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S. cerevisiae
(Essa
et al
. 2010). Other potential mechanisms include improved microbiota
composition or activity and may potentially include elevated intestinal endocytic activity or
improved intestinal morphology as reported with probiotic applications in other fish species
(Sáenz de Rodrigáñez
et al
. 2009; Merrifield
et al
. 2010b; Pirarat
et al
. 2011).
On the other hand, a number of studies have reported no difference in tilapia growth perfor-
mance with probiotic applications (Shelby
et al
. 2006; Ferguson
et al
. 2010; Liu
et al
. 2013;
Standen
et al
. 2013) or even decreased growth (Abd El-Rhman
et al
. 2009). These studies
highlight the importance of selecting the appropriate probiont and optimum dosage. It should
be noted that growth performance in line with that of the control group, that is, no improve-
ments in growth performance, should be viewed positively if other benefits such as elevated
immune responses and disease resistance are achieved.
10.6.2 Effects of probiotics on tilapia immunity and
disease resistance
An investigation of the efficacy of live and dead probiotic cells, supplemented via the feed or
rearing water, revealed that the oral administration of live cells seemed to be most effective
at stimulating the non-specific immune responses of Nile tilapia (Taoka
et al
. 2006). Subse-
quently, most research therefore on probiotics has been conducted with the supplementation
of live probiotics to feed. The effects of probiotics on the immune response of tilapia are quite
comprehensive. Most studies have focused on the innate response, owing to its greater role
in fish as opposed to homeotherms, and the effect at both the systemic and the localized (i.e.
intestinal) levels have been observed.
At the systemic level it has been commonly reported that various probiotics can improve
tilapia serum or plasma lysozyme activity (Taoka
et al
. 2006; Aly
et al
. 2008b; Wang
et al
.
2008b; Ferguson
et al.
2010; Zhou
et al
. 2010a; 2010b; Ridha and Azad 2012), serum comple-
ment activity/concentration (Wang
et al
. 2008b; Pirarat
et al
. 2006; 2011), serum bactericidal
activity (Taoka
et al
. 2006; Abdel-Tawwab
et al
. 2008; Aly
et al
. 2008b; Pirarat
et al
. 2011)
and serum total Ig levels (Ridha and Azad 2012); elevate peripheral leukocyte levels (Aly
etal
.
2008c; Ferguson
et al.
2010); modulate the proportions or abundance of peripheral leukocyte
subpopulations (Aly
etal
. 2008c; Standen
etal
. 2013); enhance HK chemiluminescence activ-
ity (Pirarat
et al
. 2011) and respiratory burst activity (Taoka
et al
. 2006; Aly
et al
. 2008b;
2008c; Wang
et al
. 2008b; Zhou
et al
. 2010a; 2010b); and modulate immunoregulatory gene
expression profiles in immunologically relevant organs (e.g. kidney and spleen) (Pirarat
et al
.
2011; Villamil
etal
. 2012; Liu
etal
. 2013). In addition, in some studies haematological profiles
and serum or plasma biochemistry parameters have also been affected by probiotic treatment
(Taoka
et al
. 2006; Wang
et al
. 2008b; Abdel-Tawwab
et al
. 2008; Aly
et al
. 2008b; Abd
El-Rhman
et al
. 2009; Salem 2010; Abdel-Tawwab
et al
. 2010; Ferguson
et al.
2010; Zhou
et al
. 2010a; 2010b; Jatoba
et al
. 2011; Ridha and Azad 2012; Abumourad
et al
. 2013).
At the localized level, the supplementation of
Lb. rhamnosus
GG (at 10
10
CFU g
-1
) has
been reported to promote tilapia intestinal structure and mucosal immunity (Pirarat
etal
. 2011).
Tilapia fed the probiotic for 30 days displayed greater villous height in all parts of the intestine
and, significantly, in the proximal and distal regions. The number of intraepithelial leuko-
cytes (IELs) and the abundance of a subpopulation of acidic granulocytes was significantly
higher in the proximal intestine of the probiotic group than in the control group. In addition,
the abundance of goblet cells was significantly higher in the distal intestine. In addition, the
same probiotic (
Lb. rhamnosus
GG) and same dose was applied by Ngamkala
et al
. (2010)
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