Dietary Protein Demand of the Juvenile Blue Discus Symphysodon Haraldi

A 63-d experiment was conducted to investigate the dietary protein demand of juvenile Blue Discus Symphysodon haraldi. Five isoenergetic and isolipidic diets were formulated to contain graded levels of crude protein (CP): 50% (CP50), 55% (CP55), 60% (CP60), 65% (CP65), and 70% (CP70). The results showed that survival rate was not affected by dietary protein level. Weight gain (WG) and specific growth rate (SGR) first increased and then decreased as dietary protein level increased, and the highest WG and SGR was observed in the CP60 group. In contrast, feed intake (FI) and feed conversion ratio (FCR) first decreased and then increased, and the lowest FI and FCR were both observed in the CP60 group. Protein efficiency ratio (PER) first increased and then decreased, and the highest PER was observed in the CP60 group. Both the hepatosomatic index and viscerosomatic index tended to decrease as dietary protein level increased. Crude protein content first increased and then decreased, while crude lipid content tended to decrease as dietary protein level increased. Quadratic regression analysis on the basis of WG, SGR, FI, FCR, and PER indicated that the optimum dietary protein level for juvenile Blue Discus was estimated to be 60.1-61.0% of dry matter.