Transformation of food has been studied in the euryhaline fish Ambassis gymnocephalus (Lacepede) by using energy transfer criteria. Duration of the experiments varied from 15-21 days. Flesh of the prawn Metapenaeus dobsoni was used as food. The absorption efficiencies are more than 96 % and conversion efficiencies vary between 20.57 and 27.73% in different weight groups of fish. The conversion efficiency of A. gymnocephalus was found to be lower than that of young ones of similar size of fishes, that grow to larger size.