Aquaculture is one of the fastest growing industries in the world. The need for enhanced disease
resistance, feed efficiency, and growth performance of cultured organisms is substantial for various
sectors of this industry. If growth performance and feed efficiency are increased in commercial
aquaculture, then the costs of production are likely to be reduced. Also if more fish are able to
resist disease and survive until they are of marketable size, the subsequent cost of medication and
overall production costs would be reduced drastically. It has been documented in a number of food
animals that gastrointestinal microbiota play important roles in affecting the nutrition and health
of the host organism. Thus, various means of altering the intestinal microbiota to achieve favorable
effects such as enhancing growth, digestion, immunity, and disease resistance of the host organism
have been investigated in various terrestrial livestock as well as in humans. Dietary supplementation
of prebiotics, which are classified as nondigestible food ingredients that beneficially affect the host
by stimulating growth and/or activity of a limited number of health-promoting bacteria such as
Lactobacillus and Bifidobacter spp. in the intestine, while limiting potentially pathogenic bacteria
such as Salmonella, Listeria and Escherichia coli, have been reported to favorably affect various
terrestrial species; however, such information is extremely limited to date for aquatic organisms.
Effects of probiotics, defined as live microbial feed supplements, on gastrointestinal microbiota have
been studied in some fishes, but the primary application of microbial manipulations in aquaculture
has been to alter the composition of the aquatic medium. In general, the gastrointestinal microbiota
of fishes including those produced in aquaculture has been poorly characterized, especially the
anaerobic microbiota. Therefore, more detailed studies of the microbial community of cultured fish
are needed to potentially enhance the effectiveness of prebiotic and probiotic supplementation. This
review summarizes and evaluates current knowledge of intestinal microbial ecology of fishes, the
various functions of this intestinal microbial community, and the potential for further application
of prebiotics and probiotics in aquaculture.