International Journal of Aquaculture, 2015, Vol.5, No.3 1
-
13
7
Stocking Density (fish /m
3
)
Figure 3 The relation between total production and stocking
density of Nile tilapia reared in concrete tanks at either 8L/min.
or 12L/min. water exchange rates
Figure 4 The relation between final mean weight (g / fish) and
stocking density of Nile tilapia reared in concrete tanks at
either 8L/min. or 12 L/min. water exchange rates
Table 5 Effects of stocking density and water exchange rate on mono-sex Nile tilapia,
O. niloticus
total production and net production
(kg/m
3
) after 44 weeks of rearing in concrete tanks. Values are means
SE
Classification
Total fish production (kg/m
3
)
Net fish production (kg/m
3
)
Stocking density
**
**
50 fish/m
3
10.97
0.55
b
10.57
0.55
b
75 fish/m
3
12.27
0.59
ab
11.71
0.59
ab
100 fish/m
3
13.23
0.65
a
12.53
0.65
a
Water exchange
N.S.
N.S.
8 liter/min.
12.47
0.49
11.92
0.49
12 liter/min.
11.84
0.49
11.28
0.49
SD x WE
N.S.
N.S.
R
2
0.07
0.05
Note: 1. Significant level: N.S. = 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
while total production increased with increasing
stocking density (Figure 4). Stocking density showed
significant (P
0.01) effect on net production and
total production, while there was no significant effect
of water exchange rates and interaction (Table 5).
2.3 Feed utilization
Effects of stocking density and water exchange rates
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 are presented in
Table 6. From this table the results of feed conversion
ratio, feed efficiency ratio, protein efficiency ratio and
total feed intake were significantly (P
0.01) affected
by stocking density. But not affected significantly by
water exchange rates. The best results of FCR, FER
and PER were obtained at the lowest stocking density
50 fish/m
3
. There were no significant differences
between fish stocked at 50/m
3
and 75/m
3
in terms of
FCR, FER and PER. The lowest feed intake (g/fish)
was obtained at the highest stocking density of 100
fish/m
3
and there were no significant differences
between it and fish stocked at 75 fish/m
3
. The highest
food intake was achieved at lowest stocking density of
50 fish/m
3
. There was a significant interaction
between stocking density and water exchange rates in
terms of all feed utilization parameters except feed
intake.
2.4 Body composition
The effects of stocking density and water exchange
rates on mono-sex male Nile tilapia,
O. niloticus
whole fish body proximate composition (%) of Moisture,
crude protein, crude fat and crude ash after 44 weeks
of rearing in concrete tanks are presented in Table 7. it
