A feeding trial of 60 days was conducted to delineate the effect of dietary synbiotic on maximum growth, body composition, digestive enzyme activity and subsequently gut microbiota in Cirrhinus mrigala fingerlings. One hundred and eighty acclimatized fingerlings of mrigal with initial body weight ranging from 2.87 ± 0.01 g to 3.26 ± 0.05 g were randomly distributed in three replicates of each of four experimental groups including control (without probiotic and prebiotic), T 1 (high probiotic + low prebiotic), T 2 (low probiotic + high prebiotic) and T 3 (high probiotic + high prebiotic), using completely randomized design (CRD). Results showed that growth performance parameters, such as specific growth rate (SGR), per cent weight gain, feed conversion ratio (FCR) and protein efficiency ratio (PER), were reported to be higher in the T 2 group followed by the T 3 group. Maximum gut microbiota activity was found in the T 3 group which was significantly different from other treatment groups. Similarly, body composition and digestive enzyme activity varied significantly (p < .05) among the treatment groups. The study showed the possibility of improved nutrient utilization in terms of growth performance and digestive enzyme activity in the group following dietary synbiotic supplementation. K E Y W O R D Sdigestive enzyme, gut microbiota, prebiotic, probiotic

A feeding trial was conducted for 90 days to assess the metabolic and digestive enzyme activity in response to alternate or mixed feeding of different protein levels in the diet of Pangasianodon hypophthalmus fingerlings. One hundred and forty four fingerlings with an average weight of 5.0-5.5 g were distributed into four experimental groups each with triplicate. Four iso-caloric diets with varying level of crude protein viz., 35%, 30%, 25% and 20% were made and designated as diet 35P, 30P, 25P and 20P respectively. Four treatments were maintained based on four different feeding schedules such as continuous feeding of diet 35P (35P/35P), alternate feeding of 1 day diet 35P next day diet 30P (35P/30P), alternate feeding of 1 day diet 35P next day diet 25P (35P/ 25P) and alternate feeding of 1 day diet 35P next day diet 20P (35P/20P). As a result, specific growth rate (SGR) and weight gain percentage were relatively higher in treatment (35P/25P) followed by (35P/35P) and (35P/30P). The metabolic enzymes such as lactate dehydrogenase (LDH), malate dehydrogenase (MDH), glucose-6-phosphate dehydrogenase (G6PDH), Glucose-6-phosphatase (G6Pase), alkaline phosphatase (ALP), acid phosphatase (ACP), alanine aminotransferase (ALT), aspartate aminotransferase (AST) were expressed better in (35P/35P) group followed by (35P/25P) and (35P/30P) groups. The digestive enzymes, protease and lipase activities were higher in (35P/35P) and (35P/ 25P) groups. The present study revealed that the better nutrient utilization and growth of 35P/25P group is because of their balanced digestive and metabolic enzyme activities through alternate level of higher and lower protein diet.