Aquaculture systems

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Aquaculture systems
Magdy Abdel-Hamied Soltan
Fac. Agric. Benha Univer. Egypt
Owing to the great diversity of aquaculture operations, the description of types of
aquaculture systems may be complex and sometimes confusing to the novice.
Usually culture systems are classified according to three criteria:
(A) Type of culture structure. Culture structure describes what encloses or
supports the aquaculture organisms. Broadly, aquaculture structures include
ponds, tanks, raceways, cages and pens.
(B) Water exchange. Water exchange describes the amount of water exchanged
or the control over water flow to the system. Broadly, the levels of water
exchange are static, open, semi-closed and recirculating (closed).
(C) Intensity of culture. Intensity of culture reflects the number of aquaculture
organisms per unit area or water volume and also the ability of the natural
productivity to support the crop. Broadly, the intensity of culture is described
as intensive, semi-intensive or extensive.
(D) Fish farming methods. number of fish species reared in the same pond.
The type of system used for aquaculture production is a combination of the above
criteria. For example, there may be a pond system that is:
• extensive and static: to grow major carp in ponds in China and India;
• semi-intensive and semi-closed: to grow silver perch in ponds in Australia;
• semi-closed and intensive: to grow shrimp in ponds in Asia;
• open and intensive: to grow Atlantic salmon in sea cages in Canada.
Aquaculture systems are classified according to the following criteria:
a) Types of rearing facilities (ponds, cages, raceways, pens, enclosure, tank, ..)
b) Water exchange (open or closed).
c) Intensity of culture (extensive, semi-intensive, intensive and high intensive).
d) Fish farming methods (monoculture and polyculture).
(A) Type of culture structure.
1. Earthen ponds earthen ponds consists of:

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• Rearing ponds are larger preferable between 0.5 to 1 feddan in size and 1.25-
1.5 m in depth.
• Auxiliary ponds
1. Ponds for segregation of food stock.
2. Spawning ponds
3. Fry nursing ponds
4. Fry holding ponds
5. Storage ponds for marketable fish
6. Overwintering ponds
They usually much smaller ponds and may serve different functions in different
seasons as, the same, pond may be used for carp spawning in spring, fry nursing in
summer, storage of marketable fish in autumn and fry over-wintering in winter.
Generally, the rearing ponds may constitute about 85% while auxiliary ponds
constitute about 15% of the total pond area of the farm.
2. Raceways
1. The pioneer for intensive production.
2. Usually comprise a parallel sets of a narrow channels constructed in sequential
blocks with two to three raceways sets in series.
3. Typically is about 30×3×1 m they may be smaller or larger.
4. Fast water flow rates.
5. Mainly from cement and may be constructed above or in the ground.
3. Concrete or fiberglass tanks
 Shapes of the tank are often circular, rectangular or oval where enters through
nozzles in a manner that creates a rotary circulation within the tank and discharge
occur through tank center by standpipe or bottom drain surrounded by screen.
 Draining out is designed through a central outlet comprising a standpipe
surrounded by screen.
 Typically circular tanks is 4 m in diameter with a water depth of 0.75 m. the
inflow of water is about 4 l/sec. that enables average stocking densities of 200 kg.

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 Tank hygiene seems to be superior due to self cleaning of the central limit in
practice that realizes the water vortex created by flow rates which may be
strong for the fish.
 Usually maximum stocking rates in tanks where the water is changed every 1-2
hour would around 25-50 kg/m3. With aeration this could be as high as 150 kg/m3.
 The fish are fed complete feed, usually 30-35% crude protein for fish over 50
g average weight.
 Security is much easier with a tank system because production is concentrated
on a small site, which can completely fence in.
4. Floating cages, pens and enclosure:
Floating cages modern cages are floating structures with a net suspended below.
They may be square, rectangular or round. Floating cages may be small and of
limited strength or they may be many thousands of cubic metres in volume and
designed for use in the open water. Cages are used for fish culture in their grow-out
phase, that is the months or years up to their market size.
Pens and Net enclosures (hapas) are used in shallow water, typically in ponds, to
create a restricted environment for culture of fish and some crustaceans. They are
not usually large, being in the order of tens of square metres or less. The walls of
the enclosures may be closely spaced stakes, such as bamboo stems or mangrove
branches, or wire and other mesh. This system of culture is practised mainly in
developing countries. One interesting exception to the shallow water pen is the use
of mesh fences or walls to enclose bottom-dwelling scallops. These pens are of
sufficient height to prevent the scallops from swimming over the wall. They may
use floats to allow the mesh to rise and fall with the tide.
Net enclosure (hapas) usually made from fine nylon, plastic mosquito netting or
cotton mesh. Haps are very easy to manage; because fry cannot escape harvesting is
much easier. Hapas can be any manageable size from 1-40 m3 with a depth of 1-2 m
and suspended on poles. They can be simple squares or rectangles. There are also
more complex designs, some with a series of nets separating brood-stock from fry.
Usual broodstock densities are 2-7 fish/m3, male:female sex ratio of 1:2 to 1:7.
Production rates range from 150 fry/m3/month or 50 fry/female/month to over 880

