Growth and digestive enzyme activities of rohu labeo rohita fed diets containing macrophytes and almond oil-cake

•Rohu were fed with almond oil-cake/ duckweed/ water fern and fishmeal blend diets.•Highest growth was found in duckweed-based diet fed rohu.•Duckweed is a rich source of amino acids for rohu.•Feed composition influenced amylase, protease and lipase activities.•Duckweed helped to replace 300 g/kg dietary fishmeal without affecting growth. The impact of plant-based diets on the digestive physiology of rohu Labeo rohita fingerlings (10.66 ± 0.53 g) was evaluated. A diet with all protein supplied by fishmeal was included as a control (F). Four test diets containing 300 g/kg protein were formulated using the following plant ingredients and fishmeal in a 1:1 blend: almond oil-cake Terminalia catappa (FTC), duckweed Lemna minor (FLM), water fern Salvania molesta (FSM) and combination of these three ingredients (FTCLMSM). The final body weight and specific growth rate were significantly higher in rohu fed diet FLM compared to the other treatments. Significantly lower feed conversion ratio in rohu fed diet FLM showed that diet was utilized efficiently in this feeding regime compared to the other diets. The composition of diets also influenced the digestive enzyme activities of the fish. Thus, amylase, trypsin and chymotrypsin activities were significantly higher in rohu fed diet FLM compared to the rohu fed the other diets. Protease activity was significantly higher in rohu fed diets FTC and F and lipase activity was significantly higher in rohu fed diet FTC compared to the rohu fed the other diets. The inclusion of raw duckweed in feed replaced 300 g/kg of dietary fishmeal without affecting growth.