The Gut Microbiota of Fish - Aquaculture Nutrition: Gut Health, Probiotics and Prebiotics - page 78

Phylum reported in salmonids

Deinococcus-Thermus

Tenericutes

Fusobacteria

Bacteroidetes

Actinobacteria

Firmicutes

Proteobacteria

0 2 4 6

Number of reports

8 10 12

Fig. 4.2 Bacterial phyla observed in the gut microbiota of salmonids. (Source: Nayak 2010.
Reproduced with permission of John Wiley & Sons.) For colour detail see Plate 9.

Although other genera were also present, their abundance was closer to 2%. Interestingly, in
wild salmon (entirely carnivorous), the abundance of Mycoplasma was 96% of the clones
analysed. Similarly, Pond et al. (2006) described the intestinal microbiota of rainbow trout
( Oncorhynchus mykiss Walbaum) by using a cloning approach. They reported only two major
groups among 200 clones analysed, which corresponded to Clostridium and Aeromonas .
Furthermore, Kim et al. (2007) reported that Clostridium dominated the gut microbiota in
rainbow trout analysed by denaturing gradient gel electrophoresis (DGGE). The carnivorous
diet of salmon may explain in part the low number of taxa observed, since a recent study
indicated that diet influences the bacterial diversity of the digestive tract. In this report,
a more comprehensive analysis of vertebrate gut microbiota (albeit mostly mammalian)
indicates that bacterial diversity increases from carnivore to omnivore to herbivore (Ley
et al. 2008). This has recently been observed in Antarctic fish, among which the omnivorous
Notothenia coriiceps (yellowbelly rockcod or bullhead notothen) exhibits greater diversity
than the exclusively carnivorous Chaenocephalus aceratus (blackfin or Scotia Arc icefish)
(Ward et al. 2009). This may indicate that increasing herbivory in fish leads to gut microbiota
diversification, as observed in mammals.
Descriptions of microbiota from wild fish have also been reported, especially in herbivorous
fish and also in some habitats of ecological interest. Recently, the microbiota of three fish from
a coral reef was reported (Smriga et al. 2010). The studied fish corresponded to different diets
representing two trophic levels: Chlorurus sordidus (parrotfish) is a herbivore that consumes
primarily endolithic and epilithic algae; Lutjanus bohar (two-spot red snapper) is a top preda-
tor that consumes fishes and crustaceans; and Acanthurus nigricans (whitecheek surgeonfish)