The Gut Microbiota of Fish - Aquaculture Nutrition: Gut Health, Probiotics and Prebiotics - page 81

(A)

Bacterial genus-Gram negative
Shewanella spp.

Moraxella spp.

Acinetobacter spp.

Achromobacter spp.

Flavobacterium spp. Marine water

Freshwater

Aeromonas spp.

Vibrio spp.

Pseudomonas spp.

0 5 10

Number of fishes

15 20

(B)

Bacterial genus-Gram positive

Lactococcus sp.

Comobacterium spp.
Actinomyces spp.

Lactobacillus spp.
Staphylococcus spp.

Marine water
Freshwater

Streptococcus spp.

Micrococcus spp.

Corynebacteriaceae spp.

Bacillus spp.

0 5 10

Number of fishes

15 20

Fig. 4.3 Aerobic Gram-negative (A) and Gram-positive (B) bacterial species reported in the GI tract of
marine and freshwater fish. (Source: Data from Izvekova 2007.)

Gram-positives (B) as they have been observed in the GI tract of marine or freshwater fish. It is
interesting that some bacterial genera such as Vibrio , Pseudomonas , Bacillus and Micrococcus
spp. are more frequently observed. It is also observed that some bacteria showed a tendency
or preference for a particular environment (marine or freshwater). The anaerobic microbes
reported in the gut microbiota of fish are graphically represented in Figure 4.4; Clostridium
and Bacteroides seem to be the most frequent anaerobic bacterial genera in fish intestines.
A graphical representation of the phyla observed in different fish is shown in Figure 4.5.
This figure indicates that the predominant microbiota present belong to five phyla: Proteobac-
teria, Firmicutes, Actinobacteria, Bacteroidetes and Fusobacteria. These different phyla