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fry/m3/month of 300-400 fry/female/month. The main ways to improve productivity are
to clean nets and harvest fry regularly. As with all fry production systems it may also be
worthwhile to rest fish regularly rather than trying to breed from them continuously.
Given the appropriate water circulation by the sufficient depth under the nets (0.6 –
1 m) that allows the water to pass freely to keep wastes away.
(a) Earthen ponds
(b) Raceways
( c ) Concrete tanks
(d) Fiberglass tanks
( e ) Floating cages
( f ) Net Enclosure (hapas)
Fig (1) Type of culture structure

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(B) Water exchange
According to water exchange there are two main systems:
1. Static systems
Much global aquaculture production uses traditional pond culture methods.
These ponds are static, with no exchange of water during the culture period. There
may be some topping up to offset evaporation. Static pond culture is usually
extensive because of major problems in maintaining water quality under conditions
of a large biomass of cultured fish per unit volume of static water. Increasing
biomass requires increasing inputs of fertilizers and supplementary feeds to
maintain productivity. This, in turn, requires management for such water quality
problems as unacceptable levels of nitrogen compounds and low DO levels at
night. With supplementary aeration it may be possible to maintain DO with a
higher biomass and achieve greater productivity. Aerators are, however, often not
available or feasible in rural regions where static pond culture is employed.
2. Open systems
Open system is the use of the environment as fish farm (e.g. cages), i.e. the
culture organisms are confined or protected within the farm in a vast amount of
water (e.g. a lake or an ocean) so that water quality is maintained by natural flows
and processing. There is no artificial circulation of water through or within the
system. Cage system classified as open systems when they are placed within a large
body of water such as an ocean or an estuary. In these cage systems the fish are
generally at high density and artificial feed is supplied. Water quality is, however,
maintained by natural currents and tides. Therefore, these are intensive open
systems. Open systems tend to have low operating costs, as there is no requirement
for pumping. Capital costs vary greatly depending on the type of culture. Seasonal
variation in environment result in large variation in growth rate and this is the most
disadvantages of open system.
3. Closed or re-circulating system
Recirculating systems are usually characterized by minimal connection with the
ambient environment and the original water source. These systems have minimal
exchange of water during a production cycle, hence the description as ‘closed’

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systems. Water is added to offset the effects of evaporation or incidental losses or,
more frequently, to maintain water quality. Some water is dis-charged and replaced
each day in most recirculating tank systems with intensive culture. This arises from
aspects of the regular maintenance system, such as removing accumulated solids from
filters. Water quality in completely closed tank systems with intensive culture is much
more difficult to maintain than in systems in which there is a regular 5% or more
replacement per day. Even with some limited water exchange each day, water quality
within a recirculating tank system will only be maintained by artificial manipulation.
The cost of construction and production in intensive recirculating tank systems
has limited the commercial development of these systems for grow-out production.
However, the possibility of high yields with year-round production close to markets
drives their development.
The artificial means of waste processing and some typical components used in
recirculating systems are shown in Fig. (2) Feed input, animal metabolism, wasted
feed and feces production all impact upon water quality.
Parameters that require regulating in an intensive recirculating tank system are:
• particulate matter (settleable, suspended and fine waste solids) in the system
resulting from feed and feces;
• nitrogenous wastes (un-ionised ammonia, ionized ammonia, nitrite and nitrate,
which are often expressed as NH3-N, NH4-N, NO2-N and NO3-N, respectively);
• dissolved gases (O2, CO2 and N2);
• pathogens;
• pH and alkalinity.
At high stocking densities without recirculation technology, a water exchange in
excess of 100% per hour would be required to maintain water quality during
maximal production. In recirculating tank systems, water quality is maintained by
pumping the culture water through specialized filtration and aeration equipment.
Advantages of closed systems
1. Easily harvesting.
2. High stocking density.
3. Require minimal water
4. Food and drugs can be added efficiently into the system

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5. Complete control of water condition
Disadvantages of closed systems
1. High capital coast
2. Require very careful management
3. Rapid spread of disease.
Components of recirculating tank systems:
- Waste solids filtration
Fish wastes such as feces, uneaten feed and ammonia must be regularly removed
from the tanks water in order to avoid its toxicity. The method used for removal of
solid wastes depends on the type of waste. Settleable solids sink and may be
removed by gravity and flow on a continuous basis or by siphoning on a regular
basis. Alternatively, settleable solids can be kept in suspension with continuous
agitation from aeration, water flow and stock movement, and removed using a
mesh screen or allowed to flow into settlement basins or tanks. Settleable solids can
also be removed by centrifugal force using a swirl separator or hydrocyclone.
Suspended solids that will not settle out by gravity are generally removed from
recirculating tank systems using the following mechanisms:
1. Screen filters are made of a fine mesh through which water flows and the
suspended solids are retained on the screen. The screen filters are then
continuously cleaned. Types of self-cleaning screen filters include rotating screen
filters and rotating drum filters.
2. Particulate filters include sand filters and expandable granular media filters.
Particulate filters also require cleaning, a process known as ‘backwashing’.
3. Foam fractionators (or protein skimmers) are used to remove very fine suspended
solids and dissolved organic compounds (DOCs) that cannot be removed by
mechanical filtration in recirculation systems. Air is injected into the bottom of
the vertical fractionator column, usually through a venturi system, forming fine
bubbles which rise up to create a foam at the surface. This waste foam is then
collected and removed. Foam fractionation works through the physical
adsorption (bonding) of the DOCs to fine bubbles as they rise through the
fractionator column. The efficiency of the removal of DOCs and fine suspended

