Western Indian Ocean J. Mar. Sci. Vol. 12. No. 1, pp. 37-45, 2013
© 2014 WIOMSA
Survival and Growth of Tilapia zillii and Oreochromis
urolepis urolepis (Order Perciformes; Family
Cichlidae) in Seawater
Alex Nehemia1, Aviti Mmochi2 and Matern Mtolera2
1
Faculty of Science, Sokoine University of Agriculture, PO Box 3038, Morogoro, Tanzania;
2
Institute of Marine Sciences, PO Box 668, Zanzibar, Tanzania.
Keywords: Tilapia, Oreochromis, survival, growth, freshwater, seawater
Abstract—The potential for Tilapia zillii and Oreochromis urolepis urolepis
culture in seawater was evaluated by determining their survival and growth in
seawater at 35‰. Fingerlings were collected from Pangani River using seine
nets and reared in 1 m3 concrete ponds after acclimatization from salinity of
2‰ to 35‰. Fingerlings were also reared in freshwater as controls. Fingerlings
were fed twice daily using commercial fish feeds (White Rose floating pellets),
initially at a rate of 5% of their total body weight (TBW) and 10% of their TBW
after two weeks. Their growth rate (length and weight) was recorded weekly
except controls for handling, their growth being recorded at the beginning
and end of the experiment. The average weight gain (g.week-1), percentage
weights gain (week-1) and specific growth rate (SGR, %.day-1) were determined
in freshwater and seawater. There was no significance difference (p >0.05) in
the SGR between the two species in seawater. The survival rates of O. urolepis
urolepis were 100% in freshwater and seawater and 89% and 96% respectively
for T. zillii. This study showed that T. zillii and O. urolepis urolepis can survive
and grow in seawater but the former is a better candidate for mariculture.
INTRODUCTION
As >25% of its surface is submerged under
fresh and marine water, Tanzania has one of the
highest levels of natural tilapiine fish diversity
(Trewavas, 1983). Efforts to artificially rear
tilapia in Tanzania can be traced back to the
Corresponding author: AN
Email: alexander_nehemiah@yahoo.co.uk
1950s when successful experimental farming
was carried out at Korogwe (Tanga) and
Malya (Mwanza). In the mid-1950s about
1000 ha (8000-10000 ponds) were farmed,
producing about 2000 tons annually (Maar et
al., 1996). Lack of proper management, use of
inappropriate technology, drought, inadequate
38
A. Nehemia et al.
extension efforts, poor infrastructure to
facilitate marketing, as well as competing
sources of tilapia from capture fisheries in
Tanzania’s great lakes, resulted in a decline in
production. In the mid-1970s, 2000 tons were
produced per annum, which had decreased to
1,000 tons by the 1980s (Rice et al., 2006).
At present, aquaculture is largely a
subsistence activity practiced by poor
households in Tanzania. Rural people that
are far from major freshwater bodies depend
on aquaculture as a source of income,
animal protein and occasional employment.
However, since the output of capture fisheries
is decreasing (Akimbo et al., 2001) Tanzania
will depend increasingly on aquaculture for
its aquatic protein resources, not only in the
inland but more so in coastal areas, due to the
ample availability of seawater.
Some tilapias have higher survival
and growth rates in saline waters than in
freshwater. For instance, Liao and Chang
(1983) reported faster growth in Taiwanese red
tilapia, a crossbreed between mutant reddishorange female Oreochromis mossambicus
(Peters, 1852) and normal male O. niloticus
(Lovshin, (1998), in brackish and salt water
than in freshwater. Canagaratnam (1966)
demonstrated that O. mossambicus grew
better in saline water, with the highest growth
rate recorded in 50:50 sea and freshwater.
This is close to the isotonic equilibrium for
the fish and, therefore, it expends only a
little energy to maintain its osmotic balance
(Febry & Lutz, 1987). As a result, there is
a lower demand on the thyroid gland at this
salinity and faster growth. Job (1969) stated
that, as salinities approached isotonicity in O.
mossambicus (12.5‰), there was a reduction
in osmotic load and a lower osmoregulation
cost, which allowed more energy to be spent
on growth with a corresponding increase
in oxygen uptake. This corresponded to the
isotonic equilibrium between the fish and its
surrounding environment but was found to be
size dependent.
This study was thus devised to establish
whether Tilapia zillii (Linnaeus, 1758) and
Oreochromis urolepis urolepis (Norman,
1922) from Pangani River can survive and
grow in seawater, and whether their survival
and growth would differ between seawater
and freshwater.
