Optimum Dietary Protein Level and Protein‐to‐energy Ratio for Growth of Juvenile Parrot Fish, Oplegnathus fasciatus

An 8‐wk feeding trial was conducted to estimate the optimum dietary protein level and protein‐to‐energy (P/E) ratio in juvenile parrot fish, Oplegnathus fasciatus . Eight experimental diets were formulated with two energy levels and four protein levels for each energy level. Diets containing crude protein ( CP ) at 35, 40, 45, and 50% had either 12.5 or 14.6  kJ /g of energy. Fish averaging 7.1 ± 0.06 g (mean ±  SD ) were fed one of the experimental diets for 8 wk. At the end of the feeding trial, weight gain ( WG ) of fish fed 45 and 50% CP in the 12.5  kJ /g diet was significantly higher than fish fed the 35% CP diet ( P  < 0.05). WG of the fish fed 45 and 50% CP in the 14.6  kJ /g diet was significantly higher than fish fed the 35 and 40% CP diets ( P  < 0.05). Fish fed the 14.6  kJ /g diet had a higher WG compared with fish fed the 12.5  kJ /g diet at all CP levels. Feed efficiency ( FE ) and specific growth rate ( SGR ) showed a similar trend to the WG . WG , FE , and SGR improved with increasing dietary protein levels up to 45% and remained constant at 50% CP for both energy levels. However, protein efficiency ratio was negatively related to dietary protein levels. The results suggested that the optimum level of protein and the optimum P/E ratio for juvenile parrot fish should be 45% and 31.1 mg protein/ kJ , respectively, in a diet containing 14.6  kJ /g energy.