Aquaculture is the fastest growing animal production industry in the world; almost every region is experiencing rapid growth in the farming of fish, molluscs, crustaceans and aquatic plants.

1. July | August 2013
Fine particle filtration in aquaculture
The International magazine for the aquaculture feed industry
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3. A
quaculture is the fastest growing
animal production industry in the
world; almost every region is
experiencing rapid growth in the
farming of fish, molluscs, crustaceans and
aquatic plants.
Worth over AUD$200 billion globally, the
aquaculture industry has been growing at a
faster rate than the world’s population for the
past five decades, resulting in a very competi-
tive marketplace today.
Such dramatic growth in the aquaculture
industry has driven trends in filtration and
oxygenation techniques forward to focus
on high efficiency systems which offer fine
particle filtration. This is due to the realisa-
tion that systems chosen purely for their
low cost may not necessarily deliver profit-
able results. The health and growth of your
fish depend greatly upon the filtration and
oxygenation of the water in which they live.
Therefore, it is vital you invest in a quality
system so you can produce large, healthy
fish as quickly as possible to increase your
profit margin.
“The filtration for aquaculture is very differ-
ent to anything else, as you are filtering totally
different material which is much larger in
mass – such as pond weed, fish food and fish
waste,” says Bryan Goh, director, Waterco
Ltd, Australia, an international manufacturer,
which produces a range of filtration solutions
for commercial and domestic systems.
Those using closed systems have taken
particularly to recirculating filtration systems,
which entail the same water being recircu-
lated an infinite number of times after being
properly filtered and slightly topped up to
make up for the water which is lost through
evaporation.
Fine particles are defined as particulate
matter that is 2.5 microns or less in diameter;
therefore, they can be left behind by some
filtration systems that are not designed to
capture particles that small.
Fine particle filtration is important for three
reasons:
1. The amount of waste that fish produce
can quickly destroy water clarity and
reduce the amount of oxygen the fish
can absorb, which in turn lowers their
growth rate. The quicker this waste is
removed; less oxygen will be used by
the bacteria that are breaking it down
2. Substances that are toxic to fish in small
quantities, such as ammonia and nitrite,
need to be removed quickly before they
use up a great deal of the oxygen in the
water and impact on the health of your
fish
3. Large amounts of feed can also intro-
duce waste into the water and encour-
age bacteria growth, which eat up the
oxygen supply that your fish need;
adequate filtration addresses this issue
Types of filtration
The movement towards fine particle filtra-
tion has resulted in a few particular types of
filtration and waste removal systems being
favoured in the aquaculture industry. These
include screens, gravitational settling, sand and
bead filters, flotation/foam fractionation and
centrifuges.
Gravitational settling, also known as sedi-
mentation, is a waste removal system that
depends on the different densities of the
water and waste particles drawing the waste
particles down and out of the tank. However,
waste particles in aquaculture are usually only
slightly denser than the water and so can take
time to settle. Faster separation is achieved
when the density is vastly different; most
aquaculture systems use 15-20 minute reten-
tion times for waste.
Filter screens
Filter screens are a form of mechanical
waste removal. Opening sizes can vary from
Fine particle filtration in aquaculture
by Katie Adema, journalist, Waterco Ltd, Australia
18 | InternAtIonAl AquAFeed | July-August 2013
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5. several millimeters to less than 0.001 micron.
Fine filtration systems, such as microscreen
drum filters which are already commonly
used in aquaculture, typically require much
larger filter screens and/or higher pressures to
operate effectively than a screen with larger
openings.
Centrifuges and hydro clones
Centrifuges and hydro clones are growing
in popularity as they cross from domestic use
into commercial use. Cylindrical in shape, the
mechanism rotates the central chamber very
rapidly, forcing waste particles that are denser
than the water to the sides of the cylinder. A
layer of water from the outer rim is then taken
out, which removes most of the particles with
it, leaving the clean water in the centre to be
put back into the aquaculture system.
