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etal. (2007) fed P.monodon post larvae with Artemia nauplii enriched with/without a commer-
cial probiotic preparation containing a live strain of S.cerevisiae . They showed that shrimp fed
enriched Artemia exhibited slightly higher weight gain and higher specific growth rate (SGR).
More interestingly, in the probiotic group, increased survival of post larvae subjected to V.har-
veyi infection was also observed and associated with a reduced pathogen load in the muscle
and the digestive gland. A recent study conducted in a commercial farm in Mexico assessed
the effect of a particular strain of S. cerevisiae ( S. cerevisiae var. boulardii ) fed either alive
or inactivated (at a 0.04% inclusion rate) to L. vannamei juveniles (experiment using floating
cages), and revealed that only the 'live' form was able to significantly improve survival and
feed utilization over the 60 day experiment (Lallemand unpublished results).
Patra and Mohamed (2003) were the first to report the application of the same yeast strain
( S. cerevisiae var. boulardii ) in an aquatic live feed organism. The aim of this study was to
enrich Artemia nauplii with the probiotic and then to look at resistance to a V.harveyi infection.
Indeed, Artemia nauplii, which are recognized as the best natural live feed available for larval
culture, are often used as a model organism to study host-microbe interactions, and to evaluate
probiotic bacteria before testing on target organisms (Marques et al. 2006b). In this study,
the authors reported enhanced survival of nauplii receiving the yeast compared to the control
larvae. Interestingly a dose effect could be detected with best results obtained when S.boulardii
was administered at 10 4 CFU ml -1 (90% survival rate after 48 h compared to 40% in the
control group). A study by Soltanian and colleagues (2007) considered the effects of various
yeast strains administered to gnotobiotic Artemia culture. They revealed a protective effect of
the different yeast supplements toward Vibrio pathogens; the intensity of the protection was
dependent on the yeast strain tested and was likely linked to the structure and the composition
of the yeast cell wall.
Marine yeasts have also been studied for their probiotic potential. The yeast Candida sake
was assessed for its immunostimulatory properties in F. indicus sub-adults (Sajeevan et al.
2006). The authors reported that C. sake S165 supported an optimal immune response and
increased the survival of shrimps after a WSSV challenge. However, significant improvements
were only reported with a 10% inclusion rate which is impractical at the industrial scale. More
recently, Yang et al. (2011) selected a red marine yeast ( Rhodosporidium paludigenum ) based
on its high content of carotenoids and its ability to grow in L. vannamei intestinal mucus. Sub-
sequently it was demonstrated that this yeast could enhance growth, survival and antioxidant
competence of L. vannamei when fed at 10 8 CFU g -1 of feed (fresh yeast) or at a 1% inclusion
rate (dry yeast). However, once again the high dosage levels considered can be questionable
in terms of both practical implication for feed formulations and cost. Dose-response studies
should therefore be addressed in order to further assess the efficacy of live yeast as probiotics
for crustaceans.
11.3 PROBIOTIC MODES OF ACTION
Several studies on probiotics in crustaceans have been published over the last two decades.
However, in the past the authors have mainly focused their evaluations on the benefits in terms
of survival, resistance to disease or growth performance in order to demonstrate the concept.
Even though more in-depth studies have been published over the last five years, little infor-
mation is available today on the precise mode of action of probiotics in crustaceans. Besides,
 
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