In intensive aquaculture system, farmed fishes are more prone to inevitable stress and ultimately to various diseases. To overcome this, immunomodulation of cultured fishes by dietary manipulation offers viable sustainable alternative to reduce the use of antibiotic, drugs, pesticides, hormones and other chemicals which in turn increases the residual load in the aquatic environment. A variety of immonostimulants especially bacterial polysaccharides have been in vogue to enhance the nonspecific immunity in fishes. Levan, a type of fructan is a non-digestible food fibre, consisting of β (2-6) linkages, found in the cell walls of plants, fungi and bacteria. The present book provides details account on the effect of microbial levan on growth performance and physio-biochemical responses in one of the important tropical freshwater fish, Labeo rohita. The wealth of valuable information generated on the impact of levan, would have wider significance for its future use in aquaculture sector as potent immunonutrient and ideal prebiotic. I wish this book would be of immense benefit to researchers, scientists, students entrepreneurs and fishers working in the field of aquaculture.