Recirculation in fish

Application of Recirculatory
System in Fish Culture
Presented By:- SHWETANSHUMALA

Introduction
 Recirculation aquaculture systems (RAS) flows from a fish
tank through a treatment process and is then returned to the
tank, hence the term recirculating aquaculture systems.
 RAS technology has steadily developed over the past 30 years
and is widely used for bloodstock management, in hatcheries
and increasingly for salmon production.
 Recirculating systems filter and clean the water for recycling
back through fish culture tanks.
 A filtering (biofilter) system is necessary to purify the water
and remove or detoxify harmful waste products and uneaten
feed.
 Recirculation systems also occupy very little area and require
little water consumption compared to other forms of
aquaculture.

Water
Fig-1 recirculating aquaculture system
Biological
filtration
Fish
Mechanical filtration
Water

Fig. Schematic of a recirculating aquaculture system consisting of
shrimp culture system and water treatment system.

 Recirculation systems are becoming increasingly popular as
they provide a predictable and constant environment for
growing fish. Species of fish that can be cultured within
recirculation systems include barramundi, Murray cod, Silver
perch, snapper and eels plus a number of other species.
 Recirculation systems occupy a very small area and allow the
grower to stock fish at high densities and produce high yields
per unit area.

Necessity of recirculation
 The Recirculatory system is necessary to reduce the risk of
disease/ parasite infections considerably.
 Oxygen can be replenished through aeration and most of the
carbon di-oxide is dissipated, the removal of metabolic
products especially ammonia involve more complex system.
 This system of farming highly improves survival and growth
performance of fish due to high degree of control over the
water quality.
 This system eliminates water quality problems.
 Recirculation of waste-loaded pond water reduces potential
pollutants which assures the availability of quality water for
fish farming where the source of fresh water is limited.

Application of recirculation
 The use of RAS technology is already increasing in the
Scottish salmon industry and further investment in this area
will almost certainly be essential for the successful future of
the industry.
 There is a long-term threat to the industry from RAS
technology being adopted closer to major markets, but this
should be seen as an incentive to continue to innovate for cost
competitiveness using the natural resources available in
Scotland.
 The first European RAS farmed salmon to be delivered to
market had a 20-30% higher production cost compared to the
most efficient cage farm in Norway.
 The USA, which relies almost entirely on imports to meet its
demand for salmon, also has one of the largest markets for
premium seafood products.

 China and SE Asia also represent important emergent
markets. Recent European salmon and sea bass RAS start-ups
are already targeting these markets and this is central to their
business plans.

Types of Recirculatory system
1. Zero-water exchange system
 Zero-water discharge , sludge removal
and fish culture. Each system includes
the three numbers of one hectare fish
grow-out pond, one hectare water
treatment pond for culture of fish and
bivalves.
 Cement cistern for sedimentation of
phytoplankton, a sludge-setting pond,
sludge-drying bed is removed from
grow-out ponds through the setting
pond.
 In this system, fish is stocked in each
pond at the rate varying between
8,000-10,000 /ha.

In-pond treatment system
 In this system, remove the excess
algae and suspended solids for
mussels.
 Four aerators are placed in such a
way that the pond water is
circulated and at the same time
waste materials are concentrated
at the centre of the culture pond.

Pond-in-pond Recirculatory
system
 This system consists of two ponds ,
the pond is utilized for intensive
culture and the second one is for
extensive farming.
 The intensive pond is somewhat
deeper than the extensive one and is
provided with paddle wheel aerators.
 Different species of fish such as
carps, fresh water prawn and bivalves
are stocked in extensive pond at
lower densities.

Drainage canal system
 In this system, fish farm is
circumscribed by a number of
canals. These canals and farm
ponds are filled up with water and
the water allowed to stand for three
months.
 Water of the drainage canal is then
circulated to the pond via the
supply canal. The canals are
provided with a number of aerators
for aeration of the water.
 Canals are also used as
sedimentation beds. Fish
production for this system about 8
tones/ha /carp.

