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International Journal of Aquaculture, 2014, Vol.4, No.18 108
-
112
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110
2.2 Screening of enzyme-producing strains
The composition and substrate degrading ability of
bacteria isolated from the intestinal tract of farmed
Clarias
gariepinus
is shown in Table 2. The
percentage composition of enzyme-producing
bacteria are: Protease producing strains (72.2%),
lipase producing strains (61.1%), amylase producing
strains (55.6%) and cellulase producing strains
(38.9%). All the isolates possessed multienzyme
activity. An isolate (
Bacillus
sp. B
1
) showed
activity for protease, lipase, amylase and cellulase
enzymes.
Table 2 Composition and substrate degrading ability of bacteria isolated from the
intestinal tract of farmed
Clarias gariepinus
Bacterial isolates
Enzymes
Protease (72.2%)
Lipase (61.1%)
Amylase (55.6%)
Cellulase (38.9%)
Bacillus
sp
.
B
1
+
+
+
+
Bacillus
sp
.
B
2
+
+
+
-
Bacillus
sp
.
B
3
+
+
-
-
Bacillus
sp
.
B
4
-
+
+
-
Staphylococcus aureus
+
-
-
+
Staphylococcus
sp.
+
-
-
+
Vibrio
sp. V
1
-
+
+
-
Vibrio
sp. V
2
-
-
+
+
Aeromonas hydrophila
+
-
+
-
Aeromonas
sp.
+
-
+
-
Pseudomonas aeruginosa
+
+
-
-
Pseudomonas
sp.
+
+
-
-
Lactobacillus
sp.
+
+
-
-
Escherichia coli
+
+
-
-
Salmonella
sp.
+
+
-
+
Enterobacter
sp.
-
-
+
+
Micrococcus
sp.
-
+
-
+
Flavobacterium
sp.
+
-
+
-
Note: (+) indicates positive activity; (
-
) indicates negative activity; Numbers in parentheses represent the percentage composition of
enzyme-producing strains
3 Discussion
The total heterotrophic bacterial count of 3.8±0.02 x
10
8
cfu/g in the intestinal tract of farmed
Clarias
gariepinus
reveal that dense bacterial population occur
in the digestive tract of fish. This result is in
agreement with that of Shangong et al. (2010) who
reported a total viable count of 3.4 x 10
8
cfu/g in the
intestinal content of yellow catfish (
Pelteobagrus
fulvidraco
). Al-Harbi and Udin (2005) reported that
the presence of a high bacterial load in gill and
intestine of fish might be due to high metabolic
activity of fish associated with increased feeding rates
at higher temperature. They also reported that pond
water and sediment bacteria influenced the bacterial
composition of gills and intestine of tilapia.
The genera of bacteria (Table 1) isolated from the
intestine of farmed
Clarias
gariepinus
are not
uncommon to the aquatic environment and have been
isolated by other workers (Al-Harbi and Udin, 2004;
Pond et al., 2006; Hovda et al., 2007; Kim et al., 2007
and Ariole and Kalu, 2013). The bacteria ingested by
the fish along with their diet may adapt themselves to
the environment of the gastrointestinal tract and form
a symbiotic association (Ringøand Birkbeck, 1999).
Enzymatic studies indicated that the bacterial isolates
possess the ability to degrade proteins, lipids, starch
and cellulose (Table 2). Protease activity was
exhibited by a majority of the isolates (72.2%)
reflecting that the bacterial flora associated with the
intestinal tract of
Clarias
gariepinus
are capable of
digesting foods rich in proteins. Some authors have
also established that bacteria in the digestive tract of
fish demonstrated proteolytic, lipolytic, amylolytic
and cellulolytic activities (Ghosh et al., 2002; Saha et
al., 2006; Ray et al., 2010; Sumathi et al., 2011 and
Ariole and Kalu, 2013). The presence of these