The effects of neuropeptide Y (NPY) administered intramuscularly or orally on postlarvae (PLs) of two penaeid species were investigated in this study. In experiment 1, food intake (FI) of Marsupenaeus japonicus PLs (0.96 g), injected with NPY at 0.6 mug per g BW, was investigated within 48 h posttreatment. In experiment 2, oral administration of NPY (at doses of 0, 0.125, 0.25, 0.5 mug g(-1) food) on feed intake and growth performance of Penaeus semisulcatus PLs (0.27 g) was examined for 6 weeks. In experiment 1, NPY injection significantly increased average daily FI of M japonicus PLs within the first 24 h compared to the control (P<0.05), but its stimulatory effect decreased on the second day (P>0.05). The increase in FI was 33% during the first 24 h and 17% during the next 24 h. In experiment 2, significant (P<0.05) differences were found among the groups in terms of weight gain and food utilization (P<0.05). Mean FI significantly increased (as much as 1.3-fold over the control) when NPY was orally administered at doses from 0.125 to 0.5 mug g(-1) feed. There was a positive relationship between FI and final weight (y=-0.972+2.098x, R-2=0.81) and between FCE and NPY doses in the diets (y=45.37+3.46x, R-2=0.91). The present findings indicated for the first time that NPY is a potent stimulator of food intake when administered either intramuscularly or orally to penaeid shrimps. (C) 2004 Elsevier Inc. All rights reserved.