Bruce Atkinson, aquaculture design and
sales manager, Aquasonic, Australia, says cen-
trifugal solutions such as Waterco’s new
range of MultiCyclone filters can allow you to
increase stocking rates.
“The link between feed rates and
MultiCyclones is fairly obvious for fish culture
systems,” says Atkinson. “With the addition
of the MultiCyclone, more efficient mechani-
cal filtration takes place and hence greater
volumes of feed can be introduced without
system fouling caused by organic deposition
and bacterial proliferation.
“This means stocking rates can be
increased, with subsequent improved pro-
duction. MultiCyclones in fish culture
systems are best deployed on the
system return pump prior to, say, bag
or cartridge polishing filters on the
way back to the fish tank. ”
Sand or bead filters
Sand or bead filters can be either
fixed bed and particle bed filters that con-
sist of a box filled with sand or another
particulate material. To achieve fine par-
ticle filtration, the filter medium should
be very fine grain and may also need to
be pressurised. Water passes through the
fixed bed either in a downward direction
or and upward direction (down flow and
up flow), and waste particles are removed
by the sand/beads. The size of particles
removed depends on the size of the filter
medium, flow rate and waste characteris-
tics. A sand/bead filter may need frequent
backwashing if waste is very concentrated.
Floatation or foam
fractionation
Floatation or foam fractionation is a
form of chemical filtration; this type of
filtration is able to retrieve very fine
particles from an aquaculture sys-
tem, and is consequently already
Waterco’s
commercial
MultiCyclone
July-August 2013 | InternAtIonAl AquAFeed | 19
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T3 (10 g Hydroyeast Aquaculture®/Kg diet),
which were gave significantly (P ≤ 0.05) final
body weight, AWG, RGR, ADG and SGR
than the control (T1). But, no significant (P
≥ 0.05) differences between T2 and T3 for
final weight, AWG and ADG, as well as in SR
among all treatments.
Female
Data of growth performance parameters
of adult females O. niloticus revealed that
T7 (10 g Hydroyeast Aquaculture®/Kg diet)
was the best treatment followed by T6 (5
g Hydroyeast Aquaculture®/Kg diet), which
were gave significantly (P ≤ 0.05) increased
final body weight, AWG, RGR, ADG and
SGR than T8 (15 g Hydroyeast Aquaculture®/
Kg diet) and the control (T5). However, no
significant (P ≥ 0.05) effects in SR among all
treatments (Table 5).
Feed and nutrients utilization
Male
Results of feed nutrients utilization param-
eters of adult males O. niloticus were shown
in Table 6, whereas T4 gave the highest
significantly (P ≤ 0.05) increased FE, PER and
the best FCR followed by T2 compared with
the control (T1) and T3. In contrast, PPV or
EU increased significantly (P ≤ 0.05) in T1
followed by T2 compared with T3 and T4.
However, no significant (P ≥ 0.05) differ-
ences in FI among all treatments.
Female
Adult females' O. niloticus fed 10 g
Hydroyeast Aquaculture®/kg diet (T7)
showed a significant (P ≤ 0.05) increase in
FI, FE, PER and the best FCR followed by fish
fed 5 g Hydroyeast Aquaculture®/kg diet (T6)
compared with the control (T1). However,
treatment 6 gave significantly (P ≤ 0.05)
increase of PPV and EU among all treatments
(Table 7).
Generally, the differences between males
and females within all treatments concerning,
feed and nutrients utilization parameters may
be due to the differences in sexes, metabolism,
physiological responses and sexual behaviours
of fish during this stage of life.
Fish carcass composition
Male
Proximate chemical analysis of the whole
adult male O. niloticus body at the start and at
the end of the
experiment is
summarized in
Table 8. These
data indicated
that there were
significant (P ≤
0.05) increases
of DM and EC
content in the
control group
(T1) compared
with the dietary
inclusion of
Hydroyeast
Aquaculture®
(T2, T3 and T4),
but CP content
was increased
significantly (P ≤
0.05) in T1 or T2
than the T3 and
T4. However,
an unclear trend
was observed in
EE, where the
increasing in EE
content was not
significant in T1
compared with
T3 and T4 and
significant as
compared with
T2. In contrast, of
these results ash content increased significantly in
T3 and T4 compared with T2 and the control
T1. Generally, proximate chemical analysis of the
whole fish body at the start, revealed higher DM,
EE and EC than in the end of the experiment,
but CP and ash were lower at the start than at
the end of the experiment.
