Digestive Enzyme Activity as a Biological Indicator for Assessing the Sustainability of Biofloc and Non-Biofloc Systems in the Nile Tilapia (Oreochromis niloticus) Culture

Digestive enzyme activity represents a valuable biological indicator for assessing the sustainability of aquaculture systems since it reflects nutrient utilization efficiency, metabolic adaptation, and the ecological performance of cultured species. This study compared the Nile tilapia (Oreochromis niloticus) reared in biofloc and conventional (non-biofloc) systems over 3–5 months by analyzing protease, cellulase, and lipase activities, growth performance, and water quality. Protease activity was significantly higher in biofloc fish at 3 months (1.688 ± 0.03 vs. 1.437 ± 0.10 U/mL/min, P< 0.05), while cellulase activity showed no statistical differences between systems. Lipase activity was consistently higher in non-biofloc fish (4.8–5.3 vs. 2.8–3.8 U/mL/min, P< 0.05), suggesting reduced reliance on endogenous lipid digestion under biofloc conditions due to microbial enzyme contributions. Growth performance revealed higher specific growth rates (SGR) in biofloc fish (2.06% vs. 1.83% per day at 3 months; 1.53% vs. 1.45% at 5 months), though both remained below the optimal range. Water quality parameters were within acceptable limits, with biofloc systems showing stable pH (6.1–8.0) and sufficient dissolved oxygen (5.1–6.9 ppm), while conventional systems maintained higher DO (8.0–10.7 ppm) but greater alkalinity fluctuations. Overall, the findings highlight that biofloc technology enhances early digestive efficiency, supports sustainable growth, and reduces environmental discharge through nutrient recycling, confirming its potential as a more eco-efficient system for the Nile tilapia culture.