Cellobiose are a group of cello- oligosaccharides that are linear and composed of two glycopyranose units. It is derived from the renewable, and low cost biomass from the forest farming residues and forest industry by-products. In general, cello oligosachharides have demonstrated beneficial effects on digestibility and intestinal ecology of animals. They have been shown to enhance the growth of lactic acid bacteria and its use as prebiotic has been suggested. Eventually, cellobiose produced from the most abundant carbon source lignocellulose can be an attractive novel additive in fish feed industries. Therefore, the aim of the project is to observe the effect of different levels of COS on the distal intestine microbiota.