Effects of dietary modified palm kernel meal on growth, feed utilization, radical scavenging activity, carcass composition and muscle quality in sex reversed Nile tilapia (Oreochromis niloticus)

• Water soaking of palm kernel meal effectively modifies it beneficially for the diet.
• Soaking of PKM gave the fish superior growth performance and feed utilization.
• Digestive capacity of the fish improved with soaked PKM.
• Improved carcass and muscle were observed in fish fed soaked PKM.

Effects of dietary modified palm kernel meal (PKM) were investigated on growth performance, feed utilization, digestive enzyme specific activities, radical scavenging activity, carcass and muscle compositions, and muscle quality in sex reversed Nile tilapia (Oreochromis niloticus). The experiment was conducted in a completely randomized design with triplicate observations (4 treatments × 3 replicates × 8 fish per aquarium) during ten weeks of duration. The Nile tilapia (20.61 ± 0.15 g initial body weight and 10.45 ± 0.03 cm initial length) were fed with four isonitrogenous, isolipidic and isoenergetic diets containing 20% PKM, the treatments differing only in the nature of the PKM. It was either unprocessed (UPKM), water-soaked (SPKM), microwave-irradiated (MPKM), or water-soaked and microwave-irradiated (SMPKM). The fish fed with SPKM and SMPKM diets were superior in specific growth rate (P < 0.05) and feed conversion ratio (P > 0.05) when compared with the UPKM treatment. The digestion capacity of fish also slightly improved with both these dietary treatments, as indicated by the specific activities of trypsin and amylase (P > 0.05). Only the fish fed with SPKM were adapted to digest lipids as compared to the control. Significant improvements in the radical scavenging activity of stomach were observed with MPKM and SMPKM treatments, but the levels were unaffected in the liver and intestine. No negative effects were found on scavenging activity in the three organs, in fish fed SPKM diet as compared to the control. The carcass and muscle compositions were closely similar across the four dietary treatments, with only small improvements from the SPKM and the SMPKM diets in terms of carcass moisture and ash, and muscle protein and RNA/protein ratio. No differences were observed in the enthalpy responses of muscle actin and myosin between the four dietary treatments, but an inducible protein peak was found only in the fish fed with SPKM. Overall, these findings indicate that water soaking or soaking followed by microwave irradiation improved the nutritional quality of the PKM-containing diet. Practically, the simple low-cost modification by water soaking has wide application potential in the administration of aquafeed.