Effect of dietary phenylalanine level on growth performance, body composition, and biochemical parameters in plasma of juvenile hybrid tilapia, Oreochromis niloticus x Oreochromis aureus

An 8-week feeding trial with juvenile hybrid tilapia (Oreochromis niloticus x Oreochromis aureus) was conducted to assess the effects of dietary phenylalanine on growth, body composition, and biochemical parameters in plasma. Six diets were formulated with graded levels of l-phenylalanine (0.43, 0.74, 1.01, 1.30, 1.60, and 1.91% of the diet). Each diet was randomly assigned to triplicate groups with 20 fish per replicate (5.63 +/- 0.04 g). Weight gain, thermal growth coefficient (TGC), and protein retention efficiency (PRE) increased with the increasing levels of dietary phenylalanine, up to 1.30%, and declined slightly at higher levels. The ratio of whole-body protein and lipid was significantly higher in fish fed 1.30% phenylalanine compared with those fed 0.43% phenylalanine (p < .05), whereas whole-body moisture contents showed a decreasing trend. Plasma lysozyme and catalase activities and total protein were improved by the phenylalanine supplementation, while alanine aminotransferase and aspartate aminotransferase activities showed a converse trend. Based on broken-line regression analyses of TGC and PRE against different dietary phenylalanine levels, the value of optimal dietary phenylalanine requirement for juvenile hybrid tilapia might be estimated at 0.878%.