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standalone strains. The authors report some levels of protection of the probiotic-fed prawns
when challenged with
V. harveyi
, even if no data were provided. They finally reported that
when supplemented to western king prawn diet (at 2 × 10
6
CFU g
-1
) over 84 days of cul-
ture, the combination of these two strains led to improved growth, survival and FCR - this
last benefit being partially associated with changes in the morphology of the intestine. Bal-
cázar
et al.
(2007) compared the efficacy of different probiotic species to limit the mortality
of
L. vannemei
following immersion challenge with
V. parahaemolyticus
. Interestingly the
study demonstrated a similar level of protection with Gram-positive and Gram-negative bac-
teria compared with the control group, and recommended
V. alginolyticus
UTM102 and
Ps.
aestumarina
SLV22 as promising dietary probiotics to prevent vibriosis in shrimps. Pai
et al.
(2010) recently showed that two strains of
Pseudomonas
sp. (MCCB 102 and MCCB 103)
were also able to improve disease resistance of
P. monodon
larvae through active antagonism
toward
Vibrio
spp. and a particular
V. harveyi
strain. Interestingly they also selected two other
probiotic species from different genera (
Bacillus
and
Arthrobacter
) able to provide similar
benefits to the larvae but with a non-antagonistic supporting mode of action.
Other authors have recently reported alternative approaches to using
Vibrio
sp. in shrimp
diets (Krupesha Sharma
etal.
2010). These authors assessed
Vibrio
cells as potential immunos-
timulants for
P. monodon
by testing the effect of heat inactivated
V. alginolyticus
cells and
heat inactivated
V. alginolyticus
biofilm. The use of
V. alginolyticus
biofilm cells added to the
feed at a dose of 10
9
CFU g
-1
of shrimp per day for 14 days resulted in an immunostim-
ulation and an effective enhancement of
P. monodon
resistance to
V. alginolyticus
infection
and WSSV. Despite these encouraging results, the use of
Vibrio
spp. (or other autochthonous
Gram-negative bacteria) isolated locally remains controversial today since some strains have
been described to be pathogenic for crustaceans, as is the case for
V. alginolyticus
(Lightner
1993). Clearly safety concerns must be considered in the use of taxa considered pathogenic
for aquatic animals before allowing wider applications. Indeed, bacteria that are harmless for
some species might acquire virulence or be pathogenic for other species (Irianto and Austin
2002). Adapted regulations on feed additives must then be set up locally in order to control
these applications.
11.2.5 Yeast
Although various inactive yeast fractions (MOS, β-1,3 glucans, or yeast extract fractions) have
received some attention as feed ingredients for marine and freshwater shrimp species (Sahoo
et al.
2008; Ringø
et al.
2010; Smith
et al.
2003) as well as other crustaceans (Daniels
et al.
2010; Sang
et al.
2010) and are today widely used in formulated aquafeeds, the use of live
yeasts as probiotics has received little attention in crustacea.
One of the first preliminary reports on the use of live yeast and fungi in crustaceans is the
study of Intriago
etal.
(1998) which reported that a red pigmented yeast and a chitin-degrading
fungus were able to improve the growth performance of
L. vannamei
larvae. A more detailed
report from Scholz
et al.
(1999) compared different yeasts (a baker's yeast
S. cerevisiae
,a
Saccharomyces exiguus
and
Phaffia rhodozyma
) to improve performance of juvenile
L. van-
namei
over a 7 week tank culture experiment. Their results revealed that even though no clear
immunostimulatory effect was observed for the parameters assessed, all three yeasts, and espe-
cially the
Phaffia,
, had a positive effect on the animals, leading for instance to a better survival.
However, the probiotic dosage used in this study was not clearly reported and would merit fur-
ther attention to evaluate the feasibility of such application. In a more recent study, Immanuel
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