S.A Hosseini - Department of Fisheries, Faculty of Marine Natural Resources, Khorramshahr University of Marine Science and Technology. Khorramshahr, Iran
P Kochanian - Department of Fisheries, Faculty of Marine Natural Resources, Khorramshahr University of Marine Science and Technology. Khorramshahr, Iran
M Alishahi - Department of Clinical sciences, Faculty of Veterinary Medicine, Shahid Chamran University of Ahvaz, Ahvaz- Iran
T Mohammadian - Department of Clinical sciences, Faculty of Veterinary Medicine, Shahid Chamran University of Ahvaz, Ahvaz- Iran
M Zakeri - Department of Fisheries, Faculty of Marine Natural Resources, Khorramshahr University of Marine Science and Technology. Khorramshahr, Iran

The application of probiotics in aquaculture has been increased in recent years due to the many benefits for fish health. Encapsulation of probiotics within biodegradable nanoparticles has been found to increase their viability and efficiency in fish gut. In the current study, the effects of encapsulation of Lactobacillus rhamnosus by alginate/chitosan on growth performance and digestive enzymes activity in rainbow trout (Oncorhynchus mykiss) were evaluated.An experiment was designed with five treatments each with three replicates. ۶۰۰ juvenile O. mykiss average (±SD) initial weight of ۲۵.۵۳±.۸۲ g was assigned to fifteen experimental tanks. Fish in T۱ received Lactobacillus rhamnosus encapsulated by Ionic gelation, fish in T۲ received L rhamnosus encapsulated by internal emulsification, T۳ were fed with alginate/chitosan enriched free probiotic diet, T۴ received bacteria without any encapsulation and T۵ received a basic diet as a control group. Fish were fed with experimental diets for ۶۰ days and the study continued for a further ۱۵ days with basic diet in all treatments. Fish were sampled on days ۳۰ and ۶۰ and growth performance indices (FCR, PER, SGR, CF, and WGP) and digestive enzymes activity (lipase, protease, trypsin and chymotrypsin) were compared among the treatments. Most of growth indices in treatment ۲ had a significant improvement compared to other treatments. The lowest FCR (۰.۹۳±۰.۰۳) at day ۳۰ was seen in T۲ which was significantly different from control treatment (p<۰.۰۵). PER values at days ۳۰, ۶۰ and CF at day ۶۰ were higher in T۱ and T۲, that this increase was significant in T۲ than control group (p<۰.۰۵). It can be concluded that the microencapsulation of Lactobacillus rhamnosus by internal emulsification with alginate/chitosan has significant effects on some of growth performance and digestive enzymes activity in rainbow trout and the use of this method to improve the performance of the probiotic in rainbow trout is recommended.

Probiotic potential, Immunostimulation, Lactobacillus rhamnosus, Microencapsulation, Alginate/ chitosan, Rainbow trout