited accelerated (p < 0.05) weight gain after 30–60 days of feeding. The most significant improvements (p < 0.05) in immune parameters, such as lysozyme activity, alternative complement pathway activity, respiratory bursts activity, phagocytic activity, superoxide dismutase activity, and myloperoxidase activity, were observed in the E2-fed group after 30 and 45 days of feeding. However, fish groups fed E2 or E3 diets exhibited significantly lower malondialdehyde, aspartate aminotransferase, and alanine aminotransferase activities than did the control group after 30 and 45 days of feeding. The IgM level was significantly elevated in treatment groups after 30 and 45 days of feeding. Further, fish fed E2 diet for 45 days had the highest (p < 0.005) post-challenge survival rate (83.3 %), followed by fish fed E2 diet for 30 days (75 %). Therefore, dietary feeding of emodin at 30 mg kg−1 to L. rohita for 30–45 days is optimal to enhance the immunity and disease resistance against A. hydrophila.