Earthen pond system
 This is the most appropriate type of
west-water treatment for developing
countries. The system consist of a
series of ponds in which bacterial and
algal growth can occur in a symbiotic
manner.
 Bacteria utilize the organic matter from
which they produce inorganic nutrients
which are used by algae. Algae, in turn,
produce oxygen through
photosynthesis. This oxygen is
consumed by bacteria. This co-
existence of bacteria and algae for the
benefit of each other is termed as
symbiosis.

Recirculation Components
A recirculation fish farming system
comprises of a number of major
components that are necessary for
the management of the system. This
includes both site and system
components.
 Site Components
 Building
 Pump House
 Three Phase Electricity
 Emergency Generator
 Bulk Feed Storage
 Purging and Packaging Facilities

Recirculatory design
Growing tank
Sump of
particulate
removal device
Biofilter
Oxygen
injection with U-
tube aeration
Water
circulation
pump.

Growing tank
 Fish tanks typically are rectangular,
circular, or oval in shape.
 Rearing tanks range in size from
500 to 500,000 gallons capacity.
 Tanks can be constructed of plastic,
concrete, metal, wood, glass, rubber
and plastic sheeting, or any other
materials that will hold water, not
corrode, and are not toxic to fish.
Rectangular
tank
Round tank

Sump of particulate removal device
 A sump (clarifier tank) is used to prevent
the excessive accumulation of fish
excretory products and waste feed.
 Waste products increase the biological
oxygen demand (BOD), decrease the
dissolved oxygen content, lower the
carrying capacity (density of fish) that can
be reared, and may result in off-flavor in
fish products.

Biofilter
 The bacteria provide the waste
treatment by removing pollutants.
 The two primary water pollutants
that need to be removed are:-
 (a) fish waste (toxic ammonia
compounds) excreted into the
water
 (b) uneaten fish feed particles.
 The biofilter is the site where
beneficial bacteria remove
(detoxify) fish excretory products,
primarily ammonia.

Types of biofilter
• Submerged bed filters can have fixed
(immobile) media in which the water
flow can be upward, downward or
horizontally through the media.
• The fluidized bed reactor (FBR) is a
commonly used submerged bed filter
Submerged
bed filters
• trickling filter (TF)
• rotating biological contactors (RBC)
Emerged bed
filters

Other filters
Mechanical
• It physical separation of
concentration of
suspended particulate
matters from circulating
water.
Chemical
• In chemical filtration,
water is pumped through
a chemical media of
activated carbon, zeolite,
or other substances.

Oxygen injection with U-tube
aeration
 Effective diffusion of pure oxygen
gas into a liquid (water) can best be
accomplished using a U-tube
oxygenation, counter-current flow
injectors, or micro-bubble devices
(tubes or fine wet stones).
 The purpose is to dissolve much of
the oxygen injected so that it is
available to the fish, rather than
wasted by bubbling out of solution to
the atmosphere.

Water circulation pump.
 The rotating biological contractor (RBC) has a
water-wheel configuration consisting of plastic
media attached to a central axle which spins
slowly, moving the media through the water in
the RBC containment vessel.
 Advantages of the RBC are that it is self-aerating
and self-cleaning. Once established, it tends to
be very stable and can operate for years without
failure.

Advantages of Recirculation Systems
 Minimum demand on limited water resources. The limited
quantity of high quality water in aquifers and on the surface is
an indication that water recirculation systems will become
increasingly important as a means of meeting the demand for
fish.
 Minimum environmental impact. Recirculation systems
permit the concentration and removal of fish wastes so that
water pollution can be controlled and minimized.
 Few government permits are required. Because of limited
impact on environment, and limited withdrawal of waste
water, few permits are required for aquaculture systems based
on water recirculation.

 Closed circulation systems can be located near markets.
Suitable sites for other systems are dependent on location of
suitable water or land resources. Recirculation systems can be
located so that transportation costs and time between harvest
can be minimized.
 Water quality and temperature can be maximized. Water
temperature can be maintained at the optimum level for fast
growth and optimum feed conversion.
 Minimize losses from environmental hazards such as
predators, pollutants, and disease. Fish produced in closed
recirculation systems are safe from environmental pollutants
and many pathogens.
 Minimum space requirements for level of production. In
comparison to other types of systems, protein production in
closed systems require very little space.

