International Journal of Aquaculture, 2015, Vol.5, No.3 1
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1.7 Body composition analysis
For body composition analysis, 6 fish from each tank
at harvest were randomly sampled and stored at –20 C
for subsequent chemical analysis. Analysis of samples
were made as follows, dry matter after desiccation in
an oven (105 C for 24 h.), ash incineration at 550 C
for 12 h., crude protein (microkjeldahl, N x 6.25),
crude fat (ether extraction by Soxlhet method) and
crude fiber, according to the methods of AOAC,
(1995).
1.8 Statistical analysis
Data were analyzed by two-way analysis of variance
using the SAS General Linear Models procedure
(Statistical Analysis Systems 1993). Significance
between stocking density, between water exchange
rates, and their interaction were determined using
Duncan’s multiple range test (Duncan’s, 1955).
Treatments effects were considered significant at P
0.05. All percentage and ratio data were transformed
to arcsin values prior to analysis (Zar 1984).
2 Results
2.1 Water quality
Throughout the duration of the study, water quality
parameters were not significantly different (P > 0.05)
among treatments and were averaged ± SE: water
temperature, 26.6 ±0.05 C; dissolved oxygen, 4.5 ±
0.3 mg/L; pH, 7.9 ± 0.5; total ammonia, 0.3 ±
0.1mg/L; nitrate, 1.52 ± 0.3 mg/L; alkalinity, 189 ±
43mg/L. Water quality parameters were within the
acceptable range for tilapia growth.
2.2 Fish growth and production
Effects of stocking density and water exchange rate on
mono-sex Nile tilapia,
O. niloticus
initial weight (g),
final weight (g), initial length (cm/fish), and final
length (cm/fish) after 44 weeks of rearing in concrete
tanks in the present study are presented in Table 2. It
is evident from this table that, there were no
significant differences in the initial weight and length
of fish at the beginning of the experiment. At the end
of the trial average final weight and length were
affected significantly by stocking density but not
influenced by water exchange rate. The highest
average final weight and length of fish were recorded
with the lowest stocking density (50fish/m
3
) and the
lowest were recorded in the highest stocking density
(100fish/m
3
). There were no significant interaction
between stocking density and water exchange rate.
There were a correlation between stocking density and
final average weight and length of fish. When the
stocking density was increased the final average body
weight and length of fish was decreased.
Table 2 Effects of stocking density and water exchange rate on mono-sex Nile tilapia,
O. niloticus
initial body weight (g), final body
weight (g), initial body length (cm), final body length (cm) after 44 weeks of rearing in concrete tanks. Values are means
SE
Classification
Average body weight (g)
Average body length (cm)
Initial
Final
Initial
Final
Stocking density
N.S.
**
N.S.
**
50 fish/m
3
7.5
1.15
218.9
10.9
a
8.9
0.1
22.0
0.6
a
75 fish/m
3
7.5
1.15
163.5
7.9
b
8.9
0.1
20.8
0.3
b
100 fish/m
3
7.5
1.15
132.3
6.5
c
8.9
0.1
19.0
0.3
c
Water exchange
N.S.
N.S.
N.S.
N.S.
8 liter/min.
7.5
1.15
176.3
8.7
8.9
0.1
20.4
0.4
12 liter/min.
7.5
1.15
166.9
8.1
8.9
0.1
20.8
0.3
SD x WE
N.S.
N.S.
N.S.
N.S.
R
2
0.39
0.0.31
0.29
0.20
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
