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(FlaB) has been shown to interact with TLR5 expressed on Caco-2 cells and that the binding
of FlaB with TLR5 subsequently activated downstream signalling (including elevated NF-κB)
to produce the chemokine IL-8 (Lee
et al
. 2006).
10.9 CATFISHES
Globally nearly 3 million tonnes of farmed catfish is produced annually (FAO FIGIS 2013).
Pangassius
spp. (1.4 million tonnes), Amur catfish
Silurus asotus
(397,000 tonnes), channel
catfish
Ictalurus punctatus
(376,000 tonnes), yellow catfish
Tachysurus fulvidraco
(217,000
tonnes), African catfish
Clarias gariepinus
(194,000 tonnes), wels catfish/sheat fish
Silurus
glanis
(1500 tonnes), walking catish/Indian Magur
Clariasbatrachus
and silver catish
Rham-
dia quelen
are amongst the most important species. Information on the gut microbiota compo-
sitions of catfish species, and the factors which influence them, is quite limited (
Chapter 5
and
Chapter 6
). However, a review of the literature available on the channel catfish gut microbiota,
and the potential to modulate it, is provided by Burr
et al
. (2012).
The selection of probiotic candidates for, and the application of probiotics to, catfish
species is in its infancy compared to many other farmed fish, but some information is available
for channel catfish, wels catfish, African catfish, walking catfish/Indian Magur, silver catfish
and striped catfish (
Pangasianodon hypophthalmus
) (refer to Table 10.8). Some studies have
sought to characterize and assess the potential efficacy of autochthonous catfish bacterial
strains in
in vitro
tests and these studies have demonstrated the ability of some bacterial strains
to antagonize pathogens (Hamid
et al
. 2012; Ran
et al
. 2012; Zhou
et al
. 2012b).
Lc. lactis
subsp.
lactis
strains (isolated from the intestine of African catfish) were able to inhibit the
growth of
Salmonella typhimurium
and
Escherichia coli
(Hamid
et al
. 2012), and
B. subtilis
strains (isolated from the intestine of yellow catfish) and their metabolites could antagonize
and reduce the growth of
Flavobacterium columnare
,
Edwardsiella tarda
,
A. hydrophila
,
Aeromonas sobria
and
E. coli
(Zhou
et al
. 2012b). Ran
et al
. (2012) also demonstrated that
the channel catfish intestinal tract contained a number of
Bacillus
spp. which could inhibit
the growth of fish pathogens.
B
.
subtilis
,
B
.
pumilus
,
B
.
cereus
,
B. methylotrophicus
and
B
.
amyloliquifaciens
strains showed antimicrobial activity against
A
.
hydrophila
,
Edwardsiella
ictaluri
,
Ew. tarda
,
Flavobacterium columnare
,
Str. iniae
,
Yersinia ruckeri
and
Saprolegnia
ferax in vitro
.
Some of the
Bacillus
strains isolated by Ran
et al
. (2012) were also tested
in vivo
, and
in a static rearing system with daily water changes (20-30 min) some degree of protection
was afforded to juvenile channel catfish when challenged with
Edwardsiella ictaluri
in
a 45 min immersion exposure; 18 days post challenge the strains improved survivability
rates by up to 15%. Perhaps surprisingly, a clear degree of protection was also apparent
for juvenile striped catfish when challenged with a 30 min immersion exposure to
Ew.
ictaluri
; mean mortality rates 18 days post challenge were reduced from 71% in the control
(non-probiotic fed fish) to 10-57% in the
Bacillus
fed fish (Ran
et al
. 2012). Dietary
provision of
B. thuringiensis
has been reported to improve the survival rate of African catfish
IP challenged with
A. hydrophila
(Renshwary
et al
. 2011). Although mortality rates were
not presented, the effects of dietary provision of
Lb. acidophilus
on the haematological and
immunological responses and histopathology of pathogen challenged African catfish have
been investigated (Al-Dohail
et al
. 2011). Al-Dohail
et al
. (2011) reported that infected catfish
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