International Journal of Aquaculture, 2016, Vol.6, No.3, 1
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9
4
2.3 Multiple Antibiotic Resistance (MAR) indexing
The MAR indexing of the isolates was determined by calculating the ratio between the number of antibiotics to
which an isolate is resistant and the total number of antibiotics to which the isolate was exposed (CLSI, 2007).
3 Results and Discussion
3.1 Enumeration and Characterisation of Gut associated bacteria
Total viable count (TVC) of heterotrophic bacteria ranged between 0.2 x 10
4
to 0.65 x 10
7
cfu/ml and 1.7 x10
6
to
6.8 x10
6
cfu/mlin the gut of
Aplocheilus lineatus
and
Etroplus maculatus
respectively. A total of fifty six isolates
(26 from the gut of
A. lineatus
and 30 from the gut of
E. maculatus
) were selected for characterisation and further
analysis. Characterisation of the isolates revealed that
Lactobacillus
sp. is the predominant genus in the gut of
A.
lineatus
followed by genera such as
Bacillus, Micrococcus
.
Aeromonas
sp.
Micrococcus
sp. was found to be the
dominant genera in the gut of
E. maculatus
followed by genera
Bacillus
,
Lactobacillus
, and
Vibrio
(Figure 3).In
both these fishes the gut associated bacterial flora was found to be dominated by Gram positive forms. Results are
in agreement with the microbiota that has been reported previously from the guts of different species of fishes
(Ray et al., 2012). Predominance of
Corynebacterium
sp. and
Bacillus
sp. in the gut of freshwater ornamental
fishes such as
Puntius filamentosus
and
Barilius bakeri
respectively, have been reported (Nashad et al., 2015).
However, Sakata (1990) reported that freshwater fish species tend to be dominated by members of the genera
Aeromonas
,
Plesiomonas
, members of the family Eneterobacteriaceae, and obligate anaerobic bacteria of the
genera
Bacteroides, Fusobacterium
, and
Eubacterium
.
Aeromonas veronii
has been isolated from the ascitic fluid
of
Astronotus ocellatus
(Oscar) showing signs of infectious dropsy in India (Sreedharan et al., 2012). Hathaet al.
(2005) reported
A. hydrophila
to be the predominant species followed by fish
A. caviae
and
A. sobria
in the gut of
cultured freshwater fishes
.
However, the aerobic heterotrophic bacteria in the gut of these fishes were found to be
dominated by Gram positive forms. These variations are accounted due to factors like bacterial host specificity,
food type, and water resource (Verner et al., 2003).
Figure 3 Distribution of various genera of heterotrophic of bacteria in the gut of a)
A. lineatus
b)
E. maculatus
The fishes selected in the study are indigenous to the back water systems of Cochin estuary, which has undergone
considerable organic pollution during the last decade. The number of people living along the waterfront has
increased dramatically and domestic waste often finds their way to these water bodies.
Bacillus
is often found to
be a dominant genera of heterotrophic bacteria associated with waters that are organically rich as the copious
extracellular hydrolytic enzymes produced by them help utilize these nutrients much more effectively than the
other ones.
E. maculatus
and
A. lineatus
found thriving in these waters and in close association with the bacterial
flora of these waters. It is proven fact that gut microflora of the fish is considerably influenced by that of the water
and food where it lives. Dominance of
Bacillus
in the gut of these fishes might be a reflection of such as
association.