MATERIALS and METHODS
Collection and stocking of
fingerlings
Oreochromis urolepis urolepis fingerlings
weighing 5.3-42 g (4.8-12.3 cm) and Tilapia
zillii weighing 11.9-15.4 g (7.4-11.0 cm)
were collected from the Pangani River using
seine nets and transported to the Institute of
Marine Sciences-Mariculture Center (IMSMC) at Pangani in Tanga, Tanzania. The two
species were identified according to Eccles
(1992) and Pullin (1988). Fingerlings were
acclimated for the experimental procedures
by adding seawater to their holding tanks in
daily increments of 2% to 35%.
Pond design and experimental set up
Twelve 1.0 m3 concrete ponds were randomly
stocked with ten fingerlings of both O. urolepis
urolepis and T. zillii, of about the same weight
for the growth experiments at the IMS-MC. The
experiment was undertaken in two replicates
with two controls, the first at zero salinity
(freshwater) in which the fingerlings were
weighed weekly. The second comprised preweighed, seawater-acclimated fingerlings left
undisturbed without reweighing until the end
of the experiment. This was done to evaluate
the effect of handling on fingerling survival
and growth. The treatment ponds were stocked
with seawater-acclimated fingerlings and
weighed weekly to the end of the experiment.
Assessing fingerling survival and
growth
Growth rates were measured by recording
total body length using a measuring board and
body weight using a digital balance (Cen-Tech
model no: 95364) reading to 0.01 g. Survival
was monitored at regular intervals by counting
the number of surviving fingerlings. All dead
Survival and Growth of Tilapia zillii and Oreochromis urolepis urolepis in Seawater
fish found in the ponds were removed using a
scoop net and recorded. Growth performance
was determined in terms of average weight
gain, percentage weight gain and specific
growth rate (SGR):
Average weight gain (g) = [Σ (final weight –
initial weight)] ÷ N fingerlings
% weight gain.fish-1 = [(final weight – initial
weight) ÷ initial weight] x 100
Specific growth rate (%.day-1) = [(ln final
weight – ln initial weight) ÷ no of days] x100
Feeding
Fingerlings were fed manually using commercial
feed (White Rose floating pellets) twice every
day (morning and afternoon) at a designated end
of the pond. The pellets contained a minimum
of 20% protein and 4% fat, and a maximum
of 5, 12 and 10% fibres, ash and moisture
respectively. The fingerlings were initially fed
5% of their total body weight (TBW) weekly
and 10% of their TBW weekly thereafter.
Data analysis
Data analysis was conducted using Microsoft
Excel, ver., 2007 and Origin pro 7 software.
Results were presented as means with standard
deviations. The statistical significance of
differences between measured parameters
was calculated using one-tailed T-tests at a P
level of <0.05.
39
RESULTS and DISCUSSION
Growth rate of Tilapia zillii in
seawater
The specific growth rates (SGR), average
and percentage weight gain of Tilapia zillii in
seawater are presented in Tables 1 and 2 and
Figure 1. Yidirim et al. (2009) found that T.
zillii attained a daily SGR ranging from 2.122.98%.day-1 in brackish water with a salinity
of 11% when fed with feeds with crude protein
ranging from 16.57-18.49%.day-1. El-Sayed
(1989) recorded an SGR of 0.54-0.87%.day-1
for this species, while Abdel-Tawwab (2008)
recorded an SGR of 0.10-0.82%.day-1. The
SGR values obtained in this study (Table
5) ranged from 0.9%.day-1 in the handling
control ponds to 1.13%.day-1 in the treatment
ponds and are close to those obtained by
Abdel-Tawwab (2008) and El-Sayed (1989)
but lower than those of Yidirim et al. (2009).
They indicate that T. zillii can grow as well in
seawater as in brackish water.
Growth rate of Tilapia zillii in
freshwater
The specific growth rates, percentage weight
gain and the average weight gain of the
freshwater T. zillii control fingerlings are
presented in Table 1 and Figure 2. Polat
(1998) found T. zillii had an SGR ranging
from 2.26-3.04%.day-1 in freshwater and
Table 1. Mean weekly weight of Tilapia zillii in the seawater treatment and freshwater control ponds (± SD).
