Discus (Symphysodon spp.), a valuable ornamental species (mean initial weig
ht 4.40-4.65 g) were fed five isoenergetic (gross energy: 200-209 kJ g(-1))
, semipurified diets (casein, gelatine and Danish fish meal as protein sour
ces) twice a day to satiation for 12 weeks. Five levels of protein were eva
luated (350, 400, 450, 500 and 550 g kg(-1) diet) and each fed to four repl
icates. Growth rate increased significantly with protein level up to 500 g
kg(-1) diet and then decreased. Feed conversion rates (FCRs) ranged from 2.
2 to 3.8, varying inversely with observed growth rate. A similar trend was
also observed in the efficiency of protein utilization (PER). Analysis of d
ose (protein level)-response (growth rate) with second order polynomial reg
ression suggested a requirement of 449-501 g kg(-1).