The study was performed to determine the effects of FARMARIN (R) XP and INFISH-AQUA (R) on growth performance, proximate composition, biometric indices, serum biochemical variables, hematological parameters, non-specific immune responses, digestive enzyme activities and disease resistance of rainbow trout (Oncorhynchus mykiss) juveniles against Yersinia ruckeri. Four experimental groups of fish were fed an additive free basal diet (control) and FARMARIN (R) XP incorporated test diets at increasing levels (0.1%-F1, 0.2%-F2, 0.4%-F4) for 60 days. Additionally, a fifth group of test diet was antibiotic medicated (0.1%), prepared with the commercial product INFISH-AQUA (R) (sulphadiazine 20% and trimethoprim 4%). When fish were challenged with Yersinia ruckeri after the 60-days feeding trial, and mortality was recorded over an additional 20-days period, no influence of FARMARIN (R) XP and antibiotic supplemented diets were observed on growth performance and hematological parameters of rainbow trout. However, the intestinal lipase activities in Fl, F2 and AMF groups were significantly higher than the other treatments. Serum glucose level was significantly lower in the F4 group, and triglyceride levels decreased significantly when fish were fed with FARMARIN (R) XP or antibiotic supplemented diets. The dietary FARMARIN (R) XP especially at 0.1% and 0.2% significantly increased the respiratory burst activity. A decreasing potential killing activity and phagocytic index were found in the F4 and AMF groups. At the end of the 20-day challenge period the survival rates were significantly higher in the F2 and AMF groups compared to all other treatment groups. Thus FARMARIN (R) XP can be used as a replacement for antibiotic in rainbow trout diets for the control of yersiniosis.