Female
Adult female O. niloticus fed the 5 g
Hydroyeast Aquaculture®/kg diet (T6)
table 9: effects of Hydroyeast aquaculture® probiotic on carcass
composition of adult female O. niloticus
% on dry matter basis
treat. DM CP ee ash eC
at the start of the experiment
24.3 59.2 23.6 17.1 557.5
at the start of the experiment
t5 20.9b 53.9c 26.8a 19.1a 557.7b
t6 22.4a 60.2a 24.1b 15.7b 566.9a
t7 17.1d 55.7b 25.7a 18.5a 557.6b
t8 18.4c 55.6bc 25.7a 18.6a 559.9b
± Se 0.09 0.50 0.44 0.29 2.54
P- value 0.0001 0.0001 0.015 0.0001 0.070
Means in the same column having different small letters are significantly
differ (P ≤ 0.05). DM: Dry matter (%); CP: Crude protein (%); EE: Ether
extract (%); EC: Energy content (Kcal/100 g), calculated according to
NRC (1993); SE: Standard Error
table 8: effects of Hydroyeast aquaculture® probiotic on carcass
composition of adult male O. niloticus
% on dry matter basis
treat. DM CP ee ash eC
at the start of the experiment
25.3 52.2 30.7 16.9 585.1
at the end of the experiment
t1 24.8a 58.9a 25.2a 15.9c 570.4a
t2 20.6b 58.1a 23.8b 18.1b 552.9b
t3 18.2c 55.4b 24.3ab 20.3a 541.8c
t4 17.9c 55.5b 24.8ab 19.7a 547.5bc
± Se 0.19 0.55 0.37 0.35 2.21
P- value 0.0001 0.003 0.123 0.0001 0.0001
Means in the same column having different small letters are significantly
differ (P ≤ 0.05). DM: Dry matter (%); CP: Crude protein (%); EE: Ether
extract (%); EC: Energy content (Kcal/100 g), calculated according to
NRC (1993); SE: Standard Error
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6. used widely. It takes advantage of the surface
tension and charges at the air/water interface,
using bubbles to capture dissolved and very
fine particle matter. In this system, an air stone
in the bottom of a vertical pipe produces
bubbles. As they rise through the pipe they
collect dissolved minerals from the bulk liquid,
and when the bubbles reach the
surface and are removed, so are
the waste particles. It’s a sim-
ple, inexpensive form of filtration
that can also remove dissolved
pollutants from the water. This
removal mechanism is particularly
effective in saltwater applications,
as formation of fine bubbles is
much easier than in fresh water
applications.
It is quite common in aqua-
culture to use a combination
of different filtration and waste
removal systems to achieve opti-
mum water quality.
Oxygen cones
Oxygen concentration is
worth mentioning in relation to
fine particle filtration because the
bacteria that break down fish
waste and leftover feed use up
a great deal of oxygen, which
is paramount to fish health and
growth. The longer this waste is
left in the water, the smaller it
becomes as it is broken down,
causing it to be very difficult to
remove. Therefore, this waste
needs to be removed as quickly
and as effectively as possible
by your filtration system, which
needs to be equipped to handle
very small particles of waste.
After filtration, an oxygen
cone can be used to restore oxygen satura-
tion to optimum levels.
“Oxygen cones have the ability to increase
O² levels in fish culture systems, with increased
levels of O² being of great benefit to fish
health in general,” says Atkinson.
“In experiments carried out on halibut spe-
cies, oxygen saturation levels were
shown to have a positive effect on
the growth and feed conversion
ratio at 80 percent and 120 percent
saturation.
“The conclusion was that the
oxygen saturation levels have a
positive effect on growth and feed
conversion ratios of fish, and in the
case of Atlantic halibut, the growth
rate is higher when the oxygen level
is between 80 percent and 120
percent.”
