A Minimal Water Exchange Aquaculture System, also known as a Recirculating Aquaculture System (RAS), is a modern and sustainable approach to fish farming that minimizes water usage by continuously recycling and treating the water within a closed system. In this system, water is reused and treated to maintain optimal water quality for fish while reducing the environmental impact associated with traditional aquaculture methods. The key components of a minimal water exchange aquaculture system include: 1. Fish Tanks: These are the primary units where fish are raised. The tanks are designed to provide suitable conditions for fish growth, such as appropriate water depth, temperature, and oxygen levels. 2. Filtration System: RAS incorporates various filtration components to remove solid waste, excess nutrients, and harmful substances from the water. Mechanical filters remove large particles, while biological filters foster beneficial bacteria that convert toxic ammonia into less harmful substances. 3. Water Treatment: Water treatment technologies, such as UV sterilization or ozonation, are used to control pathogens and maintain water quality within acceptable parameters. These methods help to ensure a healthy environment for the fish. 4. Oxygenation: Adequate oxygen levels are critical for fish health. RAS employs techniques such as aerators, oxygen injectors, or oxygen cones to maintain dissolved oxygen levels throughout the system. 5. Monitoring and Control: RAS relies on advanced monitoring and control systems to continuously measure and regulate parameters such as temperature, pH, oxygen levels, and water flow. This ensures optimal conditions for fish growth and allows for timely adjustments if any deviations occur. The benefits of a Minimal Water Exchange Aquaculture System (RAS) include: 1. Water Conservation: RAS significantly reduces water consumption by recycling and reusing water within the system. It helps conserve this valuable resource and minimizes the environmental impact associated with traditional aquaculture, which often requires large amounts of freshwater usage. 2. Improved Water Quality: The water in a RAS undergoes thorough filtration and treatment, resulting in high-quality water conditions for the fish. By removing waste and controlling water parameters, RAS helps minimize the risk of disease outbreaks and promotes optimal fish health. 3. Reduced Environmental Impact: The closed-loop nature of RAS prevents the release of excess nutrients and waste into the surrounding environment, minimizing the impact on natural ecosystems and reducing the risk of pollution. 4. Increased Production Density: RAS allows for higher stocking densities compared to traditional aquaculture systems. The controlled environment and efficient waste management of RAS enable farmers to maximize production within a smaller footprint. 5. Disease Control: The controlled and isolated environment of RAS helps minimize the risk of disease transmission

1. MINIMAL WATER EXCHANGE AQUACULTURE
SYSTEM
(Recirculating Aquaculture System)
Vishal Solanki

2. Introduction
• In farm, water use in aquaculture can be up to 45 cubic meters per Kg produced in ponds
• Minimal exchange, intensive culture system requires little, if any, water exchange and has high animal
stocking densities so that, it is crucial to maintain water quality in tolerance range for aquatic animal
growth
• water is reused, the water volume requirement in RAS is only about 20% of what conventional open pond
culture demands
• The bio floc keeps microbial diseases away
• zero-water exchange makes it eco-friendly
• Recirculatory aquaculture systems are used where water exchange is limited but comparatively more
capital intensive

3. Potential
Climate
Market
and trade
Rivers and
Canals –
1.95 lakh
km
Reservoirs
– 31.5 lakh
ha
Tanks And
Ponds -
24.1 lakh
ha
Floodplain
lakes –
8.12 lakh
ha
Marine
NATURAL
RESOURCE

5. Problems
Urbanization
Water Quality
Antibiotic
Sensitivity
• When stocking density
high, the build-up of
nitrogenous wastes like
ammonia, requires the
producer to implement
measures to manage it
properly (Nair et al.,
2020).

6. Zero water discharge
• Low/no water discharge
• Improved system from batch system
• Emphasize in microbial manipulation
• Nitrogen toxic compound removal by microbial loop system
• Microbial consortia added regularly to the system
• Microbial component is kept dominant in the system
• Need additional compartment for separated microbial cultivation

7. Biofloc
• Low/no water discharge
• Improved system from batch system
• Add carbon source to enhance heterotrophic bacteria consortium
• Emphasize in C/N ratio in the system
• ‘waste’ Nitrogen is converted to high concentration of total
suspended solid (microbial biomass) that can act as highly
protein feed for cultured animal
• Consider well mixing and aeration to compensate BOD in the
system

9. Why Recirculating
Aquaculture?
• Scarcity of good quality water for aquaculture
• Land is expensive, especially near good areas with plenty of water
• Greater control over effluents and treatment
• Permits the culture of aquatic organisms outside of natural range
• RAS offer a high degree of fish environmental control (Summerfelt, 1996)

10. History of RAS
• The earliest scientific research on RAS conducted in Japan in the 1950s
focused on biofilter design for carp production driven by the need to use
locally limited water resources more productively (Murray et al.,2014).
• Later Europe and the United States scientist adapted technology
• Early efforts included primarily work on marine systems for fish and
crustacean production
• Soon adopted in arid regions where the agriculture sector is restricted by
water supply
• The trust in technology was reinforced by the successful operation of public
as well as domestic aquaria, which generally feature over-sized treatment
units to ensure crystal-clear water (Espinal et al., 2019)

