Freshwater macrophytes, including duckweeds are a rich source of amino acids and fatty acids and have been considered as potential ingredients in fish feeds. The aim of the present study was to evaluate the effect of greater duckweed Spirodela plolyrhiza in feeds for rohu Labeo rohita. Four test diets (30% protein) containing 5 (diet 1, D1), 10 (diet 2, D2), 15 (diet 3, D3) and 20% (diet 4, D4) duckweed and a control diet without duckweed (diet 5, D5) were prepared using a Twin-Screw Extruder. There was no significant difference in protein, lipids and ash contents among the diets, but free amino acids and fatty acids levels were lower in the control diet compared to the test diets. Rohu (1.73 ± 0.22 g) were fed ad libitum for 60 days. The final average weight and specific growth rate were significantly higher (P < 0.05) and feed conversion ratio was lower in rohu fed diets D1, D2 and D3 compared to the fish fed the other diets. Protein and lipid contents were significantly lower (P < 0.05) in rohu fed the control diet compared to fish fed the test diets. Essential, non-essential and free amino acids levels were also significantly lower (P < 0.05) in the control group compared to the other groups. Omega-3 polyunsaturated fatty acid contents were significantly higher (P < 0.05) in rohu fed all test diets compared to fish fed the control diet. Highest and lowest lipase activities were found in rohu fed diets D1 and D4, respectively. Expression levels of delta-6-desaturase (fads2d6), fatty acid synthase (fas) and elongation of very long chain fatty acid 5 (elovl5) were highest in rohu fed diet D1.