Disadvantages of Recirculation Systems
 High Capital Costs. Capital costs of buildings, pumps, tanks,
heaters, etc. are higher than other systems of aquaculture.
 High Operating Costs. Closed systems require pumping water
though tanks and filters. The operating costs of pumps are
significant, and these costs may be the difference between
profitable and non profitable fish farms.
 Vulnerability to Mechanical Failure. Pumps make fish farm
vulnerable to breakdowns and blackouts which can result in
catastrophic losses of fish.
 Difficulties with Fish Health Management. Disease outbreaks,
once they occur, are difficult to manage. Pathogens in the
system find refuge in the biological filter and are difficult to
remove. Often the only option is to treat the fish in the tank,
thus killing the bacteria in the biofilter.

 Higher level of management is required. Unless managed
properly, sub-optimal conditions can occur that will result in
disease outbreaks and increased mortality. A much higher
level of system monitoring is required than in most other
systems.

Conclusion
 Recirculatory system indispensable for sustainable fish
culture and as a principle that forces to develop ecological
engineering design. This system creates greater efficiency and
productivity of ponds. The application of ecological
engineering principles to water pollution control in fish
culture ecosystems can reduce treatment costs. Fish culture
systems generate large volumes of nutrient-loaded water.
Since nutrient mass loading is the critical factor contributing
substantlly to ecosystem degradation, treatment of pond
water treatment is inevitable. Fish culture effluents are
difficult to treat becau se they contain relatively dilute
nutrients.
 The use of some ecological engineering principles permits
production of high-value fish crops while meeting stringent
nutrient/toxicant discharge regulations.

 The cost of water treatment can be reduced through use of a
less expensive technology and this technology will definitely
remove toxic metabolites to consistently less then toxic
concentrations without drastic reduction in fish productivity
or ecosystem quality.
Recirculatory system should be adopted in such a way that it
would facilitate some of the important criteria such as :-
 Effective removal of dissolved organic matter .
 Cost-effective removal of suspended solids.
 Removal of ammonia, methane, hydrogen sulfide and solid
wastes.
 High rate of water turn over.
 Adjustment of pH and feeding practices.
 Management of the culture system to avoid the risk of fish
kills in ponds.
 Adaptation of Recirculatory system will definitely transform
the abandoned fish farm into highly productive one.

References
 Epsilon Aquaculture Ltd. 2001. A Study of Low Cost Recirculation Aquaculture
(SR 485) –Final Report. Commissioned by the Sea fish Industry Authority.
 Good, C., Davidson, J., Welsh, C., Brazil, B., Snekvik, K. & Summerfelt, S.,
2009b. The impact of water exchange rate on the health and performance of
rainbow trout Oncorhynchus mykiss in water recirculation aquaculture.
 Guttman, L., & Rijn J. V. 2008. Identification of conditions underlying production
of geosmin and 2-methylisoborneol in a recirculating system. Aquaculture 279:85–
91.
 Guttman, L. & Rijn J. V., 2009. 2-Methylisoborneol and geosmin uptake by
organic sludge derived from a recirculating aquaculture system. Water Research
43: 474 – 480.
 Leonard, N., Guiraud, J.P., Gasset, E., Cailleres, J.P., Blancheton, J.P., 2002.
Bacteria and nutrients – nitrogen and carbon – in a recirculating system for sea
bass production. Aquacult. Eng. 26, 111–127.
 Staudenmann, J. Schonborn, A. and Etnier, C. 1996. Recycling the Resources.
Transtec publications, Switzerland. 543-557pp.
 Schrader, K.K., Davidson, J.W., Rimando, A.M. & Summerfelt, S.T., 2010.
Evaluation of ozonation on levels of the off-flavor compounds geosmin and 2-
methylisoborneol in water and rainbow trout Oncorhynchus mykiss from
recirculating aquaculture systems. Aquacultural Engineering 43: 46–50pp.

Recirculation in fish

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