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International Journal of Aquaculture 2012, Vol.2, No.7, 40
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47
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45
strain had the highest growth performance and feed
utilization efficiency than the other strains tested. The
poorest growth performance was observed in the
Ziway strain. It is worth to say that the best growth
performed strain (Koka strain) had best feed
utilization efficiency and had the highest gross fish
yield at harvest. This implies that growth performance
of
Oreochromis niloticus
is strain dependent. Thus, it
is very important to select the correct strain to
enhancement
Oreochromis niloticus
aquaculture
production. Therefore, it is recommended that
Oreochromis niloticus
hatcheries should use Koka
strain than other strains tested for fry propagation at
least for similar climate condition. However, further
research may still need to compare more strains at
different life stages as well as at different
environmental conditions with varieties of feed to
evaluate the genetic potential of the strains. Thus, the
expected genetic differences between strains can be
used for establishment of base population that could
be utilized for the development of fish culture and
breeding program.
5 Materials and Methods
5.1 Description of experimental site
The experiment was conducted in National Fishery
and Other Aquatic Resources Research Center
(NFARRC), Ethiopia. The research center is situated
to southwest direction of Addis Ababa, the capital city
of Ethiopia at 24 km. The climatic zone is classified as
mid-altitude zone (2 240 m above sea level).The mean
annual temperature of the area is 21
℃
with an
average annual rainfall of 890 mm (Ashenafi and
Eshutu, 2004).
5.2 Experimental design and juvenile
Oreochromis
niloticus
strain collection
The experiment was designed to investigate the effects
of strain variation on growth performance, survival
rate, feed conversion ratio, growth pattern and gross
fish yield. For this purpose, three similar sizes (10 m ×
10 m × 1.5 m) of ponds were selected randomly. All
the three ponds were cleaned and left for one week for
complete drying. Then, each pond was partitioned into
four parts using nets. All the ponds were filled with
water at 100 cm water. Following pond preparation,
healthy juvenile
Oreochromis niloticus
strains of
mixed-sex were collected from four Ethiopian lakes
(Hawassa, Ziway, Koka and Hora Lakes) by using a
50 m length and 2.5 m width beach sieve mesh whose
stretched length was 20 mm. Immediately after
captured, appropriate size of juvenile
Oreochromis
niloticus
was screened for other species as well as for
large and small size of the same species by hand
picking. Polyethylene bags containing approximately
25 litres of water were used to transport about 200
individuals of juveniles
Oreochromis niloticus
(Ashagrie et al., 2008). Depending on the distance
between the lake and the research center, the fish were
provided pure oxygen more than once using oxygen
cylinder. At the study site, the polyethylene bag
containing the fish was immersed into the pond for
about 20 minutes to acclimatize the fish to the new
water condition. Moreover, the polyethylene bag was
tied off and allowed a flow of water into the bag to
make an equilibrium condition. The fish then swim
and move to the pond. Finally, all the strains of the
fish were stocked into acclimatization ponds for three
weeks until fish become more active and stopped
mass mortality due to stress during transportation.
Dead and weaken fish were removed daily. Then the
fish having an average body length 9.18 cm and
weight 12.48 g were transferred to the experimental
ponds.
5.3 Feeding and feed supplements
The experimental fish were fed twice a day at 10:00
and 17:00 hours with the feed produced by Akaki feed
factory when the daily surface water temperature is
warmer (Tran-Duy et al., 2008). The feeding rate was
3% of the body weight of the fish per day throughout
the experiment (Abdel-Tawwab, 2004). The
nutritional composition of the diet used for the
experiment was 89.69% dry matter which contains
92.18% organic matters and 7.82% ash. The ash also
contains Phosphorus (0.08%), nitrogen (2.2%),
Calcium (0.19%), Magnesium (0.32%), Iron (0.355%),
Potassium (1.09%) and sodium (79.9‰). About 23%
of the organic matter is crud proteins. The amount of
the feed was adjusted once in two weeks based on the
body weight of the fish. Thus the amount of daily
supplementary feed (DSF) was calculated using the
average body weight (ABW), the total number of the
fish (N) and the feeding rate per day (FR /d) using
DSF = ABW × N × FR /d.