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International Journal of Aquaculture 2012, Vol.2, No.7, 40
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Table 3 Estimated parameters of length-weight relationship for different
Oreochromis niloticus
strains
Parameters of length-weight relationship
Types of strains
‘a’
‘b’
‘r’
Remark
Hawassa
-1.83
3.04
88.0a
Ziway
-2.66
3.78*
89.5a
Hora
-2.49
3.63
90.5a
Koka
-1.75
2.99
93.5a
3: is growth exponent (b) value that
shows isometric growth
Note: * indicate that b for Ziway strain revealed significantly (p < 0.05) different from 3, mean values in the same column having
same letter are not significantly different
Figure 5 Changes in live body weight (g/fish) of different
strains of
Oreochromis niloticus
at different sampling periods
3 Discussions
The growth performance of
Oreochromis niloticus
depends on genetic materials, food quality, energy
content of the food, stocking density and
environmental factors (Gjedrem, 1997; El-Sayed,
1999; Ashagrie et al., 2008). In this study growth
performance of different juvenile
Oreochromis
niloticus
strains collected from different Ethiopian
freshwater lakes were compared under pond culture
condition. At all experimental ponds, the different
water quality parameters (such as DO, pH, TDS and
temperature) measured during the study period were
similar and remained in the favourable range for
rearing
Oreochromis niloticus
fingerlings (Yi, 1998;
Lei and Li, 2000; Xu et al., 2005; Azaza et al., 2008).
However, the temperature was much less than that of
the temperature ranges from 28
℃
to 30
℃
which are
optimum for maximum growth of
Oreochromis
niloticus
(Beamish, 1970; El-Sayed, 2006). Moreover,
the initial mean body size of the fish was
homogeneous. Thus, variation in growth performance
and food conversion ratio of the fish for all the strains
were not affected by external factors and initial body
size among the strains. In other hand, variation in
growth performance was caused by strain variation.
Thus, in this study comparison of growth performance
of different juvenile
Oreochromis niloticus
strains
were made based on different growth parameters
including mean body weight gain, specific growth rate
and daily growth rate as indicator of growth, food
conversion ratio as indicator of feed utilization
efficiency, gross fish yield as indicator of production
potential and length-weight relationships as indicator
of growth condition and growth pattern of the fish.
The results of the present study revealed that the
growth performance of juvenile
Oreochromis niloticus
affected by strain variation and were significantly
different (p < 0.05). The Koka strain had the highest
growth performance while the Ziway strain had the
lowest growth performance. The body weight of the
Koka strain was nearly 20.53%, 14.71% and 7.4%
higher than that of the Ziway, the Hora and the
Hawassa strains, respectively. These results were in
line with the work of Abdel-Tawwab (2004), who
worked on the growth performance of four different
Oreochromis niloticus
strains collected from four
Egyptian lakes (Abbassan, Asswan, Manzalah and
Maryut lakes). The author reported that growth
performance is affected by strain differences. Ridha
(2006) made a similar observation and reported that
growth performance of
Oreochromis niloticus
is
affected by strain differences. The present result is
also in agreement with the finding of Eknath et al
(1993) and Palada-de-Vera and Eknath (1993) who
compared the growth performance of four African and
four Asian
Oreochromis niloticus
strains at different
environmental conditions. The authors found that the
growth performance of the fish was significantly
affected by strain variation in which the African
strains had better growth performance than the Asian
strains with the exception of Ghanaian strain. Ibrahim