Addition of bromelain enzyme to a plant-based diet in Labeo rohita fingerlings: Effects on growth, body composition, enzyme activities, and intestinal morphology

This study investigated the impact of bromelain supplementation in plant based-diet on the growth, enzymatic activity, and intestinal morphology of Labeo rohita. A total of 300 fingerlings (initial weight, 12.27 ± 0.11 g) were acclimatized and randomly distributed into 15 aquaria (20 fish/aquarium), which were fed diets (30% CP) supplemented with bromelain at concentrations of 0, 10, 20, 30, and 40 g/kg (D₀, D₁, D₂, D_3, and D_4, respectively) in triplicate for 90 days at a 3% body weight ratio. Bromelain supplementation up to 20 g/kg significantly (p < 0.05) increased weight gain and the specific growth rate; however, higher supplementation levels reduced (p < 0.05) growth performance. Similarly, the fish fed up to 20 g/kg bromelain-supplemented diet presented a significantly (p < 0.05) lower FCR, and the opposite trend was observed at higher levels. Compared with those in the control group, significant (p < 0.05) increases in the activities of digestive enzymes, such as proteases and lipases, were observed in the fish fed diets supplemented with up to 20 g/kg bromelain, and the opposite trend was observed at higher supplementation levels. However, amylase activity was reduced (p < 0.05) in the fish fed up to 20 g/kg bromelain supplemented diets in comparison to control group. No significant changes (p > 0.05) in survival rate or body composition (moisture, crude fat, ash, or crude protein) were noted. The contents of minerals, particularly copper, zinc, calcium and magnesium, in the fillets decreased significantly (p < 0.05) in the fish fed with bromelain-supplemented diets, and the opposite trend was observed for phosphorus. Furthermore, bromelain supplementation up to 20 g/kg significantly (p < 0.05) improved serum alkaline phosphatase activity and intestinal morphology, increasing the goblet cell count, mucosal length, villus length, and width; however, higher levels had opposite effects. Moreover, polynomial regression analysis revealed 25.89 g/kg bromelain as the optimal concentration for enhancing the growth and health status of L. rohita, which highlights the potential of bromelain as an effective dietary supplement to increase fish performance in plant-based aquaculture systems. Future research should focus on large-scale applications, economic feasibility, and synergistic effects with other feed additives to reduce the reliance on fishmeal in aquafeed.