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solids depends on the size of the air bubbles (the smaller the better) and contact
time (the longer the better). Increased contact time is usually achieved with a
counter-current design.
- Ammonia and nitrite removal
There are numerous technologies available for removing ammonia from water
(denitrification), including air stripping, ion exchange, biological filtration and
removal by algae. Air stripping requires the water pH to be adjusted to 10 prior to
stripping and then readjusted to culture levels near 7 prior to water re-entering the
rearing tanks. Ion exchange technology is costly. For these reasons, biological
filtration is still the most widely used method. Biological filters are available in a
variety of forms including trickle filters, submerged filters, rotating biological
contactors, packed tower filters and fluidized bed filters. The objective of
biological filters is to optimize the surface area available for denitrifying bacterial
attachment and flow through the filter across the bacteria. These bacteria, chiefly
species of nitrosomonas and nitrobacter which can be grown on almost any coarse
medium and occur in soil and water environment, they can be easily inoculated into
the biofilters. Firstly, transformation of ammonia to nitrite, then a further oxidation
of nitrite to nitrate. Nitrite is also toxic to fish at low concentration, so that both
reactions must occur.
Nitrosomonas
NH4+ + 3O2 2NO2- + 4H+ + 2H2O
Ammonia Nitrite
Nitrobacter
NO2- + O2 NO3
Nitrite Nitrate
Aerobic conversion of ammonia into nitrates by nitrification bacteria
- Dissolved oxygen
Aeration is the dissolving of oxygen from the atmosphere into water. It is an
important aspect of recirculating tank systems, as it is necessary to maintain
dissolved oxygen at the required level for the cultured animals. It is also important
to maintain dissolved carbon dioxide below 20 mg/L to ensure favorable pH,

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reduce stress and maximize growth. Several types of aeration devices are
commonly used in recirculating tank systems, including diffuser aerators,
mechanical aerators, vertical pump aerators and packed column aerators.
Oxygenation is the process of pure oxygen transfer to water and is used when
oxygen consumption is greater than the capacity to transfer oxygen through
aeration using air (which is only 21% oxygen). Oxygen can be supplied as
compressed oxygen gas and liquid oxygen from commercial sources or it can be
produced on-site by oxygen generators. The choice is generally one of cost and
reliability of electricity supply to produce oxygen on site. As the transfer of gas to
water using diffusers is poor (less than 40% for oxygen), specialized components to
deliver oxygen to recirculating tank systems have been developed. These
components can effectively transfer more than 90% of oxygen to the water. A
variety of oxygenation devices are available.
- Pathogens
Continuous disinfection of water in a recirculating tank system can help to limit
the introduction and spread of disease, and the build-up of pathogenic bacteria, e.g.
Vibrio species, to levels at which they cause mortality in the stock. Ultraviolet
(UV) irradiation and ozonation are two methods of continuous disinfection used in
recirculating tank systems. This section has dealt primarily with recirculating tank
systems used for intensive culture, but larger-scale recirculation systems are now
being developed for pond culture. In ponds with intensive culture, e.g. shrimp
culture, it is difficult to operate without regular water exchange. However, pond
systems in which there is very limited or no water exchange throughout a growing
season are now being developed.
- Buffering pH
Preferred pH for most aquaculture species ranged from 6.5 while some species
can tolerate pH ranged from 5-10 in re-circulating systems. Fish metabolism and
bacteria nitrification of acids that lessen the buffering capacity and lower the pH.
To replace the last alkalinity and sustain the buffering capacity of water
bicarbonate of soda or others is added. Also, the biofilter media (e.g. oyster shell)
or other component of the system (e,g. concrete tanks serves as a source of

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carbonate. Monitoring of water hardness, alkalinity and pH may be required
depending on the species cultured.
( C ) Intensity of culture (fish intensification)
Intensity of aquaculture describes the various densities of organisms per unit
volume or per unit area. It is meaningful in comparisons between the levels of
culture of a species or related species. It is, however, meaningless in terms of
comparisons of densities of organisms from different groups. For instance, culture
of tilapia at 100 kg/m3 of water in a recirculating system is considered to be
intensive culture; culture of shrimp at 50 individuals per m2 (1–2 kg/m3) in ponds is
considered to be intensive culture. Intensity of culture will broadly consider the
inputs into the system to maintain adequate growth of the cultured organisms. It
comes under the term ‘intensity’ because the greater the intensity (or density) of
cultured organisms the greater the requirement for inputs into the system.
The goal of intensification is to obtain higher yield from the same or a smaller
area, water and labour inputs. These systems based on the following principles.
1. Pond aeration of the pond and increase water flow as a means of enriching the
pond with oxygen.
2. Feeding with protein rich pellets.
3. Increasing the stocking density of various fish species.
1. Extensive (conventional) system:
Extensive aquaculture differs markedly, largely being part of a natural ecosystem
and depending upon it for maintenance of water quality and most of the animal's
food and other requirements. An extensive aquaculture system, therefore, has limited
inputs to maintain fish growth and survival, i.e. it may have some basic organic
fertilizers, but no aeration, etc. These systems usually have a low stocking density,
(<500 kg/ha), and the natural productivity of feed (plants and animals) within the
system and natural gas exchange is sufficient to support the cultured organisms. Low
intensity aquaculture yielding only moderate increase over the natural productivity.
Fish feed only the natural food available in the pond.
2. Intensive system:
High intensity aquaculture yielding a far excess over the conventional culture. The

