Prebiotic Applications in Shellfish - Aquaculture Nutrition: Gut Health, Probiotics and Prebiotics - page 411

2002). An improved immune status can thus be inferred by an increase in the number of
circulating haemocytes/coelomocytes as well as an increase in the level (or proportion) of
granulocytes due to their phagocytic and respiratory burst functions in shellfish (De Guise
et al. 2008).
The application of dietary scFOS can enhance total haemocyte levels in Paciic white shrimp
(Li et al. 2007) and changes in haemocyte counts and/or granulocyte proportions have also
been reported with dietary MOS supplementation in C. tenuimanus (Sang et al. 2009; 2011a)
and C. destructor (Sang et al. 2011b), tropical spiny lobster (Sang and Fotedar 2010) and
western king prawn (Hai and Fotedar 2009). The increase in total haemocyte counts reported
in freshwater crayfish C. tenuimanus increased immune capability and improved the host's
defence against V. mimicus infection and abiotic stressors such as air and NH 3 exposure (Sang
et al. 2009). While no such changes at the cellular level of the immune system have been
reported with other prebiotic supplements in shellfish, alternative indicators of immune status
have also been assessed. These immune parameters include haemocyte respiratory burst activ-
ity, phenoloxidase activity, lysozyme activity, peroxidase activity, superoxide dismutase activ-
ity, nitric oxide synthase activity, serum albumin and protein levels, clotting time, haemolymph
bacterial loading and neutral red retention time (Li et al. 2007; Hai and Fotedar 2009; Li J.
etal. 2009; Li P. etal. 2009; Sang etal. 2009; 2011a; Sang and Fotedar 2010; Wang etal. 2010;
Zhang et al. 2011). For example, enhanced humoral immune defences including phenoloxi-
dase, lysozyme, nitric oxide synthase, and superoxide dismutase activities have been observed
with the dietary addition of IMO in the shrimp Penaeus japonicus (Zhang et al. 2011). It has
been suggested that prebiotic may enhance the immunity in host species by stimulating the
growth of selected bacteria such as lactic acid bacteria and Bacillus spp. at the expense of
potentially pathogenic and opportunistic species (Shan et al. 2006). Shifts in the GI micro-
bial communities may therefore affect the host immunological status as microbes possess
cell wall components, such as lipopolysaccharides, peptidoglycan and β-glucans, that have
immunomodulatory properties in shellfish (Sritunyalucksana et al. 1999; Chang et al. 2000;
Sung et al. 2000; Hai and Fotedar 2009; Xian et al. 2009; Bai et al. 2010; Chang et al. 2011).
For example, the bacterial cell wall components peptidoglycan and lipopolysaccharides have
been shown to increase phenoloxidase (PO) activity in black tiger prawn ( Penaeus monodon )
(Sritunyalucksana etal. 1999). Another major component of probiotic Gram-positive bacterial
cell walls is lipoteichoic acid (LTA) which has reported anti-inflammatory and immunostim-
ulatory effects (Thomas and Versalovic 2010).
Not all studies have reported enhanced immunity with the dietary application of prebiotics
in shellfish; for instance, Li P. et al. (2009) reported no change in total haemocyte counts,
haemolymph protein, phenoloxidase activity, haemocyte respiratory burst or bacterial
clearance from haemolymph with the dietary application of Grobiotic-A ® fed to white
shrimp. Studies have also shown varying effects on immune response dependent on the
parameters studied; for example, haemocyte respiratory burst activity was improved in
Pacific white shrimp fed scFOS, though haemocyte phenoloxidase was unaffected (Li et al.
2007). Other studies show varying degrees of efficacy dependent on the prebiotic dosage;
Sang et al. (2011a) observed positive effects of MOS on haemolymph clotting time in
marron ( C. tenuimanus ) at dietary levels of 2 and 4 g kg -1 in comparison to control fed
individuals, although this was not observed at 0.5, 1 and 8 g kg -1 .LiJ. et al. (2009) reported
positive effects of IMO in combination with Bacillus sp. on THC in L. vannamei , although
at higher concentrations of dietary IMO (in combination with Bacillus ) results similar to
those of control fed individuals were observed. Indeed, immunosuppression has previously