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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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