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stocking rate is much higher, at least about 50% of the pond area must be covered
with aeration facilities. Fish feeding depends only on the complete diets (protein-
rich diets). Intensive systems may be in:
• ponds (e.g. for shrimp in tropical/subtropical regions);
• cages (e.g. for marine fish culture in temperate waters);
• raceways (e.g. for trout species in temperate regions);
• tanks (e.g. for eels in Japan).
The peak stocking density achieved in each case depends upon being able to
maintain the water quality conditions required by the cultured organism. Generally,
stocking densities are lowest in ponds, followed by cages and with greatest
densities achieved for raceways and tanks.
Intensive aquaculture systems are a complete contrast to natural systems. They are
characterized by:
• very simple food chains: feed → cultured organisms;
• low energy losses from feed input, with high food conversion ratios from
specialized artificial feeds;
• no recycling of energy and totally non-self-supporting;
• the requirement for high inputs of energy (e.g. feed, nutrients, aeration,
filtration, pumping);
• high yields per unit area or volume.
Water quality is usually maintained by high water exchange rates and, in some cases,
by mechanical means. In intensive culture in indoor tanks, particulate waste removal,
gas exchange and oxygen production are all undertaken by mechanical means. In
outdoor intensive systems with a soil substrate and phytoplankton there is settlement
of particulate wastes, decomposition by bacteria and gas exchange enhanced by
mechanical aeration. Stocking density (mass of culture stock per volume or area of
water, expressed as kg/m3 or kg/ha) in intensive systems varies greatly with the type of
system and the cultured organism, but is always relatively high.
3. Semi-intensive system:
Semi-intensive culture is almost exclusive to ponds and allows for an increase in
the stocking density within the pond. With moderate intensity, fish culture where

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the stocking rate may be 2-3 times as that of the conventional ponds. addition of
inorganic or organic fertilizers to improve natural productivity, addition of aeration
to maintain dissolved oxygen levels and thee aerated area must cover about 10-15%
of the pond area. Supplementary feed must be added beside the natural food
available in the pond. The semi-intensive culture of tilapias is particularly ideal in
developing countries because it provides a wide variety of options in management
and capital investments. Management strategies in lower levels of intensification
involves the use of fertilizers to encourage natural productivity and to improve the
levels of dissolved oxygen. The stocking rate is ranged between 5-10 fish m3. Fish
yields from such techniques have been found to be higher than those from natural
unfertilized systems.
A comparison of coast and returns from the three systems:
1. In conventional system the maximum yield reach about 0.5-1 ton/feddan were
not economic.
2. The semi-intensive system gives moderate net profits.
3. Intensive system is not economic unless the yields exceed 10 tones/feddan due
to the very high cost input for construction.
(D) Fish farming methods
1. Monoculture
Monoculture, the culture of individual of one specie from the same age,
monoculture is the only method of culture used in running water system, re-
circulating system and in cages where the supply of natural food is limited. Under
the conditions of pond culture with fertilization monoculture of single fish specie,
the natural food available in the water column is not fully consumed by fish,
therefore a combination of fish species differ in their feeding habits is preferred.
The following are the drawbacks:
1. Common carp fry depend mainly on the natural food, thus in high densities the
natural food is not enough and reduces fish growth.
2. The problem of filamentous algae in tilapia can be overcome by introducing
about 29% percent of carp in tilapia culturing farms.

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3. Also, in carp monoculture, it is recommended to introduce a number of tilapia
as tilapia consumes part of accumulated organic matters and thus maintain the
oxygen balance in the pond.
4. So some described the monoculture as a bi-culture system.
2. Polyculture
The most important consideration in polyculture is the probability of increasing
fish production by better utilization of natural foods. Species successfully stocked
together are differ in their feeding habits and occupy different trophic niches in the
pond. Tilapia species, common carp, sliver carp and grey mullet are different in their
feeding habits. Polyculture of common carp with all-male tilapia, and sometimes also
with silver carp is a common practice in Egypt. Both tilapias and silver carp graze on
algae, and thus help to maintain a balanced biological environment in which algal
blooms are rare. All-male tilapia in polyculture with marine and/or fresh-water
prawns (Macrobrachium rosenberghii), also produce a more balanced biological
environment in ponds than monoculture of prawns alone.
The synergistic effect lies on:
1. Improving of pond oxygen regime occurs, as in case of silver carp and tilapia.
Silver carp consumes excess algae and this improves the balance between
production and consumption of oxygen. Tilapia feed on the organic ooze of the
pond bottom, this ooze increase oxygen consumption when decomposed by
bacteria thus tilapia improves oxygen in the pond.
2. Some fish feed on the excreta of other fish, as tilapia feed on the excreta of
common carp, which feed on the excreta of silver carp. The latter do not digest
all algae which feed and the larger algae become available to common carp,
which cannot consume all free algae in the water. In general terms tilapia
represents 65%, common carp 23%, grey mullet, 7% and silver carp 5%.
Negative effects lies on:
1. Not all the cultured fish species reach the marketable size at the same time.
2. Sorting of the different species after harvesting is difficult and expensive.

