Abstract Although low levels of dietary mannanoligosaccharide (MOS) supplementation have been shown to increase weight gain, decrease feed conversion, and stimulate intestinal villi growth in domestic mammals and birds, the responses of aquacultural species to MOS have not been studied. We examined the effects of MOS supplementation on the growth of and digestive tract morphology in Gulf sturgeon Acipenser oxyrinchus desotoi. There were no differences in growth performance (as measured by condition factors, specific growth rates for weight and fork length, and feed conversion ratios), gross gastrointestinal morphology (gut length and spiral valve length), or spiral valve villi structure (villus length, width, and density) between fish fed control and MOS-supplemented diets. However, in light of the promising results obtained by similar studies across a wide range of animals, dietary MOS supplementation in other aquacultural species merits further investigation.