Opoka minerals as a feed additive for Nile tilapia (Oreochromis niloticus): effects on physiology, immunity, and meat quality

Abstract This study evaluated the potential of Astrakhan (AR)-Opoka, a siliceous sedimentary rock (86.33 wt% silicon dioxide, ) as a sustainable functional mineral feed additive for Nile tilapia. Three replicate tanks (15 fish each) were assigned to diets supplemented with 0%, 2%, or 4% AR-Opoka-derived mineral premix for 10 weeks. The Opoka powder exhibited low moisture content (≈ 0.8–1.2%) and remained physically stable during storage, confirming its suitability for dietary inclusion. Supplemented groups showed reduced hemoglobin levels and increased counts of leukocytes. Elevated total protein, globulin, and triglyceride concentrations were observed, with dose-dependent modulation of low-density lipoprotein (LDL). Immunologically, lysozyme activity and IL-10 gene expression were significantly upregulated. In Opoka-treated groups, meat quality assessment revealed lower bacterial loads; undetected Salmonella , Listeria monocytogenes , and Staphylococcus aureus . Chemical freshness indices showed that histamine, total volatile basic nitrogen (TVB-N), and thiobarbituric acid reactive substances (TBARS) below international limits; in addition to higher protein content and lower moisture. Overall, AR-Opoka emerges as a cost-effective, environmentally friendly alternative to synthetic mineral premixes in aquaculture. To our knowledge, this is the first study to demonstrate the functional and immunomodulatory potential of AR-Opoka in tilapia. Future research should evaluate long-term bioavailability, safety, and commercial scalability.