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International Journal of Aquaculture 2012, Vol.2, No.7, 40
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47
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44
et al (2012) also confirmed that growth performance
of
Oreochromis niloticus
is affected by strain
variation. The authors reported that Abassa line
showed a superior final body weight at harvest (28%)
over the Kafer El Sheikh strain.
The SGR (2.59% to 2.73% /day) obtained in this study
were comparable with the report of Middendorp (1995)
for juvenile
Oreochromis niloticus
in pond culture
ranging from 2.2% to 3.1% /day. Moreover, the
specific growth rate observed in these study was
higher than the specific growth rate that reported by
Ashagrie et al (2008) (0.787% to 1.035% /day),
Abdel-Tawwab (2004) (0.967% to 1.277% /day) and
Al-Hafedh (1999) (0.49% to 0.75% /day) obtained for
juvenile
Oreochromis niloticus
. Generally, the SGR of
Koka strain was nearly 13.28%, 9.2% and 5.41%
higher than that of the Ziway, the Hora and the
Hawassa strains, respectively.
The Koka strain had the highest growth performance
with slightly lower feed conversion ratio value than
the other strains. This result is in agreement with the
work of Abdel-Tawwab (2004) who reported that the
lowest feed conversion ratio is obtained in the Aswan
strain that had the highest growth performance. The
feed conversion ratio that ranges from 1.72 to 1.76
obtained in this study was consistence with the range
of 1.45 to 2.40 for juvenile
Oreochromis niloticus
,
reported by Yi (1998) in cage culture. However, the
present result was much less than the feed conversion
ratio (3.15 to 4.86) reported by Al-Hafedh (1999). In
contrast, it was slightly higher than the feed
conversion ratio that ranges from 1.01 to 1.6 reported
by Diana et al (2004) in pond culture. Thus, it is
possible to say that different strains have different
feed conversion ratio at different environmental
conditions.
The results of the present study also showed that fish
survival for all stations was reasonably good ranging
from 96% to 100%. This result is in line with the work
of Ridha (2006) who observed that the survival rate of
juvenile
Oreochromis niloticus
was relatively high for
all strains (97.4% to 100%) in tank culture. El-Sayed
(2002) also observed that the survival rate of
Oreochromis niloticus
fry was between 90% and
100%.
The results of this study also revealed that gross fish
yield was affected by strain differences. The
maximum gross fish yield was obtained from the
Koka strain (160.09 g/m
3
) followed by the Hawassa
strain (149.08 g/m
3
). The lowest gross fish yield was
obtained from the Ziway strain (131.04 g/m
3
). The
Koka strain had 22.17% higher gross fish yield than
that of the Ziway strain. This result is in agreement
with the work of Ridha (2006) who found that the
strain with the highest growth performance had the
highest gross fish yield (45.4 kg/m
3
) and the lowest
feed conversion ratio (1.27) and the poorest growth
performance had the lowest gross fish yield (30.4 kg/m
3
)
and the highest feed conversion ratio (1.55).
In this study, length-weight relationship of all the
juvenile
Oreochromis niloticus
strains showed a
strong relationship (r
≥
88% for all strains). This
implies that the body length and body weight of the
fish was proportional and has good body condition.
Fulton’s conditional factor (1.58 to 1.82) obtained in
this study was comparable with the average value of
1.46 in Lake Ziway and 1.86 in Lake Chamo reported
by Admassu & Ahlgren (Admassu and Ahlgren, 2000).
Except Ziway strain, the growth exponent ‘b’ of
length-weight relationship obtained in this study was
nearly 3 that indicates an isomeric growth pattern.
This means that the fish shape is consistent. The
Ziway strain (3.78), however, had allotropic growth
pattern (Costa and Araújo, 2003; Olurin and
Aderibigbe, 2006).
Generally, the growth performance of the Koka strain
was ranked first followed by the Hawassa strain. The
Ziway strain had the lowest growth performance. The
results of this study clearly indicated that the Ziway
strain had the poorest growth performance among the
four strains tested, which is supported by the work of
Admassu and Ahlgren (2000) who reported that the
growth performance of juvenile
Oreochromis niloticus
strain in Lake Ziway showed the lowest growth
performance than found in Lake Chamo and Lake
Langano in their natural habitat using otolith analysis.
4 Conclusions and Recommendations
The results of the study clearly demonstrated that the
growth performance of different
Oreochromis
niloticus
strains collected from Ethiopian freshwater
lakes was significantly different in which the Koka