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Integrated fish farming
Integrated fish farming is a system of producing fish in combination with other
agricultural/livestock farming operations centered around the fish pond. The farming
sub-systems e.g. fish, crop and livestock are linked to each other in such a way that
the byproducts/wastes from one sub-system become the valuable inputs to another
sub-system and thus ensures total utilization of land and water resources of the farm
resulting in maximum farm output with minimum financial and labour costs.
(A) Rice-Fish Farming
Rice fish farming is a good technique for rice and fish farming. Hidden safely from
birds and other predators, this fish grow in the thick rice plants, at the same time
provide fertilizer with their compost, eat insect and pests that is risky for rice plants as
well aid the rice field in circulating the oxygen. Rice and fish farming can increase rice
production by 10% in addition they have extra source of food necessity.
As regards the general scale of rice-fish culture, China is the main producer with
an area of about 1.3 million hectares of rice fields with different forms of fish
culture, which produced 1.2 million tonnes of fish and other aquatic animals in
2010. Other countries reporting their rice–fish production to FAO include
Indonesia (92 000 tonnes), Egypt (29 000 tonnes), Thailand (21 000 tonnes), the
Philippines (150 tonnes) and Nepal (45 tonnes).
Benefits
1. It used perfectly the available ground.
2. Production of cheaply animal protein of low cost.
3. Rice–fish farming provides additional food and income.
4. It create hygienic medium through control of molluscus and harmful insects.
5. Increase rice crop by about 5-15% through controlling weed and algae, which
compete with rice and help in fertilization of rice field by their excreta.
6. Biologically control of belharziasis and maralaria through control of mollusks
and culicoids bed.
7. Evidence shows that although rice yields are similar, the integrated rice–fish
system uses 68 percent less pesticide than rice monoculture.

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8. Fish feed on rice pests, thus reducing pest pressure and farmers are much less
motivated to spray pesticides.
9. Complementary use of nitrogen between rice and fish resulted in 24 percent
less chemical fertilizer application and low nitrogen release into the
environment, suggesting positive interactions in the use of resources.
10. Fertilizers and feeds used in the integrated system are more efficiently
utilized and converted into food production, and nutrient discharge to the
natural environment is minimized.
11. Continued flooding and rooting activity as well as fish helps to stir up the
nutrients of the soil that makes them more accessible for rice.
This improves the production of rice.
Disadvantage of simultaneous method:
1. Water flow must be greater than would be necessary just for rice and this
limits the spreading of fish cultivation.
2. It needs a deeper water level, which cannot be tolerated by most varieties of
rice.
3. Dikes, draining ditches and capturing sump take up space from the planned
field.
4. Certain soil cannot be kept under water for prolonged period.
5. Limits the use of agriculture technique as mechanization, fertilization,
herbicides and insecticides.
Challenges
The challenges related to rice–fish farming are not different from those related to
general aquaculture development. They include availability of and access to seed, feed
and capital as well as natural risks associated with water control, disease and
predation. Freshwater is rapidly becoming one of the scarcest natural resources, and
competition for freshwater is among the most critical challenges facing developing
countries. Sufficient and good-quality water is a key resource in rice–fish farming,
which increases the productivity per unit of water used. Rice–fish farming and other
forms of aquaculture in rice-based farming are one component of integrated water
management approaches that produce food of high nutritional quality and, often, high

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economic value. Profits vary depending on production characteristics but income
increases of up to 400% compared with rice monoculture have been reported and these
may be even greater where high-value aquatic species are farmed.
Construction
To start with, practical actions is essential for a farmer to know a appropriate
site: you need to find a place which is not flood prone to prevent your rice fish
farming from washed out. Create a dyke about 60 cm high about the field outskirts.
This is a double purpose method, to keep farmed fish in the field as well as allow
vegetable nurturing about the rice field. Digging a channel is the next step; this is to
provide fish a sanctuary during dry season.
Fig (2) Rice-Fish Farming
Characters of fish adapted to culture in rice fields:
1. Able to withstand shallow and muddy water.
2. Tolerate high temperature.
3. Have high higher growth rate.
4. Tolerate low dissolved oxygen.
5. Without tendency to escape such as tilapia and common carp while grass carp
must not be used because it can eat rice plants.
Stocking and planting:
The rice plants by the planter are in rows which are about 35 cm away from each
other manuring can be applied by spreading about 20 kg of cattle manure or 10 kg

