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Aquaculture 231 (2004) 445 – 456 www.elsevier.com/locate/aqua-online

Dietary brewers yeast and the prebiotic GrobiotickAE influence growth performance, immune responses and resistance of hybrid striped bass (Morone chrysops  M. saxatilis) to Streptococcus iniae infection
Peng Li, Delbert M. Gatlin III *
Department of Wildlife and Fisheries Sciences and Faculty of Nutrition, Texas A&MUniversity System, College Station, TX 77843-2258, USA Received 18 July 2003; received in revised form 25 August 2003; accepted 26 August 2003

Abstract 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 anestimated 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 approximatingapparent 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 intrial 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

* Corresponding author. Tel.: +1-979-847-9333; fax: +1-979-845-4096. E-mail address: d-gatlin@tamu.edu (D.M. Gatlin). 0044-8486/$ - see front matter D 2004 ElsevierB.V. All rights reserved. doi:10.1016/j.aquaculture.2003.08.021

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P. Li, D.M. Gatlin III / Aquaculture 231 (2004) 445–456

production of head kidney macrophages tended to be higher in fish fed diets supplemented with brewers yeast or GrobiotickAE, while extracellular superoxide anion production of head kidney macrophages from fish fed diets with 1% and 2% brewers yeast and 1%GrobiotickAE was significantly ( P < 0.01) higher than that of fish fed the basal diet. All groups of fish fed brewers yeast and GrobiotickAE showed a significantly ( P < 0.01) enhanced survival (73.3 – 90%) after bath exposure to Streptococcus iniae compared to fish fed the basal diet (53.3%). Based on these data, it is concluded that GrobiotickAE and a partially autolyzed brewers yeast can serve asfunctional feedstuffs in the diets of hybrid striped bass by enhancing growth performance and immunological responses. Further research is needed into the mechanism(s) of action for prebiotics such as GrobiotickAE and their application in aquaculture. D 2004 Elsevier B.V. All rights reserved.
Keywords: Prebiotics; Hybrid striped bass; GrobiotickAE; Brewers yeast; Saccharomyces cerevisiae; Immuneresponse; Bacterial resistance; Streptococcus iniae

1. Introduction Hybrid striped bass production is considered to be the fastest growing segment of the US aquaculture industry over the past decade and has spread to several countries and regions in Europe and Asia (Harrell and Webster, 1997; Hiney et al., 2002). It is known that most of the common disease-causing organisms associated with various...
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