Growth parameters
Number
of weeks
Mean weight
(g)
Mean weight in
following week (g)
Seawater
Freshwater
control
Seawater
1
15.4±2.2
7.10±1.6
2
19.1±4.9
9.0± 6.3
3
20.0±2.3
4
5
Mean weight gain
(g.fish-1)
Freshwater
control
Seawater
Freshwater
control
19.1±4.9
9.0± 6.3
3.7±1.3
1.9±2.6
20.0±2.3
10.4±1.4
0.9±0.1
1.38± 0.5
10.4±1.4
22.3±3.3
11.9±2.0
2.3±1.8
1.48±1.9
22.3±3.3
11.9±2.0
22.4±1.8
12.3±2.2
0.1±0.1
0.4±0.3
22.4±1.8
12.3±2.2
24.9±2.1
12.9±3.1
2.5±0.7
0.5±0.5
6
24.9±2.1
12.9±3.1
27.7±2.5
14.6±3.0
2.8±1.1
1.8
7
27.7±2.5
14.6±3.0
28.3±2.5
14.8±3.3
0.6
0.2
8
28.3±2.5
14.8±3.3
28.9±2.2
15.2±3.3
0.6±0.3
0.4±0.3
40
A. Nehemia et al.
35
30
% Weight gain
25
20
15
10
5
0
0
1
2
3
4
5
6
7
8
Weeks
% Weight gain
Figure 1. Percentage weight gain of Tilapia zillii in seawater.
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
0
1
2
3
4
5
Weeks
Figure 2. Percentage weight gain of Tilapia zillii in freshwater.
6
7
8
9
9
Survival and Growth of Tilapia zillii and Oreochromis urolepis urolepis in Seawater
Table 2. Growth rate of Tilapia zillii in seawater of
35% (handling control) (± SD).
Growth parameters
Value
Mean weight day 1 (g.fish )
15.9 ±2.5
-1
Mean weight after 8 weeks (g.fish-1)
26.4±5.7
Mean weight gain after 8 weeks (g.fish ) 10.5 ±7.4
-1
Percentage weight gain (%)
66.0±8.3
the values recorded by Rana et al. (1996)
ranged from 6.1-7.65%.day-1, while Jegede
and Olusola (2010) recorded a range of
0.72-1.17%.day-1. The mean value of 1.37%.
day-1 obtained in this study (Table 5) was
close to the range obtained by Jegede and
Olusola (2010) but less than the findings of
Rana et al. (1996) and Polat (1998). These
differences may be attributable to different
experimental conditions.
Growth rate of Oreochromis
urolepis urolepis in seawater
The growth rates attained by Oreochromis
urolepis urolepis in seawater are presented
in Tables 3 and 4 and Figure 3. The growth
performance of Florida red tilapia (FRT;
Oreochromis mossambicus x Oreochromis
niloticus) has been assessed in brackish and
seawater. Watanabe et al. (1989) established
that its SGR was 3.34%.day-1 when reared
41
in cages at salinities ranging from 34-41‰
and 3.46%.day-1 in seawater pools of 37‰
salinity; the value obtained by Paz (2004) for
its SGR in brackish water was 3.9%.day-1.
The SGR results for O. urolepis urolepis in
seawater in this study (Table 5) were 0.71%.
day-1 in the treatment ponds and 1.2%.day1
in the handling control ponds, poor values
when compared to the cited studies. This
may be due to better growth performance by
the hybrid cross. O. urolepis urolepis also
manifested negative growth during the first
week of acclimatization to saline conditions,
probably due to delayed adaptation to the new
environment and food.
Growth rate of Oreochromis
urolepis urolepis in freshwater
The growth of O. urolepis urolepis in
freshwater is presented in Figure 4. Lamtane
et al. (2008) found that its SGR of in fresh
water was 1%.day-1 while Paz (2004) reported
an SGR of 3.9%.day-1. We obtained an SGR
for O. urolepis urolepis of 2.9%.day-1 in
freshwater; differences from the cited works
may be attributable to differences in stocking
density and environmental conditions. Again
this species showed negative growth rate
in one of the replicate during the first week
in freshwater, indicating that it took time to
adapt to the new environment and food.
Table 3. Mean weekly weight of Oreochromis urolepis urolepis in the seawater treatment and freshwater
control ponds (± SD).
Growth parameters
Number
of weeks
Mean weight
(g)
Mean weight in
following week (g)
Seawater
Freshwater
control
Seawater
1
34.5±6.2
2.92±0.2
2
33.8 ±5.9
2.7±0.3
3
37.3±6.2
4
5
6
45.3±6.8
9.4±3.7
7
46.9±4.6
11.2±2.1
8
49.2±3.9
13.3±1.4
51.3±4.6
Mean weight gain
(g.fish-1)
Freshwater
control
Seawater
Freshwater
control
33.8±5.9
2.7±0.3
-0.7±1.3
-0.22
37.3±6.2
3.9±0.5
3.5±2.7
1.9±0.1
3.89±0.5
42.0±7.3
5.3
4.7±2.1
1.5±1.5
42.0±7.3
5.3
44.3±6.5
6.5
2.3±2.1
1.2±0.4
44.3±6.5
6.5
45.3±6.8
9.4±3.7
1.0 ±0.9
2.9±0.6
46.9±4.6
11.2±2.1
1.6±0.8
1.8±0.6
49.2±4.6
13.3±1.4
2.1±0.7
2.1±0.1
14.7±1.5
2.1±0.7
1.4±0.9
42
A. Nehemia et al.
15
% Weight gain
10
5
0
0
1
2
3
4
5
6
7
8
9
10
11
Weeks
-5
-10
Figure 3. Percentage weight gain of Orechromis urolepis urolepis in seawater.
