International Journal of Aquaculture, 2015, Vol.5, No.22 1
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7
5
Figures 3 Changes of mean body length of fish (cm) during
different periods of the present study as influenced by stocking
density
results showed that, the increasing fish density
increased the net production of fish. The total cost of
experimental fish groups as S1; S2; S3 and S4 were
90.4, 97.8, 185.1 and 275.3 Egyptian Pound/m
3
,
respectively. Net returns calculated as returns over
costs for stocking densities of 25, 50, 100 and 150
fish/m
3
groups were -24.59; 8.41; 12.11 and 22.40
LE/m
3
, respectively. The highest net returns were
obtained by high stocking densities of fish (3.020 and
4.515 kg/m
3
) compared to the lowers and medium
(0.750 and 1.505 kg/m
3
stocking densities). Meanwhile
the highest stocking density produced more fish net
production which has a very high sell price which
reflected positively on the net returns.
Discussion
Fish stocking density is one of the most important
factor affecting fish growth and health in many ways
(Garr et al., 2011 and Zhu et al., 2011). Growth
performance and survival rate are often adversely
affected by high stocking densities (Pouey et al., 2011
and Sorphea et al., 2010) but in some experiments
Table3 Economic information for Nile tilapia reared in cages for 196 days at four stocking densities
Stocking density (kg/m
3
)
0.750 (S1)
1.505 (S2)
3.020 (S3)
4.515 (S4)
No. fish stoked
25
50
100
150
No. fish harvested
25
50
100
150
Harvest (kg per cage)
4.37
1.6
d
8.17
2.1
c
15.17
4.1
b
22.09
6.3
a
Food used (kg/m
3
)
6.52
12.13
22.52
33.38
Fingerling cost (0.5 E.Pound / fish)
12.5
25.0
50.0
75.0
Food cost (6.0 E. Pound / kg)
39.1
72.8
135.1
200.3
Total cost (Egyptian Pound/m
3
)
90.4
97.8
185.1
275.3
Value of harvest (13 E. Pound/kg)
65.81
106.21
197.21
297.7
Net profit (Egyptian Pound/m
3
)
-24.59
8.41
12.11
22.40
conditions this effect is either temporary (Garr et al.,
2011) or truant (Southworth et al
.,
2009). The findings
of this experiment indicated that, growth was inversely
related to rearing density. Also results in table 3 are in
agreement with the findings of Abdel-Hakim and
Ammar (2005) who reported that lower stocking
densities (14 or 16 thousand fish/Feddan) resulted in
significantly higher final weights and lengths of fish
compared with the 18 thousand fish/feddan densities.
Also, Ridha (2006) reported that a density of 200
fish/m
3
significantly decreased the growth performance
of Nile tilapia compared with a density of 125 fish/m
3
.
In general these results indicate that the maximum
yield occurred at the highest density (150 fish/ m
3
) but
at the expense of individual mean weight.
The same trend of a decrease with high densities of
tilapia was observed for fish length. These results are
in accordance with those of Hafez (1991), who
showed that body length of fish decreases with
increasing stocking density. Also Abdel (Hakim et al.,
1995) showed that body length of Nile tilapia stocked
at rates of 3000, 4500 and 6000 fish/Feddan after 16
weeks of treatments were 6.49; 6.29 and 5.71 cm for
males while for females body length records were
5.40, 5.18 and 5.12 cm, respectively. Some species
can resist extreme crowding although competition for
food will then limit their growth performance and lead
to inferior weight gain (Stickney, 1994). The pervious
reasons may be explained the case in this study where
fish stocked at higher stocking densities had poor
