Effects of the Prebiotics GroBiotic®-A and Inulin on the Intestinal Microbiota of Red Drum, Sciaenops ocellatus

Two separate feeding trials examined the effects of dietary supplementation of the prebiotics GroBiotic((R))-A and inulin on growth performance and gastrointestinal tract microbiota of the red drum, Sciaenops ocellatus. In the first feeding trial, fish meal-based diets without prebiotics or supplemented with either GroBiotic((R))-A or inulin at 1% of dry weight were fed to triplicate groups of juvenile red drum (initial weight of 2.6 g) in 110-L aquaria operated as a brackish water (7 ppt) recirculating system for 8 wk. In the second feeding trial, soybean meal/fish meal-based diets supplemented with either GroBiotic((R))-A or inulin at 1% of dry weight were fed to triplicate groups of red drum (initial weight of 15.8 g) in 110-L aquaria operated as either a common recirculating water system or closed system with individual biofilters (independent aquaria) for 6 wk. Supplementation of the prebiotics in either feeding trial did not alter weight gain, feed efficiency ratio, or protein efficiency ratio of red drum fed the various diets. In the second feeding trial, the culture system significantly affected weight gain, feed efficiency ratio, and protein efficiency ratio although there were no effects of dietary treatments on fish performance or whole-body protein, lipid, moisture, or ash. Denaturing gradient gel electrophoresis (DGGE) analysis of the gastrointestinal tract microbial community showed no effect of the dietary prebiotics as the microbial community appeared to be dominated by a single organism with very low diversity when compared with other livestock and fish species. DGGE of the microbial community in the biofilters of the independent aquariums showed a diverse microbial community that was not affected by the dietary prebiotics.