Harnessing the immunomodulatory potential of ashwagandha (Withania somnifera) against epizootic ulcerative syndrome: a sustainable approach for hill aquaculture.

The present study evaluated the immunomodulatory and disease resistance-enhancing effects of dietary supplementation of Withania somnifera root powder in Labeo rohita (22.10 ± 3.30 g, 12.35 ± 1.15 cm), a commercially important freshwater fish species, against Aphanomyces invadans infection under the agro-climatic conditions of Tripura, Northeast India. Four isonitrogenous and isocaloric experimental diets were formulated with varying levels of W. somnifera root powder: control (0%), D1 (0.1%), D2 (0.2%), and D3 (0.3%). After a 21-d feeding period, the fish were challenged with A. invadans zoospores (1 × 104 spores ml-1; 0.1 ml fish-1) and observed for mortality and blood parameter assessment according to standard protocols. The survival rate was markedly higher at 83.33% in the 0.2% W. somnifera group compared to 31.11% in the control group 14 d post-infection. Dietary W. somnifera supplementation improved serum protein, enzymatic, and hematological parameters. Immunological parameters, including nitroblue tetrazolium activity, serum lysozyme activity, and bactericidal activity, were also significantly higher in W. somnifera-fed fish. The findings suggest that W. somnifera root powder at 0.1-0.3% inclusion levels, with 0.2% being the optimal dose, can enhance disease resistance against A. invadans in L. rohita by modulating innate immune mechanisms. Given the growing concerns over antimicrobial resistance and the need for sustainable aquaculture practices, the use of natural immunostimulants such as W. somnifera offers a promising alternative for disease management, particularly in regions prone to epizootic ulcerative syndrome outbreaks.