International Journal of Aquaculture, 2018, Vol.8, No.9, 65-72
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for the development of the sector in the country. Nile tilapia one of the favorite fish species used for aquaculture
practices in Ethiopia has different growth performances in the natural system. Gashaw and Zenebe (2008)
compiled research results on length at first maturity of
O. niloticus
from Ethiopia lakes and found out that it
ranges from 19.4 to 42 cm total length for males and 18.1 to 42 cm total length for females. Thus, the objective of
this paper was to evaluate the growth performances for
O. niloticus
from geographically isolated lakes in pond
system at the National Fishery and Aquatic Life Research Center (NFALRC).
1 Results and Discussion
1.1 Physico-chemical parameters
Physico-chemical parameters measured during the study period are presented on Table 1. The minimum and
maximum temperatures of the experimental units during the beginning of the experiment in November/December
were 16.8°C in the morning and 20.4°C in late afternoon. However, there was an increasing trend in the water
temperature after December where the minimum and maximum were 20.4°C and 24°C. On the other hand,
dissolved oxygen concentration (DO) ranged between 5.1 mg/L (at 9:00 am) and 14.7 mg/L (at one measurement)
in late afternoon (5:30 pm) which is expected as the water temperature increases the photosynthetic activity in the
water also increases.
Table 1 Temporal physico-chemical values (mean±SD) of experimental ponds
Ponds
Time of
Parameters
Measurement (hr)
Temp (°C)
DO (mg/L)
pH
Cond (Scm
-1
)
Pond 1
9:00
18.3±0.8
8.8±1.3
7.2±0.2
193.3±10
4:00
20.7±1.1
11±1.41
7.3±0.3
206.5±8.9
5:30
21.8±1.1
12.3±1.7
7.5±0.5
214.6±8.9
Pond 2
9:00
17.9±0.9
8.8±1.2
7.2±0.3
178.7±12.4
4:00
20.7±1.2
10.6±1.4
7.4±0.4
220.2±8.5
5:30
21.9±0.9
11.7±1.5
7.7±0.4
197.4±13.9
Pond 3
9:00
18.3±0.7
7.7±2.3
7.2±0.4
187±7.5
4:00
20.5±1.2
10±2.5
7.4±0.4
198.1±7
5:30
22.1±1.1
11.3±2.1
7.6±0.5
224.8±6.6
Water temperature is key for the metabolic activity and physiological functions of aquatic animals (e.g. feed
utilization, feed conversion, growth rates) (Halver and Hardy, 2002; Azaza et al., 2008; Workagegn and Gjoen,
2012; Zenebe et al., 2012). Temperature has indirect effect on the survival and growth of fish. The temperature
effect could be also one of the factors for the generally low performance of
O. niloticus
populations in the current
experiment compared to the results of similar studies. The DO concentration was relatively higher compared to
similar studies (Liti et al., 2005; Workagegn and Gjoen, 2012). This could be due to algal growth which had low
grazing pressure from fish as they mainly fed on formulated feeds. Relative abundance of phytoplankton species
(Table 2) also contributed for the elevated DO concentration in ponds.
Table 2 Phytoplankton species identified during the study period (1-4 indicates frequency of occurrence where 1 = rare, 2 = sporadic,
3 = common and 4 = abundant)
Species
Relative abundance
Species
Relative abundance
Pediastrum
sp.
4
Nitzschia
sp.
1
Haematococcus
sp.
3
Anabaena
sp.
3
Zygnema
sp.
3
Synedra
sp.
1
Staurastrum
sp.
1
Microcystis
sp.
1
Coelastrum
sp.
1
Oocystis
sp.
1
Scenedesmus
sp.
3
Peridinium
sp.
1
Cymbella
sp.
1
Euglena
sp.
4
Navicula
sp.
1
Phacus
sp.
2
