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Restriction or ban on antibiotic administration in aquaculture encourages the development of environment-friendly feed additives as immunostimulants. Short-chain fatty acids (SCFAs) and their salts are 'Generally Regarded as Safe' and are often used as antimicrobials in the livestock feed industry. Formate, acetate, propionate, butyrate and their salts are among the most studied SCFAs in aquaculture. These SCFAs affect the host performance as well as physiological response upon three ways: either through effects of the feeds that are being administered, through effects on the gastrointestinal tract of the animal or through direct effects on metabolism. To date, most of the available data are focused on the effects of SCFAs on growth performance and feed utilization. Despite extensive research studies on the effects of the different type of SCFAs and their salts on growth performance and feed utilization, the effects of these feed additives on the health of aquatic organisms have only been receiving attention recently. The results of the studies demonstrated beneficial effects of SCFAs as promising feed additives in aquaculture. The present review article summarizes and discusses the topic of dietary administration of SCFAs and their salts in aquaculture with a closer look at the recent findings regarding the effects of SCFAs on growth performance and health status of fish and shellfish. Furthermore, this review identifies the gaps of existing knowledge regarding the roles of SCFAs in the growth and health status of aquatic animals and suggests research areas that merit further investigations.

In this study, we examined the effects of the following eight experimental diets, which varied in fructo oligosaccharides (FOS), mannan oligosaccharides (MOS) and Bacillus clausii concentrations, on the Japanese flounder: control diet (no FOS, MOS and B. clausii), diet F (5 g kg−1 FOS), diet M (5 g kg−1 MOS), diet FM (2.5 g kg−1 FOS + 2.5 g kg−1 MOS), diet B (107 cells g−1B. clausii), diet FB (5 g kg−1 FOS + 107 cells g−1B. clausii), diet MB (5 g kg−1 MOS + 107 cells g−1B. clausii) and diet FMB (2.5 g kg−1 FOS + 2.5 g kg−1 MOS + 107 cells g−1B. clausii). Japanese flounder, initially weighing an average of 21 g, were distributed into 24 net cages at a stocking density of 20 fish per cage. Each diet was hand‐fed to three groups of fish twice daily for 56 days. The weight gain rate (WGR) in fish fed diets B, MB and FMB were significantly higher than in fish fed the control diet, where the fish fed diet FMB had the highest WGR. Fish fed any of the diets, except diets F and B, exhibited better feed conversion ratio than those fed the control diet. Diets MB and FMB significantly elevated intestinal protease activity compared with the control diet, but only the diet FMB promoted amylase activity. Feeding diets FB and FMB increased body protein deposition; additionally, feeding diets B, MB and FMB significantly reduced body lipid deposition. Lysozyme (LSZ) activity was significantly higher in fish fed diets B, FB, MB and FMB than in fish fed the control diet. All diets, except diet M, decreased triglyceride (TG) levels compared to the control diet. Low‐density lipoprotein cholesterol levels in fish fed diets F, FB and FMB were significantly lower than in fish fed the control diet. Without exception, no diets affected feeding rate, condition factor, body moisture, ash contents, phagocytic activity of leucocytes or cholesterol or high‐density lipoprotein cholesterol levels. Our results suggest that diets supplemented with FOS, MOS and B. clausii improved growth performance and health benefits of the Japanese flounder more than other diets or the control diet.

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It is now a well-documented fact that there is a distinct relation between fish nutrition and health status. Intensification of aquaculture practice to meet market demand causes stress and elevates the risk of the disease outbreak. Therefore, provisions of proper diets as well as appropriate feeding regimens are of high importance in intensive aquaculture. Considering the negative impacts raised by prophylactic and therapeutic use of antibiotic in aquaculture, administration of dietary immunostimulant has been suggested as an alternative to antimicrobial agents. In this sense, functional dietary supplements, including pre-, pro-and synbiotic received increasing attention as an environment-friendly strategy for improving fish health. During the past years, administration of prebiotics in the diet of different fish species revealed promising results in immune response. In the present review article, the topic of the administration of dietary prebiotics in aquaculture is addressed with a special focus on recent findings regarding the effects of prebiotics on fish immune response and possible mode of action. Furthermore, the present study covers the gap in existing knowledge and suggests issues that merit further investigation.

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