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of chicken manure/feddan over the surface of ditch bottom. The plot then filled
with water and after the water turns greenish it becomes ready to fish stocking.
Fry or fingerlings bags should be put in the ditch for about 15 minutes for
acclimatization, after that the bags are opened in a way enables the water to enter
them gradually and fingerlings escape from the bags into ditch water. Once the rice
begins to grow, the amount of water across the rice field is maintained at 12 up to
15 cm, and fingerlings are free into the channel. For production of marketable size,
the water level maintained at this level for 5 months.
Harvesting
At the end of growing period (3-4 months) water must be drained to help the
ripping of rice and cultured fish are accumulated in the ditch by decreasing its
water level to about 25 cm and this makes it easier to catch fish by small net.
(B) Duck-fish Farming System
In this system duck house is built on the pond to allow manures to fall directly
into the pond or it is located on the dike and manure is daily washed. Since ducks
eat small fish, a fence is used to confine the ducks within certain shallow water
area. Size of fingerling stocked is usually 5-10 cm long. Recommended fish species
are tilapia or tilapia and common carp and mullet at the stocking density of 6,000
5-cm fingerlings/feddan.
Advantages to fish culture sub-system
 Ducks are the “volunteer aerators” while swimming and chasing each other in
the pond.
 The droppings of duck, distributed all over the pond surface, has high nutrient
value and which act as manure and fish feed.
 Spilled over duck feed are also good food for fish.
Advantages to duck rearing sub-system
 Fish pond provide an excellent environment for duck.
 No additional land is required for housing ducks.
 Duck can collect considerable part of their nutrient requirements from the pond
by means of eating tadpoles, unwanted fish fry, insects, snails etc.

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There are three duck culture methods generally used for integrated fish farming:
a. Extensive raising, in which the simple, low productive local variety of duck is
used just for family consumption. The ducks are given free range to search
their own food from the surroundings. The living area is thus not limited to the
fish pond. In this case duck sub-system hardly supports the fish sub-system.
b. Semi-intensive raising, in which the egg laying ducks are fed at the same rate
as on land and kept at a relatively high density per unit of pond area.
Therefore, higher amounts of manure and uneaten duck feed (estimated to be
10 %) usually fall into the fish pond and consequently higher fish yields can
be obtained. However, high priced balanced feed is required to maintain the
egg production resulting in relatively higher cost of production which is
difficult to be compensated by the sale of eggs in rural areas.
c. Intensive raising, in which the ducks are kept at a high density in closed
conditions. The wastes regularly go into the fish pond. However, high cost of
infrastructure, unavailability of balanced feed on commercial scale, need for
high level of hygienic conditions etc.
Duck rearing facilities
Most duck houses in the tropics are built on the pond dyke rather than over the
pond surface since construction costs are less and management is easy. They are
simple shelters which provide shade from the sun and protection from heavy rain
while allowing ample circulation of fresh air. Side curtains may be required to
prevent wind driven rain. Duck houses should be built with local materials such as
bamboo for the frame and bamboo matting for the roof. Ducks apparently do not
like wire floors, unlike chicken. They cannot grasp the slats with their feet and their
feet are very sensitive to damage. Cement floor may also lead to cracked eggs.
Meat ducks may be raised on an earth floor but egg layers need dry grass or hay to
keep the eggs clean and prevent from cracking.
Ducks can be fed and sheltered either on floating rafts or shift structures built
over the pond surface. In both cases the faecal material and uneaten food fall
directly into the pond. The house should be well protected from predators. The
height of the house should be 4–5 ft. The area of house will depend on the number

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of ducks to be kept. Normally 4 sft. of space is required for each bird. It has been
estimated that 30–35% of the dry feed consumed by the ducks is voided as manure
and that only 50–60% of the manure goes into the pond water if the ducks are
housed on the dyke. By housing the ducks over the pond the costs of collecting,
storing, and transporting manure are eliminated and the potential problem of
environmental pollution by the manure are solved. The fish would also be able to
consume the estimated 15% of granulated feed spilled by the ducks during feeding
which would otherwise not be utilized if the ducks were fed on the dyke. It may be
worthwhile to construct floating resting and feeding places on the pond surface if
ducks are housed on the dyke to increase the efficiency of recycling the manure and
the spilled feed. Ducks cause severe erosion of fish pond dykes by climbing into
and out of the water which has two adverse effects: destruction of the dike, and
increased turbidity and siltation of the pond which reduces light penetration and
thus the amount of photosynthesis taking place in the water column. If the duck
house is located on the dike, a ramp is required for easy access.
Duck house on the dyke and feeding platform on the pond water
Selection and stocking rate of fish species
 The selected species should be compatible with each other.
 The species and their combination ratio should be adjusted according to the
amount of feed stuff and manure that are expected to be made available by the
other sub-system.
 As far as possible the species should fast growing.
 Selected fish should be hardy and resistant to common diseases and parasites.

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 The species should be able to tolerate low oxygen levels and high organic
content in the water.
Nursing of young ducklings
Day-old ducklings require controlled environment (temperature, feed, drinking
water and space) up to 2–3 weeks, after which they can be housed near the pond.
During the first week, 50-55 ducklings can be reared per m2 within a heated room,
with a screen floor (1-5 cm mesh, 2mm gauge) to allow manure and uneaten food to
fall through. Pelleted starter feed is provided in demand feeders, with clean taped
water in troughs which are designed to allow access to the beak only, preventing the
ducks from getting wet. Air temperature should be maintained around 30-32°C. After
the third or fourth day, ducklings are released into a small enclosed pen during good
weather and provided with shallow splashing pools to acclimatize them. Special care
should be taken to prevent feed sticking to the heads and backs of the ducklings.
Stocking density and ratio
For a 1 feddan fish pond, 400-500 egg laying ducks are recommended. One-
day-old ducks are bought and raised to one-month-old before stocking in the duck
house. After 4–5 months the ducks start laying eggs. A feed mixture of 15% broken
rice, 30% rice bran, and 20% concentrated feed is applied at 150 gm per duck per
day. About 10% of their feed is washed into the pond, serving as feed for the fish.
Ducks also feed on natural food in shallow water and by feeding on small plants
help control plant density and in turn the oxygen level in the pond. Ducks also eat
small molluscs which are parasite carriers.
For fertilized egg production, 1 male: 5 female ratio is normal. While for
commercial egg production the ratio of 1 male to 10-15 female would be better.
Duck feeds
Besides the limited amount of supplementary feed, the duck will consume frog,
tadpole, mosquito and dragon fly larvae, and aquatic weeds which are generally not
eaten by commonly stocked fish. With simplified semi-intensive rearing of ducks
in ponds at relatively low densities, the protein content of supplementary feed can
be lowered from the 18–19% digestible protein (required if raised in crowded pens)

