62 DECEMBER 2022 • WORLD AQUACULTURE • WWW.WA S .ORG system and resistance to disease. Yeast β-glucan activates the innate immune defence mechanisms by acting on receptors and triggering intracellular gene activation that produces antimicrobials. It increases phagocytic activity, complement activity, lysozyme, disease resistance and serum Ig level. β -1-3 glucan can also stimulate the non-specific immune system of crustaceans by stimulating the prophenol oxidase (proPO) system to eradicate invasive agents (Babu et al. 2013). Yeast cell wall is the main ingredient in most commercial immunostimulants used in aquaculture. Probiotic Probiotics are live microorganisms introduced in adequate amounts for improving the health of their host. The presence of diverse enzymes, polyamines, cell wall hydrophobicity and the ability to colonise in mucus makes yeast a good candidate as a probiotic. Yeast enhances growth and survival by gut maturation. Yeast administered to early developmental stages of fish larvae boosts growth and reduces mortality. In comparison with probiotic bacteria, yeast is resistant to antibiotics. A major problem with probiotic bacteria is the transfer of antibiotic-resistant genes to pathogenic bacteria, which can be avoided using probiotic yeast. Some commercially used probiotic yeast products include Aqualase® and Hydroyeast Aquaculture® (Khalil et al. 2012). Growth of rainbow trout is enhanced by dietary administration of Aqualase® (Adel et al. 2016). Antimicrobial Peptides Antimicrobial peptides (AMPs) are small proteins involved in the innate immune system and that have antimicrobial activity against bacteria, viruses and fungi. AMPs can alter the functions of biological membranes because of their specific biophysical properties and amino acid composition. Antimicrobial peptides work by inhibiting ATP and synthesis of nucleic acids and proteins in pathogenic organisms. Yeast is rich in antimicrobial peptides (Gyan et al. 2019). Yeast AMPs can inhibit fungi and Gramnegative and Gram-positive bacteria (Naimah et al. 2017). Conclusion Yeasts have been receiving increased attention as alternative protein sources in fish feeds. More studies are required to exploit the use of yeast in aquaculture. Yeast products are cost-effective and environment friendly. Applications of yeast-derived AMPs in aquaculture health management is promising. So far, only a limited number of strains have been studied. Yeast research in aquaculture has mainly concentrated on Saccharomyces cerevisiae. Several yeast species remain unexplored, especially in marine and mangrove habitats. The role of yeast in the gut microbiome of fishes is another promising area for research. Notes Elina Jose Vettom, Susan Shibu and Rejish Kumar V.J Faculty of Fisheries, Kerala University of Fisheries and Ocean Studies, Panangad, Kochi 682506, India. rejishkumar@gmail. com References Adel, M., C.C. Lazado, R. Safari, S. Yeganeh and M.J. Zorriehzahra. 2017. Aqualase®, a yeast-based in-feed probiotic, modulates intestinal microbiota, immunity and growth of rainbow trout Oncorhynchus mykiss. Aquaculture Research 48(4):1815-1826. Ahmadi, A., M.T. Mozanzadeh, N. Agh and M.N. Bahabadi. 2017. Effects of enriched Artemia with Saccharomyces cerevisiae and Chaetoceros gracilis on growth performance, stress resistance and fatty acid profile of Litopenaeus vannamei postlarvae. Journal of Fisheries and Aquatic Studies 5(2):669-673. Babu, D.T., S.P. Antony, S.P. Joseph, I.S.B. Singh and R. Philip. 2013. Marine yeast Candida aquaetextoris S527 as TABLE 1. Yeast and its beneficial properties. Yea s t s pe c i e s Pr ope r t i e s Re f e r enc e Saccharomyces cerevisiae Improved immunity and growth Adel et al. 2017 Saccharomyces elipsoedas Probiotic; modulated intestinal microbiota, Adel et al. 2017 improved immunity and growth performance. Saccharomyces boulardii Antimicrobial; inhibition activity against 26 isolates of bacteria. Naimah et al. 2018 Debaryomyces hansenii Probiotic; improved immune and antioxidant systems Navarrete et al. 2014 in fish larvae and juveniles. Phaffia rhodozyma Source of astaxanthin pigment. Johnson et al. 1980 Candida utilis Antimicrobial activity; inhibition of growth of pathogens, enhanced innate immune system and improved disease resistance. Gyan et al. 2019 Candida aquaetextoris Improved immune parameters; better protection Babu et al. 2013 against WSSV infection. Candida sake Enhanced growth and survival rate in shrimp. Ernesto Ceseña et al. 2021
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