Effects of chitosan-coated diet on improving water quality and innate immunity in the olive flounder, Paralichthys olivaceus

The majority of aquaculture farms in South Korea currently use a moist pellet (MP) based on a mixture of frozen fish and fishmeal as a feed source for marine-culture fish species. MP has been associated with several problems, including the deterioration of water quality and fish diseases on fish farms, owing primarily to the rapid collapse of MP in seawater. In order to circumvent those problems, we have developed a chitosan-based biopolymer coating material for the environment-friendly use of MP on aquaculture farms. The chitosan-coated MP diet was shown to improve water quality as compared to the non-coated MP diet in the fish farm environment. It resulted in reduced COD (chemical oxygen demand) and SS (suspended solid) values, as compared to the control. The fish fed with the chitosan-coated MP diet for 12 weeks manifested no significant differences in final body weight. However, some immune responses, including myeloperoxidase (MPO), neutrophil respiratory burst, and skin mucus lysozyme activity were significantly (p < 0.05) stimulated as compared to the non-coated MP diet fed fish. However, we noted no significant differences in the NBT reduction in blood (p > 0.05). In addition, the fish fed with chitosan-coated diets evidenced significant (p < 0.05) alterations in some hematological parameters, including AST, hemoglobin, HDL-cholesterol, and LDL-cholesterol. In this study, we noted a clear trend in that olive flounders fed with the chitosan-coated MP diet evidenced positively increased non-specific immune responses, in addition to an improvement in the water quality of the fish tank.