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to about 11–13%. Pond water also helps to reduce heat stress which enables the
ducks to keep up their feed intake.
Giving 50-100 g crushed fresh snail daily is highly recommended. Duck weed is
also preferred by ducks. Daily 125-130 g supplementary feed per duck seems
sufficient for the adult layers when they have enough natural feed in the pond.
Ducks prefer wet mash due to the difficulties in swallowing dry mash. Initially
the duckling should be fed 4–5 times a day. Later it can be decreased until twice a
day. For adults 10cm feeder length can be used for each duck. If feeding on the
pond is not possible then drinkers should be placed next to the feeders. Feeders and
drinkers should be cleaned every day and dried to prevent from contamination. In
daily feeding, it is better to feed the ducks by the same person.
Diseases
Duck diseases are similar to chicken but ducks are more resistant to most
common diseases. However, vaccination against some of the common epizootics
should be done.
( C ) Chicken-Fish Farming System
Intensive production of broiler meat and egg is now common in many parts of
the world. In integrated fish-poultry farming system the birds are typically fed
complete diets in pelleted or mash form and the manure is used fresh or as dried
poultry waste. The waste recycling is the key feature of the system, and integration
of fish culture with poultry raising is one of the best ways of poultry waste
management.
The digestive tract of a chicken is very short, only 6 times its body length.
Therefore, some of the eaten foodstuff are excreted by the chicken before being
fully digested. Research has shown that about 80 percent (by dry weight) of feed
stuff is utilized and digested by the poultry, leaving 20 percent for use by the fish in
the integrated fish culture system. Chickens while peaking, scatter about 10% of
their food over the ground. This wasted feed is utilized directly by fish. The total
protein content of dry chicken excrement can be as high as 30 percent. Usually,
good chicken feedstuffs have a protein content over 18 percent

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Housing and stocking density
In chicken-fish system the pond is rectangular in shape with 1.5 m water depth.
Chicken house is built above the pond floor 1.2 m above the water level. When
raising broilers, the recommended stocking rate is 3,000 birds/feddan. The farmer
starts with 1 day old chicks and those feed on concentrate feed can attain 1.5–1.9
kg in 50 days. In case of egg laying chicken confined in a small row-cage in the
house, recommended stocking rate is 200 birds per flock for 5 flocks in a year (550
birds/flock/feddan).
Recommended fish species are tilapia or tilapia poly-cultured with catfish, which
have high tolerance to low oxygen level, at a stocking rate of 6,000
fingerlings/feddan). Fish yield is as high as 3,500 kg/feddan in case of tilapia poly-
cultured with catfish since catfish can feed better on the nutrients in the pond.
Tilapia monoculture yields are lower, i.e. 1,700 kg/feddan.
Chicken houses on fish pond
Benefits of fish-chicken integration
Following are some of the additional advantages when fish culture is integrated
with chicken raising on/or near the pond dykes:
 The direct discharge of fresh chicken manure to the fish ponds produces
enough natural fish feed organisms without the use of any additional fertilizer.
 The transportation cost of the manure is not involved.

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 The nutritive value of applied fresh manure is much higher than dry and mixed
with bedding materials e.g. saw dust or rice husk.
 Some parts of the manure is consumed directly by the fish.
 No supplementary feed is needed for the fish.
 No extra space is required for chicken farming. Chicken sheds can be
constructed over the pond water or on the dyke.
 More production of animal protein will be ensured from the same land area.
 The overall farm production and income will increase.
(D) Aquaponics
Aquaponics refers to and system that combines aquaculture (raising aquatic
animals such as fish, crayfish or prawns in tanks with hydroponics (cultivating
plants in water in a symbiotic environment). In normal aquaculture, excretions from
the animals being raised can accumulate in the water, increasing toxicity. In an
aquaponic system, water from an aquaculture system is fed to a hydroponic system
where the by-products are broken down by Nitrifying bacteria into nitrates and
nitrites, which are utilized by the plants as nutrients, and the water is then re-
circulated back to the aquaculture system.
Parts of aquaponic system
Aquaponics consists of two main parts, with the aquaculture part for raising
aquatic animals and the hydroponics part for growing plants. Aquatic effluents,
resulting from uneaten feed or raising animals like fish, accumulate in water due to
the closed-system recirculation of most aquaculture systems. The effluent-rich
water becomes toxic to the aquatic animal in high concentrations but this
contains nutrients essential for plant growth. Although consisting primarily of these
two parts, aquaponics systems are usually grouped into several components or
subsystems responsible for the effective removal of solid wastes, for
adding bases to neutralize acids, or for maintaining water oxygenation. Typical
components include:
 Rearing tank: the tanks for raising and feeding the fish;

