University of Guilan Caspian Journal of Environmental Sciences 1735-3033 2024 11 13 Effects of selenomethionine and synbiotic Diproplus (Dip+) on growth, hematology, carcass analysis, some immune parameters and IL-1 and TNF-α relative genes expression in Salmo caspius 1 17 8151 10.22124/cjes.2024.8151 EN Maziyar Akbarabadi Department of Fisheries, Lahijan Branch, Islamic Azad University, Lahijan, Iran Hossein Khara Department of Fisheries, Lahijan Branch, Islamic Azad University, Lahijan, Iran Habib Vahabzadeh Roudsari Department of Fisheries, Lahijan Branch, Islamic Azad University, Lahijan, Iran Mohaddeseh Ahmadnezhad Inland Waters Aquaculture Research Center, Iranian Fisheries Sciences Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Bandar Anzali, Iran Roghieh Safari Department of Aquaculture, Faculty of Fisheries and Environmental Sciences, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran Journal Article 2024 11 13 Limited research has focused on the nutritional requirements of <em>Salmo caspius</em>. This study investigates the effects of Selenomethionine (SelMet) and synbiotic Diproplus (Dip+) oral supplements on growth, hematology, carcass analysis, immune responses, and the IL-1 and TNF-α relative gene expression in <em>S. caspius</em>. By employing a randomized design, the dietary control group and various treatments (per kg of diet) were established, including T₁ (2 g Dip⁺ + 0 mg SelMet), T₂ (3 g Dip⁺ + 0 mg SelMet), T₃ (0 g Dip⁺ + 2 mg SelMet), T₄ (0 g Dip⁺ + 4 mg SelMet), T₅ (2 g Dip⁺ + 2 mg SelMet), T₆ (2 g Dip⁺ + 4 mg SelMet), T₇ (3 g Dip⁺ + 2 mg SelMet) and T₈ (3 g Dip⁺ + 4 mg SelMet). Significant increases in growth performance and the highest lysozyme activity were observed in T₆ (<em>p</em> < 0.05). T₃ and T₇ showed the highest total Ig and IgM levels, respectively (<em>p</em> < 0.05).  Additionally, T₈ exhibited significantly elevated WBCs, RBCs, Hb, and Hct (<em>p</em> < 0.05). Carcass analysis indicated that the control group had the highest fat content and lowest amounts of ash, protein, and moisture (<em>p</em> < 0.05). Furthermore, the IL-1 and TNF-α relative gene expression levels increased approximately 16 and 22 times in T₈, respectively (<em>p </em>< 0.05). The findings suggest that the combined use of Dip⁺ and SelMet yields superior results compared to their individual use. We recommend combining 4 mg SelMet and 3 g Dip⁺ in fish farms. https://cjes.guilan.ac.ir/article_8151_f927efd08503a38abc34abec4b1399c2.pdf