The correct combination of oxy-
gen, fresh water and food is essential
for fish production, and maintaining
water oxygen levels is a careful
balancing act.
Waterco’s specially created
Oxygen Cone allows the oxygen
levels in water to be managed more
effectively for higher quantities of fish
per volume of water. The industry standard
for most species of fish is up to 50 kg of
stock to 1,000 litres of water; with an oxygen
cone, you can increase your productivity and
stocking rates.
Oxygen cones inject oxygen into the water
delivery line and into the fish culture tanks. The
Oxygen Cone is shaped to optimise the satu-
ration of gases in water - up to 100 percent.
Water and oxygen enter at the top of the
cone at relatively high speed and then the
stream of water pushes the oxygen bubbles
down until they completely dissolve.
“Several studies have investigated the rela-
tionship between oxygen saturation and fish
food intake,” says Atkinson
“In 1976, Randolph and Clemens found
that feeding patterns of channel catfish varied
with temperature and oxygen availability.
When the oxygen content drops below 59
percent, a fish starts to lose its appetite.
Rainbow trout (Oncorhynchus mykiss) appetite
is reduced when oxygen saturation falls below
approximately 60 percent.”
“From these studies, using varied species
it can be concluded that by increasing oxygen
saturation with the use of a saturation ves-
sel such as a Waterco Oxygen Cone, the
farmer can increase his production significantly
and save on food costs as well because of
improved feed conversion ratios.”
More InforMatIon:
Waterco Ltd
Tel: +44 1795 521733
Email: info@waterco.eu
Website: www.waterco.eu
Aquasonic P/L Aquaculture Supplies
Tel: +61 2 6586 4933
Email: aquaculture@aquasonic.com.au
Website: www.aquasonic.com.au
In focus: koi ponds
Although koi ponds are most commonly used as an
aesthetic addition to a backyard, they rely on a delicate
balance of filtration and oxygenation to keep the fish
healthy, just like a tank used for commercial aquaculture.
The large amount of waste these fast growing fish
produce also makes them a good example of the impor-
tance of fine particle filtration and oxygen saturation. A
koi pond usually requires both a mechanical filter and a
biological filter to maintain water clarity and fish health.
A turnover rate of at least 1.5 times per hour will ensure
good circulation, aeration and filtration.
“In many cases, large pre-filter systems are required,
such as vortex chambers and/or sieves as well as a main
filtration system that in many cases is used both as a
mechanical as well as a biological filter. This literally traps
the solid wastes and removes them from the water flow
and provides a large surface area to support the growth
of beneficial bacteria that breaks down pollutants in
the water,” explains Bryan Goh, director, Waterco,
Australia.
“Such filters can be single or multimedia chambers
as well as bead filters. The filtration system is not only
designed based on the volume of water but also the
quantity and size of fish, anticipated feeding cycles and
the amount of fish waste.”
Filtration needs to be backed up with adequate oxy-
gen saturation levels, delivered by oxygen cones, water
plants and/or aeration. One thousand litres of water
saturated with oxygen at 8 parts per million contains
only 8 grams of dissolved oxygen. The health of koi fish
is compromised when oxygen levels fall below 6 ppm,
something that 10 kg of fish which consume about three
grams of oxygen per hour can bring about in about 40
minutes without the help of adequate filtration and
oxygenation.
20 | InternAtIonAl AquAFeed | July-August 2013
FEATURE

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8. www.aquafeed.co.uk
LINKS
• See the full issue
• Visit the International Aquafeed website
• Contact the International Aquafeed Team
• Subscribe to International Aquafeed
Maintaining ingredient
quality in extruded feeds
Fine particle filtration in
aquaculture
Effect of probiotic,
Hydroyeast Aquaculture
– as growth promoter for adult Nile tilapia
Volume 16 Issue 4 2013 - JulY | August
INCORPORATING
fIsh fARmING TeChNOlOGy
EXPERT TOPIC
– channel catfish
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