A 12-week growth trial was conducted to determine the effects of dietary protein on the growth of the yellow tail cichlid, Pseudotropheus acei, and on water quality in closed recirculating systems. Six test diets were formulated to contain protein levels ranging 25-50% by substituting corn oil and alpha-starch for fishmeal. Diets were assigned to triplicate groups of 10 fish in a completely randomized design. The feed conversion ratios of fish fed the 35% and 50% crude protein diets were significantly (p<0.05) lower than that of fish fed the 30% protein diet. The protein efficiency ratio declined as the dietary protein level increased. Dietary protein levels significantly influenced total ammonia-nitrogen excretion (TAN); fish fed 50% protein excreted higher concentrations of ammonia-nitrogen than fish fed 25-35% dietary protein (p<0.05). Results suggest that inclusion of more than 35% protein in diets containing 10% crude lipid does not benefit juvenile yellow tail growth performance. Further, as TAN excretion and feed costs increased at protein levels beyond 35%, we recommend a diet containing 35% protein and 10% lipid for promoting good growth of juvenile yellow tail cichlids under the conditions used in the present trial.