Population explosion and decreased agricultural productivity accompanied by increased global food demand. Due to rapid industrialization and real estate development lands under cultivation are decreasing day by day. In present scenario to feed enormous populations focus on seafood and it is predicted that by 2020 half of world seafood demand would be contributed by aquaculture. Thus more emphasis to increase aquaculture productivity is now on priority to fulfill increased global food demand. Application of probiotic bacteria can play major role in development of sustainable aquaculture.
Probiotics are microbial feed supplement which beneficially affects the host animal by improving its intestinal balance. These microbial cells that are administered and enter to gastrointestinal tract, survive there for improving health of fish. There are several reports about the use of probiotics in aquaculture water to regulate microflora, enhance the decomposition of the undesirable organic substances and improve ecological environment of aquaculture. In addition, their use can increase the population of food organisms and improve the immunity of cultured animals against pathogenic. These contribute to host health by enhancing their ability to digest and assimilate nutrients, antagonistic towards pathogens or by competing for nutrients, oxygen and attachment sites, direct uptake of dissolved organic material mediated by bacteria and enhancement of cellular or humeral immune response against pathogenic microorganisms. The degradation of comparatively unattractive complex molecules releases compounds that could be beneficial to the host.
Probiotics improve host digestive processes by producing extra cellular enzymes such as amylase, protease, cellulase and lipases as well as necessary growth factors. The probiotics produce extracellular amylase and protease is improved host carbohydrate and protein digestion, while cellulase and lipases producing probiotics improve cellulose and lipid digestion. Degradation of chitin, starch, protein, cellulose and lipids is largely due to the production of extra cellular enzymes; proteases, lipases, chitinases and cellulases by bacteria associated with aquacultures species. Several workers have reported that bacteria from isolated from fish can digest chitin, starch, protein, cellulose and lipids. Vitamins, carotenoids, short-chain fatty acids and lipids produced by probiotics that also contribute to the improve host nutrition. These are produced as secondary metabolites by probiotic bacteria. Carotenoids, which act as antioxidants and polyunsaturated fatty acids contribute significantly to the total fatty acid content of host fish.
Effective probiotics bacterial strains are selected based on ability to antagonize host pathogens, non pathogenic to host, ability to survive in the gastrointestinal tract of host (resistant to bile salt, low pH and proteases), producing extra cellular enzymes beneficial to host and availability in low cost. However, information regarding the extracellular enzyme producing intestinal bacteria from herbivores fish, their source and significance is scare. In this direction their role in sustainable aquaculture, in the research currently focuses on to isolate and characterize extracellular amylase, protease, cellulase and lipase producing bacteria and would facilitate the formulation of cost-effective probiotic along with fish diets to the development of sustainable aquaculture productivity.
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