The dietary effects of rosemary (Rosmarinus officinalis) leaves powder (RLP) were tested on the performance and welfare of Nile tilapia (Oreochromis niloticus) fingerlings subjected to lead (Pb) toxicity. Two hundred fish (31.9±0.28 g) were stocked into 20 85-L glass aquaria (10 fish/aquarium) to represent four treatments with five replicates each. Fish were fed on 0.0% (control; T1) and 1.0% RLP (T2) along with continuous exposure to either 0.0 (T3) or 7.94 mg Pb/L (T4) for 60 days. Compared with the control diet, feeding Nile tilapia on RLP alone improved the growth performance and hemato-biochemical, antioxidant, and immunological indices. Conversely, the Pb toxicity negatively affected hematocrit, hemoglobin, white and red blood cell counts, and growth indices. Furthermore, Pb exposure raised blood cortisol, glucose, total cholesterol, serum transaminases (ALT and AST levels), alkaline phosphatase, and lactate dehydrogenase accompanied with significant reductions in serum total lipids, protein, albumin, and globulin values. Furthermore, Pb exposure decreased respiratory burst, lysozyme, total immunoglobulins, malondialdehyde, superoxide dismutase, catalase, and total antioxidant capacity. On the other hand, dietary RLP significantly reduced the negative impacts of Pb toxicity on the above-mentioned indices. Additionally, the dietary RLP reduced the Pb accumulation in Pb-intoxicated fish leading to significant enhancements in Nile tilapia’s growth and welfare. These findings suggest that dietary 1% RLP significantly enhanced the fish performance and welfare status and could alleviate the Pb toxicity effects on Nile tilapia performance and welfare.
