The effect of stress caused by environmental pollution and farming conditions on the health and yield of fish in intensive aquacultures is becoming increasingly important.

1. May | June 2012
Feature title: Brewers’ yeast as a
supplement in aquaculture
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2. FEATURE
Brewers’ yeast
as a supplement in aquaculture
by Jan Frericks, Leiber GmbH, Germany
T
he effect of stress caused by envi- therapeutic antibiotics for fish. The transfer of nutrients accumulate within the cells of the
ronmental pollution and farming genes for resistance between different spe- yeast species Saccharomyces cerevisiae. Being
conditions on the health and yield cies of bacteria is accelerated, leading to an organically bound ensures high availability
of fish in intensive aquacultures is exacerbation of the problem of resistance in of these active substances. Dried brewers’
becoming increasingly important. the treatment of human diseases worldwide. yeast is used very often in fish nutrition due
Future-oriented production methods in to the high bioavailability of the constituent
Factors such as stocking density, con- the fish farming industry should therefore compounds.
tamination, toxins, pollutants and outbreaks of be targeted towards minimising the use of In addition to this, brewers’ yeast has
disease have a negative effect on the immune antibiotics and medicinal drugs. It is of great cell walls that are composed of mannan-
status of the fish. The consequence of this is importance to analyse the negative effects oligosaccharides (MOS). This complex net-
an increased susceptibility to infection through caused by environmental pollution and farm- work of mannans and ßglucans serves as a
bacterial, viral, fungal or parasitic pathogens. ing methods. substrate for the beneficial gut flora. The
Increased loss rates and reduced growth More crucial still will be to influence the fish's limited digestive tract benefits in
performance result in lower profitability for animal's metabolism so that external toxins particular from the prebiotic properties of
the fish production industry. have a lesser impact, even under intensive the yeast cell walls, which stabilise the gut
As a consequence, the monetary and conditions. A healthy gut and a functioning and ensure a healthy balance of microflora
"The cell wall of brewers’ yeast comprises approximately 20-25%
mannans and 25-30% ß-glucans. ß1,3/1,6(D) glucan molecules can
be isolated from it using special hydrolytic processes. The molecules
consist of characteristic (1,3)-beta-glycosidic linked D-glucose
subunits connected with with irregular beta-(1,6)-linked side chains of
various length. Only this free ß-glucan structure from Saccharomyces
cerevisiae has an immunomodulatory effect on the metabolism"
quantitative overheads for the vaccination non-specific immune response are fundamen- (eubiosis). In addition to this, the mannan-
and medicinal treatment of the fish increases. tal prerequisites for this. oligosaccharides in brewers’ yeast are able
In many cases, antibiotics are given not only to bind harmful toxins in the food, and
therapeutically, but also prophylactically as a Excellent for the gut thus inhibit their absorption and resultant
standard additive in fish feed. Brewers’ yeast cells are like miniature metabolic harm. Last but not least, the for-
The intensive farming methods used for power houses, and are responsible for the mation of a biofilm on the intestinal mucosa
fish cultivation in aquatic environments with alcoholic fermentation that takes place during enhances this protective barrier against
a direct connection to the groundwater are the brewing stage of beer production. In the pathogens.
especially liable to facilitate the very rapid course of the fermentation of malt extract,
and direct spread of problematic production high concentrations of minerals and trace Glucan and the immune system
residues to humans. Resistant pathogens and elements, amino acids and nucleotides, B The cell wall of brewers’ yeast com-
germs do not just limit the effectiveness of vitamins and enzymes, as well as many micro- prises approximately 20-25 percent mannans
40 | InternatIonal AquAFeed | May-June 2012