11. What is RAS?
• Recirculating aquaculture system (RAS) is a production system in which
a certain volume of culture water is reused through continuous treatment
(Dalsgaard et al., 2017)
• This system is adopted for an intensive aquaculture system where
aquatic species are reared in high stocking density and fed with a
formulated diet along with a provision for constant aeration (Dalsgaard
et al., 2017)
• RAS require less than 10% of the water and much less land than do
extensive pond systems to produce a given quantity of fish, and RAS
technology reduces the effluent volume (Timmons et al., 2002)

12. Design of RAS
According to
Parker (2011)
RAS design:
Solids filter Biological filter Tanks Aeration Disinfection Heaters/chillers Lighting
• Depending on the water temperature and fish species selected, a water
heating system may be necessary. Ozone and ultraviolet sterilization
also may be advantageous to reduce organic and bacteria loads
(Helfrich & Libey, 1991).

13. Process of Recirculating Aquaculture System
Degasser
Mechanical filter
Trickling filter
Fish tank
UV disinfection Oxygen enrichment
Biological filter

16. Holding/culture tanks
• These provide space for the fish
to be held in a range of shapes,
sizes and construction methods
are used
• Generally round tank used
– self-cleaning
Source: Agrifarming

17. Mechanical filter
• Waste Solids removal
• Settleable, Suspended, Floatable,
Dissolved solids
• Types of solids filters used are:
– Settlement or sedimentation systems
(large scale, pond systems),
– Mechanical filtration (screen
filtration or granular media
filtration),
– Chemical adsorption (activated
carbon, protein skimmer, foam
fractionation) Source: aquacultureida

18. Mechanical filter
• Larger pond or recirculating
systems may use more than one
method of filtration to remove
solids from a system
• eg. screen filters may be used to
pre-filter water before passing
through a sand filter
• Whatever filter system used
must be washed regularly to
remove the debris Drum filter
Image source: Google image

19. Biological filter
• A biological filter (biofilter) relies on bacteria to convert ammonia into
nitrate via a two step process called nitrification
• The biofilter provides a substrate (gravel, bioballs, sponge etc.) for
bacteria to colonise and contact with the water to be processed
– larger surface area = larger bacterial population = greater the
nitrification capacity = better water quality & healthy fish
• Common and effective filters for the management of ammonia and
nitrite include Submerged filters, Trickle filters, and fluidized bed sand
filters (Sastry et al., 1999)

20. Nitrification
• Nitrification is performed by two
groups of aerobic bacteria in a two
stage process:
– Nitrosomonas spp. (NH3 TO NO2)
– Nitrobacter spp. and Nitrospira
spp.(NO2to NO3)
• The nitrification As the process is
aerobic, oxygen and continual
water movement is essential
• Use of algal scrubbers can be
incorporated to remove nitrate
(Adey and Loveland, 1998)
Source: Linbo, 2009

21. Types of Biofilters
Source: biofilters
Trickle
Submerged

22. Continue
Fluidised bed
Source: sandfiltergakanko

23. Sump/reservoir
• This increases the volume of water in the system –generally point where
water is exchanged
• Can be used to facilitate water quality control and acts as a collection
point for the pump to recirculate water

24. Pump
• Some form of pump is needed to recirculate the water through the culture system
• Centrifugal pump used to most modern RAS designs target recirculating pressure of
about 10 feet (3 m).
• Airlift pumps are capable of moving large volumes of water at extremely low lifts.
Large diameter air-lifts (>8 inches or 20 cm) have recirculation capabilities of
several hundred gallons per minute (2,000 to 3,000 lpm), with lifts <18 inches (46
cm) (Malone, 2013).
Source: Google image

25. Aeration
• Recirculating systems should maintain adequate dissolved oxy-gen (DO)
concentrations of at least 6 mg/L and keep carbon dioxide (CO2) concentrations at
less than 25 mg/L for best fish growth (Colt and Watten, 1988; Boyd and Watten,
1989)
• Diffused aeration systems can transfer oxygen at an average rate of 1.3 kg O2/kW-h
(2.15 lbs./hp -hour) under standard (20oC, O mg/L DO, clean water) test conditions
(Colt and Tchobanoglous, 1979).
Colt and Watten, 1988

26. Additional equipment
• Spotte (1979) notes that the effectiveness of UV
sterilization depends upon the size of the organism, the
amount of UV radiation, and the level of penetration of
the radiation into the water. To be effective,
microorganisms must come in close proximity to the UV
radiation source (0.5 cm, 0.2 inches or less).
• Ozone treatment use as removal of solid matters,
bactericide, parasiticide and virucide (Gonçalves and
Gagnon, 2011) and The efficiency of the disinfecting
action depends upon the contact time and residual
concentration of O3 in the water with the
microorganisms (Summerfelt, 2003).
Source: Google image
Source: Google image

27. Large scale RAS
Source: NATI, 2011

28. Small scale RAS
Source: NATI, 2011

29. Water parameter in fish culture for RAS (Jacob
Bregnballe, 2015)

30. Stocking Densities
• Some species require specific facility
• Stocking density varies with life stage and species of fish. For example
Salmonids molt are stocked at 1-3kg/m3, grown out at 10-40kg/m3
(NATI, 2011).
• Stocking rates for ornamental are normally much lower 0.1 to 1kg/m3
but intensive systems can get to 3 kg/m3 (NATI, 2011).

