Effects of Immunostimulants, Prebiotics, Probiotics, Synbiotics, and Potentially Immunoreactive Feed Additives on Olive Flounder (Paralichthys olivaceus): A Review

Prebiotics, probiotics, and synbiotics are considered natural functional food ingredients and an alternative feeding strategy for immunomodulation and antibiotic eradication. Olive flounder (Paralichthys olivaceus) is commercially cultured in China, Japan, and Korea. Antibiotics used in flounder aquaculture produce antibiotic-resistant pathogens and residual effects on human. Prebiotics are non-digestible oligosaccharides, fermented by intestinal microbiota to produce short-chain fatty acids that bind G protein receptors. Probiotics are usually incorporated into the diet at a certain concentration to alter the intestinal microbial population through colonization or implantation. Synbiotics are combinations of prebiotics and probiotics that produce synergistically better benefits than separately. Previous studies on olive flounder have revealed that various types of immunostimulants, prebiotics, probiotics, synbiotics, and potentially immunoreactive feed additives can increase growth and feed utilization; cellular and humoral immunity; immune gene expression; blood/serum biochemistry; and infectious-disease resistance. Additive concentrations, their activity, and viability after feed storage and in the intestine, and interactions with the intestinal microbial community are major limiting factors. This review summarizes and discusses changes in growth and feed utilization, innate immunity, biochemical parameters, gene transcription, and disease protection in olive flounder after diet supplementation with various types of additives. It also indicates areas needing greater attention for future research.