In order to determine theadequate Crude Protein (CP)/ Calculated Digestible Energy (CDE) ratio in a diet for bocachico fries (Prochilodus magdalenae) an experi- ment, lasting 60 days, was designed within 24 aquari- ums, located within the Fish Nutrition Laboratory of Fac- ulty ofVeterinary Medicine and Zootecnia of the National University of Colombia, Bogota. Due to the animais sus- ceptibility to manipulation, measurements were only made at day 0 and than on days 30 and 60. Food was offered three times a day, at 8:00 am, 12:00 m and 4:00 pm, taking into account 15% of the fries biomass de- posited in each aquarium. Daily 15% of the water in each container was changed and 80% water change was made weekly, including filter cleaning. Six experimental diets were elaborated and evaluated, including two protein levels, 34% and 36%, and three levels of CDE, 3000, 3100 and 3200 kcal/kg. The variables evaluated were weight gain expressed as percentage, specific growth rate, standard length and feed efficiency. The highest percent weight gain and rate of specific growth were obtained with the diet that contained 36% of crude protein and 31 00 kcal/kg of CDE, corresponding to 116.12 of mg CP/kcal. The other variables did not show signifi- cant differences (P<0.05).