Comparison of growth between
Tilapia zillii and Oreochromis
urolepis urolepis
The growth rate of T. zillii in the treatment
ponds in terms of its percentage weight gain
and SGR was higher (Table 5, Figure 5)
than that of O. urolepis urolepis. The latter
responded poorly to seawater in the first week
and T. zillii was more tolerant and adapted
Table 4. Growth rate of Oreochromis urolepis urolepis
in seawater of 35% handling control) (± SD).
Growth parameters
Value
earlier to its new environment and food
than O. urolepis urolepis; this may be due to
genetic differences in their adaptation to saline
conditions. However, the differences between
the growth of T. zillii and O. urolepis urolepis
in seawater were not significant (P >0.05) but,
in freshwater, O. urolepis urolepis manifested
significantly higher growth (P =0.005).
Table 5. Mean specific growth rates (± SD) of
Tilapia zillii and Oreochromis urolepis urolepis
over eight weeks.
Specific
growth rates
Mean weight on day 1 (g.fish-1)
12.5±2.1
Mean weight after 56 days (g.fish-1)
24.2±2.8
T. zillii in 35% seawater (treatment)
1.13%
Mean weight gain (g.fish )
11.7±1.0
T. zillii in freshwater (control)
1.37%
Weight gain (%)
93.6±9.9
-1
T. zillii in seawater (handling control)
0.9%
O. urolepis urolepis in seawater
(treatment)
0.71%
O. urolepis urolepis in freshwater
2.9%
O. urolepis urolepis in seawater
(handling control)
1.2%
%Weight gain
Survival and Growth of Tilapia zillii and Oreochromis urolepis urolepis in Seawater
90
80
70
60
50
40
30
20
10
0
-10 0
-20
-30
-40
-50
-60
-70
1
2
3
4
5
6
7
43
8
9
Weeks
Figure 4. Percentage weight gain of Oreochromis urolepis urolepis in freshwater.
Table 6. Survival rates of T. zillii and O. urolepis
urolepis
Survival
rate
T. zillii in 35% seawater (treatment)
96%
T. zillii in freshwater (control)
89%
T. zillii in 35% salinity (handling control)
82%
O. urolepis urolepis in 35% seawater
(treatment)
100%
O. urolepis urolepis in freshwater (control) 100%
O. urolepis urolepis in 35‰ seawater
(handling control)
90%
Survival rates
The survival of T. zillii and O. urolepis
urolepis is presented in Table 6; the latter
manifested better survival (100%, except
in the handling control) in both fresh and
seawater. This suggests that it is more tolerant
of seawater, once adapted, despite its slower
acclimatization. The mortalities in O. urolepis
urolepis in the handling control ponds may
have been due to accumulated wastes as
the ponds, though flushed, were minimally
disturbed.
Nugon (2003) reported that Oreochromis
aureus, O. niloticus and FRT exhibited
survival rates of ~81% in salinity regimes of
up to 20‰, and lower survival rates for O.
aureus (54%) and FRT (33%) at 35‰ salinity.
The present T. zillii and O. urolepis urolepis
studies yielded better survival rates and
indicated that the environmental parameters
were suitable for rearing the two species.
CONCLUSIONS
Based on the results of this study, both T. zillii and
O. urolepis urolepis can be reared in seawater
but O. urolepis urolepis is more suitable for fresh
water aquaculture. The development of brood
stock of both species would appear advisable
and, if possible, they should be crossbred for
trials of the fingerlings in seawater hatcheries.
The fingerlings could be grown out or used for
feedstock in the numerous milkfish mariculture
ponds in the Tanga Region where there is
scarcity of such food. DNA analysis should
be conducted on both species to confirm their
identification as interbreeding among tilapia
species has been known to produce intermediate
characteristics (Moralee, 2000).
44
A. Nehemia et al.
35
30
T. zillii
O. urolepis urolepis
25
% Weight gain
20
15
10
5
0
0
-5
1
2
3
4
5
6
7
8
9
Weeks
-10
Figure 5. Percentage weight gain of Tilapia zillii and Oreochromis urolepis urolepis in seawater.
Acknowledgements–We would like to thank
the staff and students at the Institute of Marine
Sciences who assisted with data collection
and analysis. Our appreciation is also due
to Swedish International Development
Cooperation Agency (Sida) for financial
assistance.
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Aviti Mmochi