The digestibility of four isonitrogenous practical diets (40% crude protein) containing different levels (5%, 15%, 25% and 35%) of gelatinized breadflour as carbohydrate source were determined for P. monodon (average weight 30–40 g). The digestibility coefficients for protein ranged from 92.8 to 94.3%. Crude fat digestibility ranged from 90.0 to 92.8% and dry matter digestibility from 75.7 to 86.9%. Carcass crude protein was similar in all treatments but carcass crude fat decreased significantly (P<0.05) with increasing dietary carbohydrate. The same diets were fed to a group of smaller P. monodon (average initial weight=0.139±0.011 g) for 8 weeks. Weight gain, specific growth rate (SGR), feed conversion ratio (FCR) and survival rate did not differ significantly (P>0.05) among treatments. However, weight gain and SGR were lowest and FCR was poorest with 35% carbohydrate.