Effects of Ulva lactuca as a dietary supplement on growth, antioxidants and digestive enzymes of Nile tilapia (Oreochromis niloticus) under intermittent fasting and regular feeding regimes in the recirculating system

This study evaluated the effects of dietary supplementation with Ulva lactuca (5% = ULM5; 10% = ULM10) on Nile tilapia (Oreochromis niloticus) under prolonged intermittent fasting (1 week fasting/1 week feeding for 12 weeks). While fasting reduced growth and body composition parameters, protein content remained above 20% across all groups. ULM5 improved growth performance under normal feeding, whereas ULM10 enhanced antioxidant defense [up arrow SOD (superoxide dismutase), up arrow CAT (catalase), down arrow LPO (lipid peroxidation)], particularly during stress. Digestive enzyme activities declined during fasting but recovered in U. lactuca-fed groups. These findings suggest that U. lactuca, especially at 10%, may support physiological resilience and oxidative balance during nutritional stress, highlighting its potential as a functional feed additive in sustainable aquaculture.