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westernkingprawn(
Penaeus latisulcatus
) (Hai and Fotedar 2009) fed MOS through formu-
lated feeds. MOS provided to larval European lobster (
Homarus gammarus
), via
Artemia
,
improved growth and survival in a dose-dependent manner. Inclusion of MOS at levels of 0.072
and 0.72 g l
-1
of
Artemia
culture water increased survival and growth compared to the control
larvae, though higher concentrations resulted in decreased survival and growth (Daniels
et al.
2006). Later studies on larval European lobster also showed significant improvements in SGR,
feed conversion and survival with MOS supplementation at 12 mg l
-1
of
Artemia
culture water
(Daniels
et al.
2010).
MOS is a glucomannan-protein complex derived from mannans and presents
mannose-binding sites (Newman 1994; Miguel
et al.
2002; Fritts and Waldroup 2003).
Attachment and colonization of bacteria on the epithelial cells of the intestine are mediated
by specific lectins on the bacterial cell surface (Newman 1994). A number of important
intestinal Gram-negative pathogens often present mannan-specific fimbriae that will bind to
the mannan receptors on MOS which is therefore hypothesized to reduce pathogen adhesion
to intestinal epithelial cells (Spring
et al.
2000; Ferket
et al.
2002: Pryor
et al.
2003). As well
as preventing pathogen attachment, MOS has also been shown to actively displace pathogens
from epithelial cells on the mucosal surface (Newman 1994). The dietary application of
MOS is well documented to provide beneficial changes in GI microbial populations in finfish
(Dimitroglou
et al.
2011;
Chapter 14
) though little work is documented on GI microbial
changes in shellfish. A recent study on the dietary supplementation of MOS in European
lobster showed stabilized bacterial communities and a reduction in total heterotrophic
bacterial counts (Daniels
et al.
2010). The results of this study also demonstrated that MOS
improved GI structure by enhancing GI absorptive surface area and increasing the uniformity,
length and density of microvilli (Figure 15.1). This effect on GI morphology and modulation
of the bacterial community may improve digestive funtion and nutrient absorption, thus
leading to improved feed conversion and growth as observed elsewhere (Genc
et al.
2007;
Hai and Fotedar 2009). Furthermore, Sang
et al.
(2011b) observed enhanced amylase and
protease activities in the mid gut and hepatopancreas of MOS fed freshwater crayfish which
may also contribute towards improved nutritional utilization and growth.
Enhanced innate immunity has been achieved by dietary application of MOS in shell-
fish species; for example, enhanced immune response was observed in Pacific white shrimp
(
Litopenaeusvannamei
) with the administration of dietary MOS at 2 and 4 g kg
-1
(Fisher
etal.
2001). Chotikachinda
et al.
(2008) also reported enhanced immune status, as demonstrated by
increased total haemocyte counts (THC) and granular haemocyte counts in the blood of
L.van-
namei
with the dietary inclusion of inactive yeast cell wall (a source of MOS and β-glucans)
at 1 and 2 g kg
-1
. A more recent study by Sang
et al.
(2009) on freshwater crayfish (
Cherax
tenuimanus
) also reported enhanced immunity, as measured by THC, differential haemocyte
counts (DHC), haemolymph clotting time and reduced haemolymph
Vibrio
load after
Vibrio
mimicus
challenge, with the dietary addition of MOS at 2 g kg
−1
and 4 g kg
−1
of the diet. This
study also showed improved immune capability measured by THC and haemolymph clotting
time in the presence of environmental stressors (such as exposure to NH
3
and air) and bacterial
infections. Similar enhancements in immunological parameters (specifically THC) have also
been observed in juvenile
P. monodon
fed MOS supplemented diets (Sang
et al.
2014).
These studies demonstrate the potential for the applications of MOS to improve crustacean
immune status, gut microbiota and gut morphology, increasing nutrient uptake and feed con-
version, improving growth and enhancing survival.
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