Probiotic Modulation of the Gut Microbiota of Fish - Aquaculture Nutrition: Gut Health, Probiotics and Prebiotics - page 187

Studies have demonstrated modulation of the fish gut microbiota after probiotic applica-
tion of both Gram positive bacteria such as Bacillus , Micrococcus and lactic acid bacteria
(LAB) (e.g. Carnobacterium , Enterococcus , Lactobacillus and Weissella ) and Gram negative
bacteria such as Aeromonas , Photorhodobacterium , Pseudomonas , Phaeobacter , Shewanella
and Vibrio . Additionally dietary supplementation of yeast, such as Saccharomyces cerevisiae ,
Debaromyces hansenii and Rhodotorula glutinis , has also been demonstrated to modulate the
indigenous gut microbiota of fish (Gatesoupe 2007). Probiotic applications may yield popula-
tions potentially resident on the epithelium, in the intestinal mucus and/or in the digesta. The
establishment of probiotic populations present in the pyloric caeca, stomach and intestine has
been reported and these probiotic populations can influence the indigenous microbiota lev-
els as well as composition. The sensitivity of the GI microbiota to probiotic modulation does
not appear to be restricted by fish maturation as several investigations have demonstrated the
effects of the probiotics on the gut microbiota of fish across a range of life stages, including
larval (via live preys), fry, fingerlings, juvenile and adult stages. The present chapter reviews
the current literature on the effect of probiotic applications on the microecology of the fish GI
tract.
8.2 BACILLUS spp.
Bacillus subtilis and Bacillus licheniformis are among the most well studied probiotic species
in fish. However, Bacillus cereus (Hidalgo et al . 2006), Bacillus circulans (Ghosh et al . 2004),
Bacillus pumilus (Aly et al . 2008; Sun et al . 2011a), Bacillus clausii (Yang et al . 2012),
Bacillus toyoi (Chang and Liu 2002; Hidalgo et al . 2006), Bacillus amyloliquefaciens (Ridha
and Azad 2012) and unidentified Bacillus spp. (Gatesoupe 1993; Del'Duca et al . 2013) have
also been investigated. Despite the numerous Bacillus probiotic applications in fish, relatively
few have included comprehensive assessments of the impact on GI microecology (refer to
Table 8.1). These studies have however demonstrated that probiotic Bacillus applications can
elevate fish GI Bacillus levels (Newaj-Fyzul etal . 2007; Bagheri etal . 2008; Ghosh etal . 2008;
Merrifield etal . 2010b; 2010c; 2010d; Sun etal . 2011a; Mohapatra etal . 2012; Del'Duca etal .
2013), modulate indigenous or total bacterial levels (Chang and Lui 2002; Bagheri et al . 2008;
Ghosh et al . 2008; Ridha and Azad 2012; Del'Duca et al . 2013) and alter indigenous bacterial
community composition (Chang and Lui 2002; Bagheri et al . 2008; Ghosh et al . 2008; Sun
et al . 2011a).
Newaj-Fyzul et al . (2007) demonstrated that high levels of B. subtilis (originally isolated
from the intestine of rainbow trout) dominated both the intestinal contents (allochthonous)
and intestinal mucus (autochthonous) of rainbow trout fed dietary levels of 10 7 CFU g -1
for a period of 14 days. B. subtilis was recovered at 5.3 × 10 4 CFU g -1 in the gut contents
and 8.1 × 10 4 CFU g -1 in the gut mucus, which equated to nearly 70% of the total cultured
populations in both the mucus and gut contents. The study demonstrated that the establishment
of B. subtilis populations in the intestinal tract stimulated cellular and humoral immune
responses (i.e. respiratory burst, serum and gut lysozyme, peroxidase, phagocytic killing, total
and α1-antiprotease and lymphocyte populations) which subsequently provided protection
against a virulent Aeromonas sp. Successful establishment of intestinal Bacillus populations
in rainbow trout was further demonstrated by Bagheri et al . (2008) and Merrifield et al .
(2010b; 2010c; 2010d) who investigated the effects of the commercial product BioPlus