Effects of prebiotics on growth performance, nutrient utilization and the gastrointestinal tract microbial community of hybrid striped bass (Morone chrysops x M. saxatilis) and red drum (Sciaenops ocellatus)
A series of experiments examined the effects of four potential prebiotics-- GroBiotic?-A (a mixture of partially autolyzed brewers yeast, dairy components and dried fermentation products), mannanoligosaccharide (MOS), galactooligosaccharide (GOS), and inulin/ fructooligosaccharide (FOS)--on the gastrointestinal (GI) tract?s microbial community in hybrid striped bass and red drum. The first in vitro experiment applied denaturing gradient gel electrophoresis (DGGE) to examine responses of red drum GI tract microbiota to anaerobic incubation with brewers yeast, FOS, and GroBiotic?-A. Brewers yeast and GroBiotic?-A produced unique microbial communities compared to that associated with the basal diet. Volatile fatty acid (VFA) profiles did not differ among treatments, with acetate being the major fermentation product. A second in vitro experiment examined effects of GroBiotic?-A, MOS, GOS, and FOS on the GI tract microbiota of hybrid striped bass. None of the prebiotics altered the culturable microbial community, but all tended to lower acetate production and increase butyrate production. A third experiment examined the effects of the four prebiotics fed to juvenile hybrid striped bass for 8 weeks. Growth, feed efficiency ratio (FER) and protein efficiency ratio (PER) were not affected by the different prebiotics, but the GI tract?s microbial community was altered from that associated with the basal diet. The fourth experiment consisted of an 8-week feeding trial and one 6-week feeding trial in which the effects of GroBiotic?-A and FOS on growth performance and microbial community composition were compared for red drum living in independent tanks versus tanks with a shared water system. Neither the intestinal microbial community nor growth performance were significantly altered by the prebiotics in these trials; fish in independent and shared water tanks produced similar results. The final experiment examined the effects of GroBiotic?-A, FOS, MOS and GOS on nutrient and energy digestibility of sub-adult red drum fed diets containing fish meal and soybean meal. The prebiotics generally increased protein, organic matter, and energy digestibility, with the exception of FOS/inulin. Lipid digestibility was decreased by GOS, MOS and FOS. These studies are the first to establish that prebiotics can alter the GI tract microbial community of these fish and influence nutrient digestibility.