Factors Affecting Beta-Glucan prevention of bacterial diseases in fish

Authors: Welker, Thomas

Submitted to: Annual Meeting World Aquaculture Society
Publication Type: Abstract Only
Publication Acceptance Date: 3/5/2011
Publication Date: 3/12/2011
Citation: Welker, T.L. 2011. Factors Affecting Beta-Glucan prevention of bacterial diseases in fish. Annual Meeting World Aquaculture Society. 11:38.

Interpretive Summary:

Technical Abstract: Glucans, particularly ß-1,3-glucan, added to fish feeds have shown promise in not only stimulating immune function but also in increasing disease resistance, but the results are highly variable with no clear trends discernable, even within many fish species. Several factors, including fish size, age, and species, bacterial pathogen, and water quality, contribute to this variability. However, glucan exposure dose, which is dictated by dietary concentration and feeding duration, may be the most important factor influencing the effectiveness of dietary ß-glucan supplementation on bacterial diseases in fish. Elevated levels of glucan intake, either through high dietary concentrations, extended feeding (normally, >4 weeks), or both, are thought to overload glucan receptors on phagocytic cells. Decreased immunity through elevated dietary intake of glucan has been reported in a number of fish species. Several studies have suggested that feeding of an unsupplemented basal diet for 1 to 2 weeks should follow administration of ß-glucan diets for optimal effects on immune function enhancement and disease resistance in fish, but research doesn’t always back this claim. Furthermore, current disease challenge models may not be adequate for assessing the effects of dietary glucans on immunity. The method of challenge (immersion vs. ip injection), challenge concentration of the bacterial pathogen, and the absence of stress may not represent culture conditions that lead to disease in intensive aquaculture. These factors further confuse dietary use of glucans and require further investigation. The optimal ratio of feeding duration and dietary ß-glucan concentration may be species and pathogen specific and additionally influenced by the factors mentioned, making determination of an effective feeding regimen difficult. Factors affecting glucan efficacy will be examined with examples from research and the literature.