Evaluation of Propylene Glycol and Essential Oil Supplementation on Growth Performance, Feed Efficiency, Serum Biochemical Indices, Hematological Parameters, and the Expression of Antifreeze IV and Lipid Metabolism-Related Genes in Nile Tilapia

Aquaculture output, sustainability, and profitability can be enhanced by using functional feed additives. The effect of supplementation with two different dietary levels of propylene glycol (PG) and essential oils (EOs) was evaluated in Nile tilapia. A total of 150 juvenile fish were randomly allocated into five groups. Growth performance, feed utilization, serum biochemistry, hematology, and gene expression were assessed. PG supplementation significantly improved growth performance, feed conversion, protein efficiency, and energy utilization. Both additives significantly reduced cortisol and glucose levels and altered liver enzymes and lipid profiles. PG improved immunological indices, while hematological responses were dose-dependent; both EOs and PG increased hematocrit, mean corpuscular volume (<i>MCV</i>), and mean corpuscular hemoglobin (<i>MCH</i>). Moreover, the high PG dose significantly increased platelet counts, reduced hemoglobin (Hb), and elevated hematocrit. Additionally, EOs significantly upregulated antifreeze protein IV (<i>AFPIV</i>) and fat metabolism-related genes in a dose-dependent manner, indicating a potential role in lipid mobilization and stress tolerance. Expression analysis of the immunoglobulin H (<i>IGMH</i>) gene revealed a significant increase in PG-supplemented groups, suggesting its immunostimulatory potential. Overall, PG enhanced immunity and growth performance, while EOs promoted <i>AFPIV</i> and fat metabolism gene expression. Therefore, PG and EO supplementation could serve as an effective functional strategy to enhance <i>O. niloticus</i> growth, stress adaptation, and immune resilience.