Lactoferrin supplementation mitigates high-density stress in Oreochromis niloticus

This study examined how dietary lactoferrin supplementation affected growth, water quality, hematological and biochemical parameters, antioxidant status, liver histology, and immunological responses in Oreochromis niloticus raised at two stocking densities. A total of 360 fingerlings (10.17 ± 0.13 g) were divided into a 2 × 4 factorial design with two stocking densities (SD10: 10 fish per aquarium; SD20: 20 fish per aquarium) and four dietary lactoferrin concentrations (0, 200, 400, and 600 mg kg⁻¹ diet), with three aquaria per treatment, for 60 days. Dietary lactoferrin supplementation significantly enhanced growth performance, feed utilization, and survival, with the greatest improvements observed at 600 mg kg⁻¹ diet. Lactoferrin supplementation increased hemoglobin levels, red blood cell and platelet counts, while modulating leukocyte profiles by reducing stress-induced leukocytosis and neutrophilia and increasing lymphocyte proportions, particularly under high stocking density (SD20). AST activity, creatinine, glucose, and cortisol levels were elevated in fish reared at SD20, while dietary lactoferrin reduced liver enzyme activities and stress biomarkers in a dose-dependent manner. IgM, lysozyme, SOD, CAT, and GPX activities were markedly increased, while MDA levels were decreased by dietary lactoferrin at 600 mg kg⁻¹ diet. Histological examination revealed normal liver architecture in all groups, with enhanced hepatocellular activity and well-organized hepatic structures in lactoferrin-supplemented fish, without any pathological alterations. In conclusion, dietary lactoferrin at 600 mg kg⁻¹ alleviated the detrimental effects of high stocking density by enhancing growth, physiological condition, antioxidant capacity, immunological responses, and liver health in Nile tilapia.