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International Journal of Aquaculture 2012, Vol.2, No.7, 40
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47
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42
than the Hora and the Ziway strains, but no from the
Hawassa strains. Similarly, mean body weight gain
and specific growth rate exhibited the same trend.
Specific growth rate deceased as rearing period
increased (Figure 1). The final mean body length of
all the strains also revealed significantly (p < 0.05)
different among the strains (Table 2).
Figure 1 Mean values of specific growth rate for different
Oreochromis niloticus
strains at different sampling periods
The best mean values of feed conversion ratio (1.72)
was achieved by the Koka strain while the poorest
mean values of feed conversion ratio (1.76) was
achieved by the Hawassa strains. In addition, the mean
value of feed conversion ratio increases with time
(Figure 2). There was also a direct relationship
between Fulton condition factor and culturing period
though out the experiment (Figure 3). However,
statistical analysis revealed that mean values of feed
conversion ratio and Fulton condition factor were not
significantly different among all the strains (Table 2).
The highest gross fish yield was achieved in the Koka
strain (160.09 g/m
3
) followed by the Hawassa
(149.08 g/m
3
) and the Hora strains (139.58 g/m
3
)
while the Ziway strain had the lowest gross fish yield
(131.04 g/m
3
). Statistical analysis revealed that the
Koka strain had significantly higher gross fish yield
than the Ziway and the Hora strains, but there not than
the Hawassa strains (Table 2). Survival rate of all the
strains was very high ranging from 96% to 100%.
As indicated by Figure 4 and Figure 5, at early life
stage, change in length was greater than change in
weight. Later, change in weight was greater than change
in weight, implying that fish grow in weight than in
length at late life stage. However, there was a strong
relationship between length and weight of the fish for
all strains (Table 3). With the exception of Ziway
Figure 2 Mean values of feed conversion ratio for different
Oreochromis niloticus
strain at different sampling periods
Figure 3 Mean values of Fulton condition factor for different
Oreochromis niloticus
strains at different sampling periods
Figure 4 Changes in live body length (cm/fish) of different
strains of
Oreochromis niloticus
at different sampling periods
strain (3.37), all the strains had not significantly different
from 3. The Koka strain had slightly higher ‘r’ value
(93.5%) than the Hawassa strain (88.0%), the Ziway
(87.7%) and the Hora strains (89.12%). This means that
length and weight of the Koka strain had higher correlation
than other strains, but statistically, there was no significant
difference among strains in their ‘r’ value.