Agricultural Research,Education and Extension Organization Iranian Journal of Fisheries Sciences 1562-2916 24 6 2025 11 01 Therapeutic advantages of gamma irradiated propolis in mitigating the risk of Ichthyophthirius multifiliis infection in rainbow trout (Oncorhynchus mykiss) 1327 1347 134483 10.22092/ijfs.2025.134483 EN M. Heidarieh Nuclear Science and Technology Research Institute, Tehran, Iran M. Banaee Aquaculture Department, Faculty of Natural Resources and the Environment, Behbahan Khatam Alanbia University of Technology, Behbahan, Iran H. Heidarieh Division of Aquatic Animal Health, Department of Clinical Sciences, School of Veterinary Medicine, Shiraz University, Shiraz, Iran A. Gholamhosseini Division of Aquatic Animal Health, Department of Clinical Sciences, School of Veterinary Medicine, Shiraz University, Shiraz, Iran C. Faggio Department of Chemical, Biological, Pharmaceutical and Environmental Sciences, University of Messina, Messina, Italy Journal Article 2025 09 29 This study investigated the effects of irradiated-propolis (GI-EEP) supplementation on rainbow trout (<em>Oncorhynchus mykiss</em>) during an <em>Ichthyophthirius multifiliis</em> (Ich) challenge, aiming to determine if it could enhance the fish immune system and improve its response against Ich. In this experiment, 150 fish (35.80±3.95 g) were divided into five groups and fed diets containing gamma-irradiated or non-irradiated propolis extracts or no treatment (control) for 60 days. The fish were then challenged with 5000 <em>I. multifilis</em> theronts per fish. Then, five days post-challenge, blood and skin samples were taken for hematological, biochemical, and gene expression analysis. The results showed that 0.5 g kg^-1 of gamma irradiated- ethanol extract propolis (GI-EEP) supplementation regulated electrolyte levels, improved blood biochemical parameters, and enhanced the immune system's response in Ich-infected rainbow trout. It increased lysozyme activity, elevated white blood cell counts, and improved red blood cell counts. Supplementation with GI-EEP positively influenced these parameters, including increasing total protein and albumin and decreasing globulin levels. It also elevated alkaline phosphatase activity, indicating improved inflammation control. Gene expression analysis revealed increased levels of inflammatory and immune response markers, including interleukin 8, and immunoglobulin M. No significant changes were observed in C3 complement mRNA gene expression levels. Elevated major histocompatibility complex II mRNA levels indicated an effective immune response. Overall, administering IPE to Ich-infected rainbow trout regulated electrolytes, improved blood parameters, and boosted the immune system's ability to combat the infection. Results showed that the optimal propolis dose for regulating physiological parameters and immune responses in Ich-exposed fish was 30 KGy. https://jifro.areeo.ac.ir/article_134483_570722b861b0423130c2170ddbde8151.pdf