International Journal of Aquaculture, 2013, Vol.3, No.21, 117
-
125
http://ija.sophiapublisher.com
121
Summerfelt et al., 2004). Other physicochemical
parameters of the pond were pH 6.2-7, temperature
26.2
℃
-26.5
℃
which differed with the work of
Syarikat (2008). Temperature was 29
℃
,
pH 7.7,
Syarikat (2008). Tookwinas and Charearnrid (2008),
obtained pH 7.5-8.3, temperature 26
℃
-32
℃
,
ammonia was less than 0.02 ppm, Tookwinas and
Charearnrid (2008). Ammonia in this work was 0.6
ppm in the two recirculating systems but improved to
0.3
ppm after passing through biofilters and activated
carbon. The oxygen ranges from (5.7-9.4) mg/L
indicated that the aerator system and the biofilter are
technically capable of delivering sufficient oxygen
and removing nitrogenonous waste that could
contaminate water respectively. Critical to successful
operation of RAS is the ability to remove ammonia.
The biofilter system was able to keep ammonia below
0.6
mg/L in the culture tanks. Nitrate, the end product
of nitrification, is relatively nontoxic except at very
high concentrations (over 300 ppm). Usually nitrate
does not build up to these concentrations if some daily
exchange (5 to 10 percent) with fresh water is part of
the management routine. In general, the project
experiment went well as both systems were
functioning in the environment at the facility and
NH3-N levels in the system with biofilter. The more
critical measurement for fish growth is the unionised
ammonia. Pada (2007) recorded ammonia levels 0.005
mg/L for the system without biofilter and 0.015 mg/L
for the system with filter. There was no ammonia in
the inlet water from bore hole water supplying the
whole campus community with drinking water.
Ammonia is the principal nitrogenous waste released
by fish and is mainly excreted across the gills as
ammonia gas. Ammonia is a byproduct from the
digestion of protein. An estimated 2.2 pounds of
ammonia nitrogen are produced from each 100 pounds
of feed fed. Bacteria in the biofilter convert ammonia
to nitrite and nitrite to nitrate, a process called
nitrification. Both ammonia and nitrite are toxic to
fish and are, therefore, major management problems
in recirculating systems. Ammonia in water exists as
two compounds: ionized (NH
4
+
)
and un-ionized (NH
3
)
ammonia. Unionized ammonia is extremely toxic to
fish. The amount of unionized ammonia present
depends on pH and temperature of the water.
Un-ionized ammonia nitrogen concentrations as low
as 0.02 ppm-0.07 ppm have been shown to slow
growth and cause tissue damage in several species of
warm water fish (Michael et al., 1997). The removal
of solid wastes, the uneaten feed and faeces by
biofilter from the culture tank was efficient. However,
wastes that deposit in the joints of the discharge pipe
from the culture tanks to the reservoir tank need to be
removed daily. The wastes that accumulate in the
sedimentation tank need to be flushed out manually.
RAS consists of an organised set of complementary
processes that allow water leaving a fish culture tank
to be reconditioned and then reused in the same fish
culture tank or other fish culture tanks (Liao and
Mayo, 1972; Timmons et al., 2002).
Microbial analysis in the ponds were 2.2×10
3
cfu/mL
3
,
6.8
×10
3
cfu/mL
3
, 1.8
×10
3
cfu/mL
3
for solar powered,
electric powered and UV treatred water. The lowered
microbial count could be due to the fact that the solar
powered were never stagnated as a result of power
failure because there was availability of power all
through the duration of the experiment. The electricity
powered pond suffered from power outages for
between 2 hours-5 hours two times a week. The
pumping of treated water from under ground treated
water to the fish ponds helped in improving dissolved
oxygen in the fish ponds coupled with the fact that the
water was aerated continuously during the period all
these enhanced the dissolved oxygen in the pond and
prevented the organisms from exposure to the
dangerous low level of oxygen. Khleifat et al. (2006)
noted that ultraviolet radiation could eliminate
microorganisms when it is expose to ultra violet
radiation. Eccleston (1998) reported that the UV is
harmful to microorganism and it could improve water
qualities. The UV system has distinct advantages
where waterborne pathogens are a problem (Gadgil
and Shown, 1995).The challenge to designers of
recirculating systems is to maximize production
capacity of capital invested through employing the use
of efficient energy sources to power the systems.
Components should be designed and integrated into
the complete system or existing fish ponds to reduce
cost while maintaining or even improving reliability.
There are many alternative technologies for each
process and operation. The selection of a particular
technology depends upon the species being reared,
production site infrastructure, production management
expertise, and other factors. Prospective users of
recirculating aquaculture production systems need to