Plant mucilage, like quince seed mucilage, as a polysaccharide, has a wide range of useful properties such as anti-stress, antibacterial and increasing growth and immunity. This study investigated the effect of quince mucilage on immunology, hematology and virus resistance (IHNV) in fingerling rainbow trout with an average weight (mean ± standard error) of 2±0.2 g. For this purpose, all treats were fed at 3% of body weight for 60 days. Experimental treatments included a control (no quince mucilage), 1%, 3%, 6% and 9% quince seed mucilage treatments. The growth, hematology, noecific immunological parameters was investigated at the end of the experiment (day 60). Also, relative percent survival (RPS) was evaluated after the exposure to Infectious Hematopoietic Necrosis Virus (IHNV). In general, the results showed that the effect of food treatment of 9% mucilage on feed conversion ratio (FCR), final weight and body weight gain was significant (P 0.05). The difference in noecific immune system parameters including lysozyme activity and alternative complement pathway activities in diets containing 6% and 9% mucilage, and bactericidal activity in all mucilage treatments was significant compared to the control group (P 0.05). Respiratory burst activity in all diet containing mucilage had a significant difference with the control group (P 0.05). Also, the hematological parameters showed significant differences (P 0.05) between the control and the treatments containing mucilage. Determination of relative percentage survival (RPS) and cumulative mortality rate (CPM) after exposure to IHNV virus showed that all treated mucilage did not have a protective effect against the virus compared to the control group. In general, the results of study indicate that the diet containing quince seed mucilage improved growth performance and increased immunological and hematological parameters of the fingerling rainbow trout compared to the control group. Therefore, quince seed mucilage can be introduced as a useful food additive and immune stimulant in juvenile rainbow trout. Keywords : quince seed mucilage, immunology, rainbow trout,
