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beneficial consequences on reproductive performance of broodstock animals and larval quality,
as previously reported with other feed supplements (Paibulkichakul
et al.
2008).
11.4.2.2 Consideration with large scale experiments
It is interesting that very few published studies have been carried out in commercial farms or
under pond conditions. It is obvious that the efficiency of probiotics at a commercial scale will
require
in situ
validation, ideally in ponds, to highlight their true value for the farmers. People
who have worked on the evaluation of probiotics in ponds know that such work is complex
because it has to take into account numerous factors, often highly variable (different pond sizes
and configurations, zootechnical practices, date and density of seeding, origin and quality of
post larvae etc.). To compare treatments and to determine precisely whether a probiotic has an
effect or not, it is thus essential to standardize these variables as much as possible for every
pond and ideally to have numerous replicates in order to reach an acceptable statistical power
(Chim
etal.
2009). For instance, in their study, Devaraja
etal.
(2002) used three replicate ponds
of 0.5 ha in order to evaluate two commercial bioremediation products, but they did not show
significant differences among the treatments in the average production at the end of the culture
period, even though one treatment seemed to give better results. The authors finally advised the
use of larger sample sizes for further studies to show the potential benefits of using microbial
products in commercial aquaculture farms. Indeed, too small a sample size very often leads to
difficulties of interpretation, misleading results and inevitably to erroneous conclusions. It is
frequent for a farmer to observe large differences in the final survival rate between ponds of
the same farm, while no specific treatments were applied. Chim
et al.
(2009) illustrated, for
semi-intensive conditions, the within-farm variability among the ponds, and confirmed that
the specific characteristics of each pond from the same farm make it difficult to use them as
experimental units. These authors proposed the use of floating cages in shrimp culture ponds as
an economical, powerful and sensitive experimental tool for shrimp culture studies. Rengpipat
et al.
(2003) and Castex
et al.
(2008) used such experimental designs to assess respectively
the effect of
Bacillus
S11 and
Ped. acidilactici
dietary supplementation on
P. monodon
and
L. stylirostris
, respectively. The latter used a sample size of five replicate cages per treatment,
repeated in two ponds, and after 3 months there was a significant improvement in survival and
FCR, with a statistical power close to 80%.
11.5 CONCLUSION
Probiotics are applied in order to develop and fortify gut microbial communities to promote
and sustain the health of the host. The current literature provides a foundation and shows that it
is possible to achieve this goal in crustaceans. However, our knowledge of the mechanisms by
which probiotics operate in crustaceans requires a great deal of further attention, with a distinct
emphasis on the effect of probiotics on the gut microbiota. Moreover, further investigations
on the microbial communities in the digestive tract of crustaceans together with a demon-
stration of their relevance in terms of nutritional contribution and physiological implication
(notably immunity) are of utmost importance. The impact of the different rearing techniques
of crustaceans on the intestinal microbiota, especially with the development of closed recircu-
lating systems based on microbial floc, must also be investigated. A better understanding of
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