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International Journal of Aquaculture, 2014, Vol.4, No.25 1
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7
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5
The green algae constituted an important group among
the phytoplankton in the treatment ponds. Graham and
Wilcox (2000) stated that green algae seemed to be
favored by high level of nutrients, their structural and
physiological adaptations such as small size, deformed
shapes, and formation of mucilaginous colonies which
reduce loss due to sedimentation and/or grazing by
zooplankton. The genus
Pandorina
was dominant among
the Chlorophytes in pond 2 while the genus
Euglena
was
high in ponds 2 & 3. This observation is in conformity
with those of Silva (1998) and Pereira et al
.
(2001).
Cyanobacteria have been reported to dominate in some
maturation and stabilization ponds during high
temperature periods (Pereira et al., 2001). In the present
study the genus
Oscillatoria
was found in the oxidation
ponds 2 and 3. Athayde et al
.
(2000) stated that the
micro-algae are an important part of wastewater treatment
as suppliers of oxygen in the water to augment the rate of
biochemical oxidation of the organic matter. In the
present study the occurrence of many species of
phytoplankton indicates the existence of aerobic
conditions which is essential for the fish culture.
2.4 Benthic fauna
A number of organisms were collected from the bottom
sediment and on the delicate branches of the roots of
the
Eichhornia
plant. These macro-organisms include
mainly aquatic and terrestrial insects, their larval stages,
oligochaetes and nematodes (Table 4). The nematode,
Rhabditis
sp. was recorded from the first pond only.
The
Tubifex
sp. was more common and abundant in
pond 1 and 2. The larvae of
Chironomus
and
mosquitoes were found to be higher in pond 2. The
Hemipteran bugs were found densely in ponds 1 and 3.
The snipe fly larvae was more common in pond 2. In
the oxidation pond 1, the larva of caddis fly and dragon
fly were more in numbers when compared to other
ponds. The abundance of species in oxidation ponds
might be due to their high level of tolerance to organic
pollution and low oxygen tension in the water (Moyo,
1997). The larvae of
Chironomus
and
Tubifex
were
more on the root tips than the other invertebrate
species. According to Wallace and Merritt (1980)
some species of benthos were found in high number
when algal productivity was maximum. The present
findings are in conformity with the studies of Olive and
Dambach (1973), Brightman and Fox (1976) and
Kondratieff et al. (1984) that benthic invertebrates
were concentrated in areas in the streams and wetlands
receiving organic waste. Dehghani et al
.
(2007) also
observed that sewage maturation ponds are
appropriate for the growth and development of aquatic
insects especially species of Diptera and Hemiptera.
Table 4 Benthic faunal assemblage in oxidation ponds
Species
Pond 1 Pond 2 Pond 3
Nematoda
Rhabditis
sp.
+
-
-
Oligochaeta
Tubifex
spp.
++
++++
-
Insecta
Chironomus Larvae
+
++++
Athericidae,
Atherix
-
Snipe
Flies
+
++
-
Dragonfly nymph
++
+
+
Caddisfly larva
+++
-
++
Hemiptera:Heteropteran spp.
Bug
++++
++
++++
Mosquito larvae
+
++++
++++
2.5 Total bacterial population
The population density of bacteria in the water of the
sewage pond cultured on various media are presented
in Table 5. The highest population was noticed in water
samples cultured with Pseudomonas agar in the ponds.
The highest mean density was 79 x10
3
, 74x10
3
and
107x10
3
respectively in ponds 1, 2 and 3. In the
McConkey agar medium the bacterial counts were low
and the mean value being 27 x10
3
, 29 x10
3
and 6 x10
3
in
ponds 1, 2 and 3 respectively. In the nutrient agar the
bacterial colonies were moderate in number and the mean
values were 22 x10
3
, 37 x10
3
and 17x10
3
in pond 1, 2 and
3 respectively. There was a decline in the bacterial
population in pond 3. The present results are in
conformity with the results of Rajasekaran (2008). The
results indicated the presence of
E.coli, Enterobacter
sp.
and Pseudomonas
sp. in the ponds. According to
Mara et al. (1992) the reduction in pathogens and faecal
coli forms in oxidation ponds are influenced by algal
activity or exposure to ultravio
.
Table 5 Bacterial number (CFU/ml) in oxidation ponds
Media
Pond 1(x10
-3
)
Pond 2(x10
-3
)
Pond 3 (x10
-3
)
Day1
Day2
Mean
Day1
Day2
Mean
Day1
Day2
Mean
McConkey agar
20
34
27
17
41
29
5
7
6
Pseudomonas agar
91
67
79
85
63
74
119
95
107
Nutrient agar
27
16
22
21
12
17
31
42
37