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International Journal of Aquaculture 2012, Vol.2, No.9, 59
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64
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62
The best feed utilization efficiency (in terms of feed
conversion ratio, metabolic growth rate and protein
efficiency ratio) of juvenile
Oreochromis niloticus
was
also recorded on the fish reared at 32
℃
followed by
30
℃
. The poorest feed utilization efficiency of
juvenile
Oreochromis niloticus
was achieved by the
fish reared at 24
℃
water temperature. These
indicated that feed utilization efficiency increased
with water temperature increased until 32
℃
and
decreased as water temperature excide. These results
were confirmed the earlier work of Pandit and
Nakaura (2010) who reported the highest feed
conversion ratio was achieved 32
℃
and decreased at
35
℃
and 37
℃
water temperature. Similar results
were reported by El-Sherif and El-Feky (2009a,b).
These authors noted that feed conversion ratio
increased as water temperature increased from 20
℃
to 30
℃
.
The results also revealed that there was physiological
disturbance in the fish reared at 34
℃
water
temperature and had reddish colour around the fines
and operculum which were not occur on the other fish
reared at other rearing water temperature (Britz et al.,
1997; Lei and Li, 2000). Moreover, higher water
temperature initiates early sexual maturation as
compared to lower water temperature. This implies
that there is conflict between growth rate and early
sexual maturation at higher water temperature. In
general as mentioned by Usmani and Jafri (2002),
protein utilisation efficiency is very low at lower
(18
℃
)
and higher 38
℃
water temperature and higher
at optimum water temperature (28
℃
). This implies
that optimum growth of fish can be achieved when
their protein utilisation efficiency high at optimum
water temperature.
3 Conclusions and Recommendation
The present results clearly demonstrated that the
growth performance and feed utilization efficiency of
juvenile
Oreochromis niloticus
reared in aquaria at
different water temperature were significantly (p<0.05)
different in which the fish reared at 32
℃
water
temperature had the highest growth performance and
feed utilization efficiency followed by 30
℃
. The
poorest growth performance and feed utilization
efficiency were observed at 24
℃
water temperature.
It is worth to say that the optimum water temperature
for best growth performance of juvenile
Oreochromis
niloticus
is ranged from 28
℃
to 32
℃
.
This study also demonstrated the possibility of
Oreochromis niloticus
culture in the rift valley region
of the country where the average temperature is above
26
℃
. The overall conclusion is that growth
performance and feed utilization efficiency of juvenile
Oreochromis niloticus
are temperature dependent and
thus, it is crucial to select the right water temperature
for a specific fish species to a particular culturing area.
However, there should be further investigation to
achieve best
Oreochromis niloticus
production by
delaying sexual maturation at higher water
temperature to achieve maximum growth rate.
4 Materials and Methods
4.1 Collection of fish and experimental design
The study was conducted in biology laboratory,
College of Natural and Computational Sciences,
Hawassa University, Ethiopia, using glass aquaria
(80cm
× 30cm × 35cm). The water in aquaria was
aerated by a constant supply of compressed air pump.
The water was changed in two days interval with
100% of water volume with fresh water. Following
aquaria preparation, healthy juvenile of
Oreochromis
niloticus
of mixed-sex was collected from Lake
Chamo. Then, the fish was stocked into
acclimatization aquaria for two weeks until the fish
become more active and stopped mass mortality due
to stress during transportation and handling. After
acclimatization, the fish having an average body
weight of 4.19 g and length of 6.37 cm were stocked
into 50 L glass aquaria at 24, 26, 28, 30, 32 and 34
℃
for 90 days. The stocking density was 10 fish per
aquarium. The temperature was fixed using A 2.0 KW
immersion thermostatic heater to maintain the
preselected water temperatures.
4.2 Feeding and feed supplements
The experimental fish feed was prepared in biology
laboratory from locally available feed. The diet had 27%
crud proteins. The feed was offered for the fish three
times a day at rate of 10% of body weight
(Abdel-Tawwab, 2004). The amount of the feed was
adjusted once in two weeks intervals based on the