International Journal of Aquaculture, 2015, Vol.5, No.3 1
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Table 6 Effects of stocking density and water exchange rate on mono-sex Nile tilapia,
O. niloticus
feed conversion ratio (FCR), feed
efficiency ratio (FER), protein efficiency ratio (PER) and feed intake (g/fish) after 44 weeks of rearing in concrete tanks. Values are
means
SE
Classification
FCR
FER
PER
Feed intake (g/fish)
Stocking density
**
**
**
**
50 fish/m
3
2.33
0.05
a
0.44
0.01
a
1.29
0.02
a
492.0
29.3
a
75 fish/m
3
2.46
0.06
a
0.42
0.01
a
1.23
0.04
a
388.3
22.8
b
100 fish/m
3
2.67
0.04
b
0.38
0.01
b
1.12
0.02
b
333.7
18.1
b
Water exchange
N.S.
N.S.
N.S.
N.S.
8 liter/min.
2.46
0.04
0.42
0.01
1.23
0.03
410.3
20.2
12 liter/min.
2.51
0.04
0.40
0.01
1.20
0.02
397.0
22.2
SD x WE
**
**
**
N.S.
R
2
0.20
0.17
0.0.17
0.17
Note: 1. Significant level: N.S. = P
0.05, * = P
0.05, ** = P
0.01. 2. Means that have the same superscript letters within each
classification column are not significantly different from each other. 3. SD = Stocking density; WE = water exchange
Table 7 Effects of stocking density and water exchange rates on mono-sex male Nile tilapia,
O. niloticus
whole fish body composition
(%) of moisture, crude protein, crude fat and crude ash after 44 weeks of rearing in concrete tanks. Values are means
SE
Classification
Moisture
Crude protein
Crude fat
Crude ash
Stocking density
N.S.
*
*
**
50 fish/m
3
71.4
0.33
53.7
0.39
ab
22.8
0.88
b
18.2
0.32
a
75 fish/m
3
71.9
0.38
54.3
0.47
a
23.4
0.45
ab
16.4
0.59
b
100 fish/m
3
71.7
0.65
52.7
0.30
b
24.9
0.46
a
17.7
0.52
ab
Water exchange
N.S.
N.S.
N.S.
N.S.
8 liter/min.
71.7
0.43
53.2
0.35
23.4
0.66
17.4
0.56
12 liter/min.
71.6
0.34
53.9
0.34
24.0
0.40
17.5
0.24
SD x WE
**
N.S.
**
**
R
2
0.20
0.17
0.0.17
0.17
Note: 1. Significant level: N.S. = P
0.05, * = P
0.05, ** = P
0.01. 2. Means that have the same superscript letters within each
classification column are not significantly different from each other. 3. SD = Stocking density; WE = water exchange
is evdent from this table that, whole body moisture
content did not significantly (P ≥ 0.05) influenced by
either stocking density or water exchange rate. Whole
body protein, fat and ash contents were not influenced
by water exchange rate, but these means were
significantly (P ≤ 0.05) influenced by stocking density.
The highest whole body protein content was recorded
with fish stocked at 75 fish/m
3
, but the lowest was at
50 fish/m
3
.The lowest whole body fat was achieved
with fish stocked at 50 fish/m
3
, but the highest was at
stocking density of 100 fish/m
3
. The highest whole
body ash was resulted with fish stocked at 50fish/m
3
,
but the lowest was at stocking density of 75 fish/m
3
.
2.5 Economic information
The Economic information for mono sex Nile tilapia
reared in concrete tanks for 44 weeks at three stocking
density at two water exchange rates are presented in
Table 8. From this table the net profits were directly
related to stocking density and water exchange rates.
The fingerling cost (Lever Egyptian) increase by
increasing stocking density. Also, the food cost and
total cost (Lever Egyptian) increases by increasing
stocking density. From the economic information it
can be concluded that the highest net profit (Lever
Egyptian) was achieved at stocking density of 75 fish /m
3
at 8 L/min. water exchange rate in concrete tanks.
3 Discussion
There are several factors supporting the use of
intensive fish culture in recalculating systems.
Increasing land costs and decreasing freshwater
supplies are the main reason for intensification of fish
farming in Egypt, though additional advantages
include savings in manpower and easier stock
management. Increased fish yields in conventional,
static ponds or reservoirs was accomplished by a
combination of management procedures, the most
