International Journal of Aquaculture, 2015, Vol.5, No.22 1
-
7
6
growth. Similar results for Nile tilapia were obtained
by Huang and Chiu (1997), El-Sayed (2002), and
(Ayyat et al
.
,
2011) who found that the increase of
stocking density had adverse influence the growth of
Nile tilapia.
The survival rate (100%) was not affected significantly
by the rearing density, suggesting that there was no
competition for space. These results agreed with
(Daungsawasdi et
al., 1986) who reported that mortality
in Nile tilapia raised in cages was not dependent on
stocking density. Tilapias are hardy and can survive
poor conditions including high stocking densities and
will continue to reproduce even at very high densities
(Delince, 1992). Moreover, the good survival rate of
Nile tilapia at high density indicates the amenability
of this fish to the intensive culture practice. The
stocking density had a significant effect (
P
<0.05) on
the estimated condition factor of experimental fish
groups. The pervious findings were accordance with
Ammar (2009) who found that averages of gain in
weight, daily gain, specific growth rate and condition
factor were influenced significantly with tilapia initial
weight and stocking density. On the other hand,
Huang and Chiu (1997) found that condition factor
and survival of Nile tilapia had not been significantly
affected by rearing density. Water quality parameters
in the cages were within the required ranges for the
growth of
Oreochromis niloticus
mono sex males
during the experiment . Water quality plays a significant
role in the biology and physiology of fish and may
impact on the health and productivity of the culture
system (Boyd, 1997). Throughout this experiment,
water quality across all the groups was within the
favorable range required for tilapia (Boyd, 1997); the
variation in fish growth in this study may not therefore
be strictly attributed to the characteristics of water
quality parameters.
The results of Table 3
suggest that stocking of Nile
Tilapia fingerlings at lower densities (25 or 50 fish/m
3
)
may have an economic advantage over higher density
(150 fish/m
3
) when fattening period is lasted to over 6
months. These results are in accordance with the
findings of Abdel- Hakim et al
.
,
1995, who reported
that total yield of Nile tilapia cultured in earthen
ponds increased with each increase in stocking density,
however averages of body weights decreased in a
parallel manner.
Diana et al., 1994 showed that, the growth curves of
fish in ponds and cages in both experiments were
more or less linear indicating that the critical standing
crop in either ponds or cages was not exceeded
possibly due to the initially low stocking density and
provision of a pelleted feed in addition to fertilization.
Conclusion
The results explained that, stoking Nile tilapia fingerlings
at 150 fish/m
3
and initial weight of 30 g/fish in cages with
protein diet at 30.2% is more preferable for two cycle’s culture
per year which get a suitable net returns.
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