The role of predigested plant protein in enhancing nutritional value, feed utilization efficiency, and growth performance of Nile tilapia, Oreochromis niloticus

This study evaluated the effect of incorporating predigested Indigofera zollingeriana leaf meal as a partial substitute for soybean meal in the diet of Nile tilapia (Oreochromis niloticus) on feed utilization efficiency, protein efficiency ratio, growth performance, and survival rate. Predigestion was conducted using cellulase enzyme (1.2 g kg?¹) to hydrolyze complex fiber and protein compounds into more digestible forms. A Completely Randomized Design (CRD) was employed, with four dietary treatments: 0 (control), 25, 50, and 75% substitution of soybean meal with predigested Indigofera leaf meal, each containing 30% crude protein and an energy-to-protein ratio of 8.5-9.0 kcal g?¹. The feeding trial lasted six weeks using juvenile tilapia (2.39±0.12 g) stocked at a density of 50 fish m?² and fed three times daily to satiation. The results showed that predigestion enhanced the nutritional quality of Indigofera leaf meal, increasing protein content from 31.04 to 38.22% and reducing crude fiber from 15.53 to 13.10%. Increasing inclusion levels of predigested Indigofera leaf meal improved total feed intake (96.53-112.29 g), feed utilization efficiency (68.73-75.61%), protein efficiency ratio (2.29-2.52), and relative growth rate (4.22-5.84% day?¹). The highest final biomass (119.48 g) and survival rate (96.67%) were observed at the 75% substitution level, indicating that predigested I. zollingeriana meal supports efficient nutrient conversion and growth without adverse physiological effects. Water quality parameters, including temperature (24-28°C), pH (7.9-8.1), dissolved oxygen (3.5-4.7 mg L?¹), and ammonia (