This study evaluated the effects of Hybanthus enneaspermus aqueous extract (HEE) as a feed supplement on growth, immune responses, haematological, and biochemical parameters of Labeo rohita and its susceptibility to Aeromonas hydrophila infection. Diets containing five variable concentrations of HEE (g kg−1) (0 [basal diet], 1.0 [H1], 2.0 [H2], 3.0 [H3], and 4.0 [H4]) were fed to fish (average weight: 17.2 ± 0.21 g) for 6 weeks. Growth parameters, immune parameters, and haemato-biochemical parameters were examined 6 weeks post-feeding. The results showed that growth parameters, such as final weight (39.47 ± 3.1 g) and specific growth rate (1.92 ± 0.2), were significantly higher in the H3 group than in the control. Immunological parameters such as serum lysozyme (24.73 ± 2.16 U mg−1), phagocytic activity (19.14± 0.26%), and respiratory burst activity (0.307 ± 0.005) were significantly higher in the H3 group, compared with the control. Among the haematological parameters examined, red blood cells, white blood cells, neutrophils, total serum protein, and albumin levels were significantly higher in the H3 group. However, HEE administration had no significant effect on haematocrit, haemoglobin, monocytes, or eosinophils levels. Blood biochemical parameters, including superoxide dismutase and alkaline phosphatase activities, were higher (P < 0.05) in the H3 group than in the control; however, the opposite result was found for aspartate transaminase, alanine transaminase, glucose, and cholesterol. Supplementation with 3 g kg−1 HEE increased the activities of intestinal digestive enzyme (amylase, protease, and lipase) in fish. Moreover, fish fed diets supplemented with 3 g kg−1 HEE exhibited the highest disease resistance against A. hydrophila infection. These results suggest that dietary administration of HEE (at 3 g kg−1) has several positive effects on growth, immune and haematological responses in L. rohita.