Prebiotic Applications in Shellfish - Aquaculture Nutrition: Gut Health, Probiotics and Prebiotics - page 412

been proposed in the presence of high concentrations of immunostimulatory feed additives
(Bricknell and Dalmo 2005) which may be a result of an overstimulation of the immune
system (Sakai 1999). This was hypothesized to be the case where higher concentrations of
MOS supplementation (7.2 g l -1 live feed culture water) reduced European lobster survival,
compared to the control and lower MOS concentrations (0.072 and 0.72 g l -1 ) (Daniels et al.
2006).
Despite the potential for immunosuppression at high dosage levels, the ability of prebiotics
to positively modulate the immune response has shown great potential to enhance disease
resistance in shellfish culture (Li J. et al. 2009; Sang et al. 2009; Sang and Fotedar 2010;
Zhang et al. 2011). For instance dietary application of IMO has been reported to increase
resistance against Vibrio alginolyticus in shrimp ( Penaeus japonicas ) (Zhang et al. 2011) and
against the white spot syndrome virus (WSSV) in Pacific white shrimp (Li J. et al. 2009).
Similar enhancements in disease resistance have also been demonstrated when supplementing
MOS to the diet of freshwater crayfish, as indicated by a reduction of Vibrio levels within
the haemolymph of individuals fed MOS in comparison to control fed individuals, following
V. mimicus infection (Sang et al. 2009). A later study by Sang and Fotedar (2010) also showed
enhanced disease resistance as indicated by increased survival in the tropical spiny lobster fed
with MOS at 0.4g kg -1 when challenged with Vibrio spp. This study also showed reduced
haemolymph bacteraemia and reduced THC and granular haemocyte counts associated with
enhanced survival post Vibrio challenge (Sang and Fotedar 2010). A later study also reported
reductions in bacterial concentrations within the haemolymph, similar to those recorded with
enhanced disease resistance, showed in freshwater crayfish with the dietary use of MOS (Sang
et al. 2011a). However, alternative studies supplementing Grobiotic-A ® (Li P. et al. 2009)
and MOS (Zhang et al. 2012) to the diets of L. vannamei showed no effect on the clearance
of bacteria from haemolymph, although it should be noted that both of these studies used
alternative stressors to disease.
15.3.3 GI microbiota
Despite the fact that prebiotic benefits are driven by enhanced growth or activity of beneficial
microbes, there remains a scarcity of information available on the effect of prebiotics on shell-
fish GI microecology with the use of prebiotics (Li et al. 2007; Zhou et al. 2007; Daniels et al.
2010; 2013; Sang and Fotedar 2010). Applications of MOS have been reported to increase the
stability of bacterial populations in the GI tract of larval European lobster by increasing the
similarity of microbial profiles within treatment replicates (Daniels et al. 2010). In this study
culture-dependent techniques revealed that dietary MOS did not affect Vibrio levels but did
reduce the total number of aerobic heterotrophic bacteria at certain larval stages. In tropical
spiny lobster juveniles fed MOS, however, elevated cultivable GI total aerobic bacteria and
Vibrio spp. levels have been reported (Sang and Fotedar 2010).
A study by Li et al. (2007) also assessed whole bacterial community changes in GI micro-
biota using denaturing gradient gel electrophoresis (DGGE), which showed microbial commu-
nity changes with the application of scFOS in L.vannamei . scFOS decreased the abundance of
a Roseobacter sp. and increased abundance of a number of unidentified uncultured microbes
(most similar to microbes from aquatic environments, sediments and the GI tract of mammals)
and Alkalibacillus sp. Overall, the microbial communities from the two scFOS treatments
(0.1% and 0.8% dietary inclusion) displayed 74.9% similarity to the control community; in
contrast, the communities of the two scFOS treatments were highly similar to each other