Dietary Hydrilla verticillata extract enhances growth and immune defense against Aeromonas hydrophila in Labeo rohita.

This study investigated the effects of dietary Hydrilla verticillata extract (HVE) on growth performance, physiological responses, and disease resistance in Labeo rohita fingerlings subjected to Aeromonas hydrophila challenge. Following acclimatization, the fish were divided into 15 tanks at random (30 fish per tank) and given five different diets that contained 0, 75, 150, 300, or 600 mg/kg HVE for 60 days. Growth was significantly (P < 0.05) boosted by dietary HVE, with 300 mg/kg showing the maximum weight gain and protein efficiency ratio, however, higher dose (600 mg/kg) reduced the growth performance. In HVE-fed groups, malondialdehyde levels dropped and antioxidant enzyme activity (SOD, CAT, and GPx) significantly increased, suggesting improved oxidative state. Elevated ALP, decreased AST and ALT activity, and decreased serum glucose and cortisol levels all indicated enhanced hepatic function and less stress. At 300 mg/kg, nonspecific immunological responses, such as lysozyme activity and total immunoglobulins, were markedly increased. Cumulative mortality decreased dramatically in HVE-supplemented groups after the A. hydrophila challenge, with fish fed 300 mg/kg exhibiting the lowest cumulative mortality. The optimal dietary HVE level was calculated as 252.46 mg/kg based on weight gain%. These results show that dietary HVE, especially 300 mg/kg, significantly enhances Labeo rohita growth, antioxidant defence, immunological function, and resistance to A. hydrophila.