International Journal of Aquaculture, 2018, Vol.8, No.9, 65-72
68
In the present study the daily growth rate (0.4 g/day) attained by
O. niloticus
from Lake Chamo is close to the one
reported for
O. niloticus
by Liti and his colleagues a growth rate of 5 g/day (Liti et al., 2006). Lower daily growth
rate (0.16-0.23 g/day) is also reported by Ogunji et al. (2008). In the present study low pond water temperature
(16.8-24°C) which was not in the optimum rage for tilapia (25-32°C) and the feed quality particularly digestibility
and palatability which were not addressed in the present study could be the major reasons for the lower growth
performance of
O. niloticus
.
Figure 1 Growth curves of
O. niloticus
for the experimental ponds
The Specific Growth Rates of
O. niloticus
populations (0.8-1.1% per day) are comparable with the reports of
Abdel-Tawwab (2004) that ranged between 0.97-1.23% per day and Ashagrie et al. (2008) from 0.79-1.03% per
day. But it was lower compared to the previous reports for
O. niloticus
from other lakes in Ethiopia, 2.59-2.73%
per day (Workagegn and Gjoen, 2012). The result on Food conversion ratio that ranged between 2.5 and 4.2 in the
present study is higher than the recommended value of 1.5 for aquaculture (Stickney, 1979). Such variation might
probably be due to genetic variation, different culture environment and feed quality as it has been reported by
Guimaraes et al. (2008). It could also be the digestibility of the feed given since there is no information on the
digestibility of the locally formulated feed.
The gross fish yield per hectare per year of Lake Chamo
O. niloticus
was 1.3 and 1.7 times greater than to that of
Lake Hashengie and Lake Tana, respectively. Compared to the results from other study conducted in Kenya by
Liti et al. (2006) that ranged between 4909-5867 kg ha
-1
yr
-1
is far less than the result in the current study
(198.6-3433 kg/ha/yr) but is similar with the result of another study in Kenya (1579-2328 kg/ha/yr) which was
conducted in fertilized ponds supplemented by either maize, wheat or rice bran (Liti et al., 2005). However, our
result is twice greater than the result (131-160 g/m
3
) from similar experiment at NFALRC but supplemented with
wheat bran (Workagegn and Gjoen, 2012). The reason for such low gross yield could be due to the feed quality in
terms of digestibility which was not examined in the present study. We also used mixed sex-tilapia fingerling for
the experiment because there was no sex reversed fingerling which all together contributed for the lower
performance in growth. Slow growth in females than their male counterpart as they did not feed during oral
incubation of eggs and fry is a general fact which was also visualized in this experiment while weighing the fish in
monthly bases and also in the final harvest.
Time (days)
Initial
15 30 45 60 75 90 105 120
Mean body weight (g)
10
20
30
40
50
60
70
CH
O.n
TA
O.n
HA
O.n
