International Journal of Aquaculture, 2018, Vol.8, No.9, 65-72
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1.2 Plankton species composition
A total of 17 phytoplankton species: six green algae, four diatoms, four blue greens, two euglenas and one
dinophyta were identified during the study period (Table 2). The most frequently observed algal species were
Pediastrum, Haematococcus and Euglena species which can be utilized by the fish. On the other hand,
zooplanktons were represented by 10 rotifers, 2 cladocerans and 1 copepod species. The cladocerans were smaller
sized species like
Moina
and
Diaphanosoma
which could favor for the dominance of rotifers.
1.3 Growth performances
Data on the growth performances of
O. niloticus
from the three lakes are presented in Table 3. The maximum
body weight attained by
O. niloticus
from Lake Chamo, Lake Tana and Lake Hashengie were 67.2, 42.1 and 49.9 g,
respectively. The minimum body weight (48.9 g) of
O. niloticus
for Lake Chamo was even higher than the
maximum recorded of
O. niloticus
from Lake Tana (42.1 g) but was similar to that of Lake Hashengie (49.9 g).
Table 3 Growth performances of
O. niloticus
from geographically isolated lakes in pond system at Sebeta
Parameters
Oreochromis niloticus
from lakes
CH
TA
HA
Initial mean weight (g)
16.7±1.1
a
14.9±0.6
a
16.9±1.2
a
Final mean weight (g)
59.6±9.5
a
39.4±4.5
c
46±5.3
b
Mean weight gain (g/fish)
42.9
a
±8.7
24.5
c
±3.9
29.1
b
±4.5
Mean daily growth rate (g/day)
0.4
a
±0.07
0.2
b
±0.03
0.2
b
±0.04
Specific growth rate (%/day)
1.1
a
±0.11
0.8
b
±0.07
0.8
b
±0.07
Feed conversion ratio (FCR)
2.5
a
4.2
b
4
b
Survival (%)
95
84
94
Gross fish yield (kg/ha
/
yr)
3433
1985.7
2718.5
Mean growth performance values of
O. niloticus
from Lake Chamo (final mean weight, mean weight gain per fish,
mean daily growth rate, SGR and FCR) were significantly higher (
p
<0.05) than
O. niloticus
populations from
Lake Tana and Lake Hashengie. On the other hand, no significant differences (
p
<0.05) in percent survival of
O. niloticus
were observed between Lake Chamo and Lake Hashengie. Similarly there was no significant
difference (
p
<0.05) in SGR and FCR between
O. niloticus
from Lake Tana and Lake Hashengie. Relatively lower
percent survival of
O. niloticus
was recorded from Lake Tana than from those in Lake Chamo and Lake
Hashengie (Table 3).
O. niloticus
from the three lakes showed similar growth curve trend (Figure 1). Slow linear growth in the first 60
days of culturing periods and then exponential growth after wards were observed in all the treatments. Growth
curves of
O. niloticus
from Lake Chamo separated from that of Lake Tana after 15 days of stocking and get
widened after 60 days till the final harvest. But growth curves of
O. niloticus
from Lake Chamo and Lake
Hashengie start widened after 45 days of stocking and the maximum (11.4 g) in the final harvest. The curve for
O. niloticus
from Lake Chamo demonstrated higher fish growth than
O. niloticus
from Lake Tana and Lake
Hashengie.
Higher growth rate and similar growth curve trend for
O. niloticus
from Lake Chamo compared with growth rates
of
O. niloticus
from Lakes: Ziway, Tana and Hashengie were also reported (Zelalem, 2013). Data from similar
experiment on
O. niloticus
from geographically isolated lakes: Lake Chamo, Lake Ziway, Lake Tana and Lake
Hashengie conducted between similar period with this study also revealed that
O. niloticus
from Lake Chamo
showed higher growth rate over the others (Source: Adamneh unpublished data). However, the daily growth rate
obtained in this study is much lower than the results reported for
O. niloticus
. According to Liti et al. (2005),
O. niloticus
fed with and without premix attained a daily growth rate ranging between 1.3 and 1.5 g/day.
Worekagegn and Gjoen (2012) also reported a daily growth rate ranging between 0.68 and 0.86 g/day for different
O. niloticus
strains.
