The present study was carried out to study the preferred prey in the larval and post-larval stages of Heterobranchus lonsifilis. Two hundred and forty larvae and fry of H. longifilis aged 2 to 23 days were stored in aquariums of 8 liters, fasted for 24 hours at the end of which they were fed to satiety with freshly collected zooplankton from fishponds. The day after feeding, the fish were euthanized and stored for stomach contents examination. The results showed that the zooplanktonic population density of the station ponds was 1356.73 individuals / L. This stand is composed of Cladocerans (455.85 individuals /l), nauplii (289.11 individuals / l), Rotifers (255.47 individuals / l), Copepodites (182.21 individuals / l) and Copepods adults (174.07 individuals /l). Furthermore, examination of stomach contents showed that adult Copepods were the most frequent and abundant prey category in stomach contents in terms of frequency of occurrence (66.7%) and numerical percentage (48.25%). In addition, these preys (adult copepods) constituted the preferred zooplankton prey in larvae and post-larvae of H. longifilis with an electivity index (E) equal to +0.5. Apart from the first size classes in which no prey has been observed in the stomach contents, the food preferences of H. longifilis larvae and fry do not vary with the size of the individuals. This study showed that adult copepods were the preferred zooplankton prey of H. longifilis larvae and fry.