Dietary Proline Enhances Physiological Adaptation and Oxidative Stress Resistance in Nile Tilapia Cultured Under Chronic Salinity Stress

Saline tilapia farming is expanding in coastal aquaculture; however, chronic salinity exposure induces osmotic and oxidative stress that impairs growth and physiological stability. This study evaluated the effects of dietary L-proline as a functional osmoprotective amino acid on Nile tilapia reared under chronic salinity stress. Juvenile red tilapia (3.66±0.08 g) were cultured at 25 ppt for 60 days and fed four isonitrogenous diets containing 0, 4, 8, or 12 g kg⁻¹ proline. Dietary proline significantly improved growth and feed efficiency, with weight gain increasing from 23.65±0.43 g in the control group to 25.51–27.20 g in proline-supplemented groups and specific growth rate increasing from 3.35±0.09 to 3.48–3.53% BW day⁻¹. Feed conversion ratio decreased from 1.24 in the control to 1.09–1.11 in supplemented groups. Hematological indicators revealed improved physiological status, with reduced erythrocyte and leukocyte counts. Antioxidant capacity increased, with superoxide dismutase activity rising up to 2.4-fold, while catalase showed moderate enhancement. Gill histology showed reduced hyperplasia and lamellar deformation. Although fillet proximate composition was not significantly affected, fillet protein remained stable at 20.71–21.27%. These findings identify dietary L-proline as a functional nutritional strategy for improving salinity resilience in Nile tilapia.