The Effects of Dietary Supplement of Immunogen on Growth Performance, and Visceral and Hepatic Somatic Indices of Juvenile Rainbow Trout, Oncorhynchus mykiss (Walbaum 1792)

Prebiotics have been introduced as non-digestible feed ingredients, which stimulate growth and activity of beneficial bacteria. This study was conducted to evaluate the effects of Immunogen, a mixture of prebiotic on the growth performance and visceral and hepatic somatic indices in rainbow trout, Oncorhynchus mykiss (Walbaum 1792). A basal diet was formulated using common feed ingredients supplemented with Immunogen at 0, 1, 1.5, and 2 g.kg^-1, leading to four experimental diets. Each experimental diet was randomly assigned to triplicate 1,500 L tanks. Rainbow trout with an initial weight of 99.59±0.74 g were randomly distributed in the experimental tanks. Results showed that inclusion of dietary Immunogen significantly increased the final weight and specific growth rate (SGR) (p 0.01) of rainbow trout compared to the control. Feed conversion ratio (FCR) and protein efficiency ratio (PER) were also improved after prebiotic administration to the experimental fish (p 0.01 and 0.05, respectively). Dietary addition of 2 g.kg ^-1 prebiotic also increased the relative liver and visceral weights (p 0.05). The body composition and blood cortisol level were not influenced by the prebiotic inclusion (p 0.05). In conclusion, administration of the prebiotic Immunogen is capable of improving the nutrient efficiency and growth performance of rainbow trout confirming the positive effect of a mixture of prebiotics on the fish.