International Journal of Aquaculture, 2013, Vol.3, No.7, 30
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31
male mono-sex tilapia (Phelps and Popma, 2000).
There is significant sex-specific difference in the growth
of fish where males usually grow faster and more
uniform in size than females (Bwanika et al., 2007).
This is mainly attributed to reproduction which
drains energy primarily for the production of eggs
and offspring’s (Eyualem and Getachew, 1992;
Tadesse, 1997). Moreover, in a mouth brooder fish
species like
O. niloticus
females fast during the early
stages and probably throughout the brooding period
which causes inconsistent feeding and subsequently
affects the body condition (Tadesse, 1988; Demeke, 1994).
Elsewhere, the culture of all-male tilapia is well
established for increased production potential and
low management requirements in semi-intensive
pond culture system, however this has not been
tasted under Ethiopian condition. This study was therefore,
conducted to compare the growth performance of male
mono-sex and mixed-sex Nile tilapia (
Oreochromis
niloticus
)
in pond culture system under Ethiopian
culture condition at Sebeta.
1
Results
The mean value of key water quality parameters of
the experimental ponds are given in Table 1. With the
exception of conductivity, other water quality parameters
measured were not significantly different (P>0.05)
among the treatments. The mean DO concentrations
were (8.76±2.03) mg/L and (9.18±1.97) mg/L
(
SD)
for mixed sex and mono-sex groups, respectively.
pH ranged between 8.00 and 9.00, whilst the specific
conductivity ranged from 190 μS/cm to 230 μS/cm
in both experimental groups.
Table 1 The mean value of some water quality parameters
recorded from the experimental ponds
Parameters
Mixed-sex
Male mono-sex
Pond area (m
2
)
200.00
200.00
Depth (m)
1.00
1.00
pH
8.40
8.50
Conductivity (µs/cm)
194.00
223.00
Mean monthly air
Temperature (
℃
)
22.00
22.00
Mean monthly water
temperature (
℃
)
18.70
18.70
Dissolved oxygen (mg/L) 8.76
9.18
Data on the growth performance, feed conversion
ratio, yield, Fulton’s condition factor and survival
rate of male and mixed-sex
Oreochromis niloticus
are presented in Table 2. Significant variations were
observed in growth performance among male and
mixed-sex
Oreochromis niloticus
reared under the
same culture condition (P<0.05, Figure 1). After 240
days the fish attained an average weight of
(176.20
±18.01) g and (108.20±15.40) g for male and
mixed-sex group, respectively. The net weight and
daily growth rate per fish were (132.65±5.30) g and
0.55
g/d for male and (68.85±3.18) g and 0.29 g/d
for mixed sex group, respectively. Mortality rate of
fish in both treatments was around 33% and showed
no significant difference (P>0.05) among the experimental
groups throughout the culture period (Table 2). The
gross and net fish production were 4 087 kg·ha
-1
·
Y
-1
and 2 384 kg·ha
-1
·
Y
-1
for all male group, whereas
2 437
kg·ha
-1
·
Y
-1
and 1 421 kg·ha
-1
·
Y
-1
for mixed-sex
group, respectively. The maximum harvest weight of
a fish in the male mono-sex (at 6
th
month) and
mixed sex (at 7
th
month) were 324 g and 197 g,
respectively.
Table 2 Comparisons of growth performance, feed conversion ratio, yield, Fulton condition factor and survival rate of mixed and
mono-sex tilapia in pond culture system (Mean ± SD)
Growth parameters
Experimental groups
Mixed-sex
Male mono-sex
Initial weight (g)
39.40
± 1.85
43.60
± 1.05
Initial length (cm)
12.90
± 1.13
13.50
± 1.13
Final weight (g)
108.20
± 15.4
176.20
± 18.01
Final length (cm)
18.80
± 0.3
22.50
± 0.63
Total weight gain (g)
68.85
± 3.18
132.65
± 5.3
Daily growth rate (g/d)
0.29
±0.02
0.55
±0.02
FCR
86.50
61.70
Fulton Condition Factor
1.58
1.63
Total net yield (kg/ha)
1421.64
2384.08
Net production (kg·ha
-1
·
Y
-1
)
2437.00
4087.00
Survival rate (%)
65.50
67.50