Use of prebiotics, nondigestible dietary ingredients that beneficially affect the host by selectively
stimulating the growth of and/or activating the metabolism of health-promoting bacteria in the
intestinal tract, is a novel concept in aquaculture. Two separate feeding trials were conducted to
evaluate graded levels of a commercial prebiotic GrobiotickAE, a mixture of partially autolyzed
brewers yeast, dairy ingredient components and dried fermentation products, in the diet of hybrid
striped bass, as compared to partially autolyzed brewers yeast (BrewtechR). The basal diet in both
trials was formulated to contain 40% protein, 10% lipid and an estimated digestible energy level of
3.5 kcal/g. Two levels (1% and 2% of diet) of GrobiotickAE and brewers yeast were added to the
basal diet with menhaden fish meal and menhaden oil adjusted to provide isonitrogenous and
isolipidic diets. Each diet was fed to five (trial 1) or three (trial 2) replicate groups of juvenile hybrid
striped bass in 110-l aquaria twice daily at rates approximating apparent satiation for 7 weeks (trial 1)
or 4 weeks (trial 2).
Enhanced growth performance was generally observed in fish fed the diets supplemented with
GrobiotickAE or brewers yeast compared to the basal diet after 7 weeks of feeding in trial 1.
Significantly higher (P< 0.05) feed efficiency was observed in fish fed diets supplemented with 1%
and 2% GrobiotickAE. After 4 weeks of feeding in trial 2, growth and feed efficiency were not
significantly affected by the various dietary treatments, although some immunological responses
were altered. Neutrophil oxidative radical anion production and intracellular superoxide anion