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 Settling basin: a unit for catching uneaten food and detached biofilms, and
for settling out fine particulates;
 Biofilter: a place where nitrification bacteria can grow and convert ammonia
into nitrate which are usable by the plants;
 Hydroponics sub-system: the portion of the system where plants are grown
by absorbing excess nutrients from the water;
 Sump: the lowest point in the system where the water flows to and from
which it is pumped back to the rearing tanks.
Depending on the sophistication and cost of the aquaponics system, the units for
solids removal, biofiltration, and/or the hydroponics subsystem may be combined
into one unit or subsystem, which prevents the water from flowing directly from
the aquaculture part of the system to the hydroponics part.
Live components
An aquaponic system depends on different live components to work successfully.
The three main live components are plants, fish (or other aquatic creatures) and bacteria.
Some systems also include additional live components like worms.
1. Plants
A deep water culture hydroponics system where plant grow directly into the
effluent rich water without a soil medium. Plants can be spaced closer together
because the roots do not need to expand outwards to support the weight of the
plant. Many plants are suitable for aquaponic systems, though which ones work for
a specific system depends on the maturity and stocking density of the fish. These
factors influence the concentration of nutrients from the fish effluent, and how
much of those nutrients are made available to the plant roots via bacteria.
Green leaf vegetables with low to medium nutrient requirements are well
adapted to aquaponic systems, including tomatoes, cucumbers, and peppers, have
higher nutrient requirements and will only do well in mature aquaponic systems
that have high stocking densities of fish. Plants that are common in salads have
some of the greatest success in aquaponics, including cucumbers, shallots,
tomatoes, lettuce, chiles, capsicum, red salad onions and snow peas.

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2. Fish (Main article: Aquaculture)
Freshwater fish are the most common aquatic animal raised using aquaponics,
although freshwater crayfish and prawns are also sometimes used. There is a branch of
aquaponics using saltwater fish, called saltwater aquaponics. There are many species
of warm-water and cold-water fish that adapt well to aquaculture systems.
In practice, tilapia are the most popular fish for home and commercial projects
that are intended to raise edible fish because it is a warm water fish species that can
tolerate crowding and changing water conditions. For temperate climates when
there isn't ability or desire to maintain water temperature, bluegill and catfish are
suitable fish species for home systems. Koi and goldfish may also be used, if the
fish in the system need not be edible. Other suitable fish include channel
catfish, rainbow trout, perch, common carp and striped bass.
3. Bacteria
Nitrification (the aerobic conversion of ammonia into nitrates) is one of the most
important functions in an aquaponics system as it reduces the toxicity of the water for
fish, and allows the resulting nitrate compounds to be removed by the plants for
nourishment. Ammonia is steadily released into the water through the excrete and gills
of fish as a product of their metabolism, but must be filtered out of the water since
higher concentrations of ammonia (commonly between 0.5 and 1 ppm) can kill fish.
Although plants can absorb ammonia from the water to some degree, nitrates are
assimilated more easily, thereby efficiently reducing the toxicity of the water for
fish. Ammonia can be converted into other nitrogenous compounds through combined
healthy populations of Nitrosomonas, bacteria that convert ammonia into nitrites and
Nitrobacter, bacteria that convert nitrites into nitrates.
Hydroponic Subsystem (Main article: Hydroponics)
Plants are grown as in hydroponics systems, with their roots immersed in the
nutrient-rich effluent water. This enables them to filter out the ammonia that is
toxic to the aquatic animals, or its metabolites. After the water has passed through
the hydroponic subsystem, it is cleaned and oxygenated, and can return to the
aquaculture vessels. This cycle is continuous.

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Simple diagram aquaponic unit
Biofilter
In an aquaponics system, the bacteria responsible for the conversion of ammonia
to usable nitrates for plants. The submerged roots of the vegetables combined have
a large surface area where many bacteria can accumulate. Together with the
concentrations of ammonia and nitrites in the water, the surface area determines the
speed with which nitrification takes place. Care for these bacterial colonies is
important as to regulate the full assimilation of ammonia and nitrite. This is why
most aquaponics systems include a biofiltering unit, which helps facilitate growth
of these microorganisms. Typically, after a system has stabilized ammonia levels
range from 0.25 to 2.0 ppm; nitrite levels range from 0.25 to 1 ppm, and nitrate
levels range from 2 to 150 ppm.
Water usage
Aquaponic systems do not typically discharge or exchange water under normal
operation, but instead recirculate and reuse water very effectively. The system
relies on the relationship between the animals and the plants to maintain a stable
aquatic environment that experience a minimum of fluctuation in ambient nutrient
and oxygen levels. Water is added only to replace water loss from absorption by
plants, evaporation into the air from surface water, and removal of biomass such as
settled solid wastes from the system. As a result, aquaponics uses approximately
2% of the water that a conventionally irrigated farm requires for the same vegetable
production. This allows for aquaponic production of both crops and fish in areas
where water or fertile land is scarce.

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