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4. FEATURE
Tests were recently performed
on several species of fish that Oral administration tests
Purified ß1,3/1,6(D)glucans enhance the
confirm a stimulatory effect on the animals' non-specific immune response. This is
non-specific immune system of particular value in the fish farming industry,
as there are multiple stress and environmen-
tal factors that impact and stress the fish. If
they become infected, the specific immune
system is only able to respond slowly and
inadequately. In such situations, a heightened
non-specific capability can support or acceler-
ate the specific immune response and the
production of specific antibodies.
Fish are subject to similar, added stresses
during vaccinations too. A study by Siwicki
et al. (2011) investigated the effect of orally
administered ß1,3/1,6(D)glucan (100mg or
and 25-30 percent ß-glucans. ß1,3/1,6(D) ß-glucan products is not only the source and 200mg Leiber® BetaS per kg of feed) on the
glucan molecules can be isolated from it using characteristic molecular structure, but also the antibody secreting cells (ASC) and specific
special hydrolytic processes. The molecules purity of the product. A minimum content of antibody titres after immunisation of rainbow
consist of characteristic (1,3)-beta-glycosidic 70 percent pure ß1,3/1,6(D)glucan should be trout fingerlings (Oncorhynchus mykiss) by
linked D-glucose subunits connected with aimed for. The standard grade Leiber® BetaS immersion with anti-enteric redmouth disease
with irregular beta-(1,6)-linked side chains of has a ß-glucan content of 80 percent. The met- vaccine (AquaVac ERM). Inoculation was per-
various length. Only this free ß-glucan struc- abolic activity of this product has already been formed one week after the start of administra-
ture from Saccharomyces cerevisiae has an tested on many animal species and verified. tion with Leiber® BetaS.
immunomodulatory effect on the metabolism. Tests were recently performed on sev- These two parameters were measured
In contrast with intact yeast cells or man- eral species of fish that confirm a stimulatory on day seven, 14, 21, 28 and 40 in the
nan-oligosaccharides, free ß1,3/1,6(D)glucan effect on the non-specific immune system. blood serum and adrenal glands. Both dos-
molecules are able to pass through the pro- Rainbow trout and carp received 0.02 percent age levels stimulated the number of specific
tective epithelial barrier in the gut with the ßglucan (Leiber® BetaS) administered in their ASCs and specific antibody levels, whereby
help of specialised M cells. In gut-associated feed ration. The potential killing activity of 0.02 percent Leiber® BetaS in the fish
lymph tissue (GALT), ß-glucans act like anti- phagocytes, the proliferative response of T feed was more effective. In each case the
gens, stimulating specific macrophage recep- and Blymphocytes and the concentration of improvements were significant from day 21
tors with their characteristic surface structures immunoglobulins and lysozymes in the blood onwards.
(epitopes) (Engstad and Robertsen 1993). A serum was measured four weeks and eight The beneficial effect of ß1,3/1,6(D)glucan
cascade of immune responses is triggered, weeks after beginning administration. In two is well known in the fish nutrition industry. The
and non-specific immune system cells such as repetitions, a significant stimulation of these administration of 0.02 percent Leiber® BetaS
monocytes, natural killer cells, B-cells, T-cells parameters was demonstrated in both rain- in fish feed activates the non-specific immune
or lysozymes are released or activated. They bow trout and carp. status of the fish on the one hand, and on
put the animal on a high state of alert and In subsequent infection studies using two the other, acts as an adjuvant during vaccina-
preparedness to defend against all types of bacterial (Aeromonas salmonicida; Yersinia tions, thus enhancing the immunocompetence
foreign attack. What differentiates this from ruckeri) and one viral pathogen (IPN virus), of the fish. Its safe and simple method of
an actual infection is that ß-glucan does not the survival rate of rainbow trout and carp use, as well as the fact that ß-glucan from
possess any pathogenic properties, and acts with 0.02 percent Leiber® BetaS in their feed Saccharomyces cerevisiae is harmless to fish
without causing any adverse health effects. showed an absolute increase of 30-40 percent and the environment, will become yet more
A quality criterion for the effectiveness of (Siwicki, et al. 2008; Siwicki, et al. 2009). important in the future. ■
42 | InternatIonal AquAFeed | May-June 2012

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May-June 2012 | InternatIonal AquAFeed | 43

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