International Journal of Aquaculture, 2015, Vol.5, No.3 1
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production levels when available oxygen present and
unionized ammonia is reduced. Rearing densities of
75 fish/m
3
for fingerling would seem to be the most
desirable in the system studied. There was a strong
trend for both production and final harvest to increase
with increasing stocking density (Fig
ure
3). These
results are in agreement with those of Cruz and Ridha
(1989) from studies on tilapia (
Oreochromis spilurus
)
reared in cages. Our results also agree with Al Jerian
(1998) who reported that production of fish culture are
generally depended on the stocking density, water
exchange, daily feed consumption rate and feeding
frequency. Therefore, the results of the present study
showed that stocking density was positively correlated
with total production per unit area (r = 0.987) and
negatively correlated with individual weight gain (r =
-
0.997).
Water exchange in aquaculture ponds in thought to
improve water quality by providing oxygen enriched
water by diluting excessive concentrations of toxic
metabolites nutrients and plankton (Boyd, 1982). Mc
Gee and Boyd (1983) pointed out that the pond
manager use water exchange in two ways: during an
oxygen depletion, fresh oxygenated water is supplied
to provide oxygen enriched zones near in flow pipes,
which are sough out by fish. Water also, may be
exchanged at intervals in attempts to remove excess
nutrients and plankton resulting from feed
applications.
The carrying capacity of fish in an intensive culture
system is determined by the quality of dissolved
oxygen available to fish. Because the amount of
oxygen available is directly proportional to the
volume of water flowing past the fish an increase in
flow rate leads to a proportional increase in carrying
capacity (Piper et al
.
, 1982). In the present study,
water exchange rates had no significant effects on
growth performances of mono-sex male Nile tilapia
reared in concrete tanks. This is in agreement with that
of Diana and Fast (1989) who reported that water flow
rate had no significant effects on growth and yield of
Clarias fuscus
. In contrast to our results, Siddiqui et al.
(1991) resulted that the growth rate was found to be
directly related to the rate of water flow, and the
amount of water was the limiting factor. They found
the best growth with a continuous flow rate of 1 L/min
per kg biomass. Paspatis et al. (2003) pointed out that
in channel catfish (
Ictalurus punctatus
) culture, the
relation of stocking density and fish growth is
changeable and depends on water exchange rate.
In the present study water exchange rates had no
significant effect on feed conversion ratio. But the
lowest values were achieved at the lowest water
exchange rate. This is in agreement with that of
Siddiqui et al.(1991) who reported that the feed
conversion ratios increased with decreasing rate of
water flow (water exchange) at
O. niloticus
fingerlings
where stocked in 3.75 m
3
out door concrete tanks for
98 days. An experiment was conducted by (Cole, et al
.
1994) to determine the effect of 5% daily water
exchange and no water exchange on tilapia production.
They found that mean growth, yields, survival and
feed conversion were 3.5 g / day, 6.8 kg / m
3
, 97 %
and 1.8 for water exchange tanks and 3.4 g/d, 6.5 kg / m
3
,
95 % and 1.9 for tanks without water exchange. Also,
they pointed out that 5 % daily water exchange did not
significantly improve any of the production parameters.
In the present study, the whole body fat and energy
contents were not significantly affected by stocking
density or water exchange rates. Al Hafedh (1999) and
El-Saidy et al. 1999 reported similar results.
Whole-body protein and ash contents were not
significantly affected by water exchange rates, but
significantly affected by stocking density. Fish
stocked at 50fish/m
3
had a higher percentage of
protein, but lower lipid than fish stocked at 100
fish/m
3
. These results were reported also by El-Saidy
and Gaber (2002a)
Finally, from the above results and the economic
evaluation it can be concluded that a stocking density
of 75 fish/m
3
at either 8L/min. or 12L/min. water
exchange rates is recommended for mono-sex male
Nile tilapia. These fish showed no significant increase
in weight gain with increasing water exchange rates,
but exhibited a significant increase with decreasing
stocking density. Thus a stocking density of 75 fish/m
3
at 8L/min. water exchange rate is cost effective,
highest profit and maintained adequate growth and
production of mono-sex male Nile tilapia in concrete
tanks under the experimental condition.
Refe
rances
Al- Hafedh Y. S., 1999, Effects of dietary protein on growth and body
composition of Nile tilapia (
Oreochromis niloticus
L.), Aquaculture
Research
,
30: 385-393
