ARTICLE FEED & ADDITIVE MAGAZINE January 2024 59 step of colonisation of the gut. Therefore, supplementation of mannose in basal feed of animals may contribute to better health by interfering with colonisation and growth of pathogens in the gut. INDIGESTIBLE OLIGOSACCHARIDES Certain indigestible oligosaccharides are not digested in the upper part of the gastrointestinal tract, but are selectively fermented by bacteria like Bifidobacteria Lactobacilli and Bacteroides in the colon and promote the growth of these beneficial bacteria which in turn confer health benefit to host. Thus, these natural feed ingredients act as prebiotics. They include resistant inulin and oligofructose, transgalacto-oligosaccharides (TOS), mannan oligosaccharide (MOS) and lactulose. Role of Indigestible oligosaccharides or prebiotics in fish nutrition Prebiotic supplementation in fish feed may help in changing the community of bacteria in gastrointestinal tract, improving immune system and increasing growth rate. 1. Effects of prebiotics on immune system Prebiotics can modify the GI tract microbial community to enhance non-specific immune responses. Indigestible oligosaccharides serve as substrate for the growth and proliferation of anaerobic bacteria, mainly the Bifidobacteria and are fermented by these bacteria in the caeco-colon region. During fermentation of prebiotics by beneficial bacteria (probiotics), short chain fatty acids (SCFA) are produced which cause acidification of the colonic content (or reduction of gut pH). Lower pH values inhibit the growth of certain pathogenic bacterial species while stimulating the growth of the Bifidobacteria and other lactic acid species. Other changes include secretion of antimicrobial substances; blocking of adhesion sites; attenuation of virulence; blocking of toxin receptor sites; competition for nutrients, and suppression of toxin production. These changes in GIT altogether stimulate the immune system, thus, enhancing the host’s protection against infections. 2. Prebiotic may have the role of supplying energy for the host Prebiotics are selectively fermented by probiotic bacteria e.g. Bifidobacteria, Lactobacillus and Bacteroides to produce short chain fatty acids (acetate, butyrate, propionate) and lactate. Short chain fatty acids are absorbed through the intestinal epithelium and act as an energy source for the host, whereas lactate enters the liver and is used as precursor for gluconeogenesis. 3. Effect on mineral absorption Minerals such as calcium, magnesium and iron are not absorbed in the small intestine and so reach the colon, where upon fermentation of prebiotics, they are released from the carbohydrate matrix and are absorbed. References 1. Sinha, A. K., Kumar, V., Makkar, H.P., De Boeck, G., & Becker, K. (2011). Non-starch polysaccharides and their role in fish nutrition – A review. Food Chemistry, 127(4), 1409-1426. 2. Yousefian, M., & Amiri, M.S. (2009). A review of the use of prebiotic in aquaculture for fish and shrimp. African Journal of Biotechnology, 8(25). 3. Wee, W., Hamid, N. K. A., Mat, K., Khalif, R. I. A. R., Rusli, N. D., Rahman, M. M., ... & Wei, L. S. (2022). The effects of mixed prebiotics in aquaculture: A review. Aquaculture and Fisheries. Figure 1. Effects of mixed prebiotics in aquaculture species. Source: (Wee et al. 2022)
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