31. Feeding
• A good quality artificial pellet is best for use in RAS to help maintain good
water quality
• Protein level is generally 40% or higher
• Pellets need some form of pigment
• Should have good vitamin levels (Vitamin B and C important)
• Supplemental feeding of live feed can help improve growth and
colour/quality of fish.
• Natural pigment blends such as capsicum extract (produces red colours) or
marigold extract (produces yellow/orange colours) can also be used. These
are mixed at 0.1 -0.5% into feeds (Britton, 1996).
• Good colouration is the key to production of high quality fish.

32. Pelleted Feeds
• Formulated diets: Pellets, powders
(crumbles) or emulsions (usually fed
to live food species to boost their
nutritional value for the culture
species) to match the mouth size of the
fish species;
• Floating, slow sinking, sinking;
• Soft pellets (mimic natural feeds) or
hard pellets.
Source: fish feed extruder

33. Stress and Disease
• Disease control is essential in RAS
• Stress and disease are inter-related,
control of these factors is important
for health of fish.
• Stress causes physiological changes
that compromise immunity and
leaves the fish more susceptible to
disease.
• Maintaining optimal conditions and
good hygiene is essential
Image source: Nippyfish

34. Disease Detection
• Routine disease diagnosis
• Parasites are easily diagnosed with a microscope
• Diagnosis of bacterial and viral would generally involve sending samples to a
laboratory
• Government surveillance
– Important to be involved
– health certificate

35. Facility Hygiene
• Ensure all equipment is cleaned and disinfected properly after use
• Avoid using equipment from other farms, unless properly cleaned
• Using separate equipment in different parts of the facility also reduces risk
• Footbaths and washing hands can reduce this risk

36. Waste management in RAS
• Due to the intensive mode of fish production in many of these
systems, waste treatment within the recirculating loop as well as in
the effluents of these systems is of primary concern
• In outdoor RAS, such treatment is often achieved within the
recirculating loop
• waste produced by the fish is captured and removed in a
concentrated effluent stream that may be treated onsite before final
discharge
• Outdoor RAS, mostly situated in warmer climates, are often
operated with partial waste reduction within the recirculation loop

37. Waste management in RAS
• In indoor systems, capture of solid waste and conversion of ammonia to
nitrate by nitrification are usually the main treatment steps within the
recirculating loop
• Effluent treatment may comprise devices for sludge thickening, sludge
digestion as well as those for inorganic phosphate and nitrogen removal
• Whereas waste disposed from freshwater RAS may be treated in
regional waste treatment facilities or may be used for agricultural
purposes in the form of fertilizer or compost

38. Backyard Recirculation
Aquaculture System
• Freshwater aquaculture in India started with the stocking of carp in
backyard ponds in West Bengal, Odisha and expanded to other states of
India (Rutaisire et al., 2017)
• However, to encourage small-scale fish farmers and entrepreneurs and
also to facilitate fish production in urban and peri-urban areas where
land and water are scarce, it is proposed to promote Backyard RAS

39. Design of Backyard Recirculation Aquaculture System
Image source: NFDB

40. Comparison between earthen pond and RAS
DOF

41. Cost of construction and management
Investment Budget 100% (Capital Costs)
Civil works: Land development, building,
concrete and construction, piping,
electrics, walkways
46%
Recirculation system: Design and
equipment, freight and installation
35%
Fish tanks 12%
Feed and light systems 2%
Heating, chilling, ventilation 2%
Fish handling incl. pipes 2%
Operational equipment 1%

42. Species suitable for RAS
• Baramundi/ Asian Seabass/Bhetki (Lates calcarifer)
• Cobia (Rachycentron canadum)
• Silver/Indian Pompano (Trichinotus Blochii/ Trichinotus mookalee)
• Tilapia (Oreochromis niloticus)
• Pearl spot/Karimeen (Etroplus suratensis)
• Pangasius (Pangasianodon hypophthalmus)
• Rainbow Trout (Oncorhynchus mykiss), especially in Hilly/cold water Region

44. Case study

45. Cont..
The ICAR-CMFRI has developed the technology for breeding and seed production of around fifteen varieties
of marine ornamental fishes such as clown fishes and damsel fishes. As brood stock development is an
important part of the breeding programme, more emphasis need to be given on this component to ensure
better larval survival and production of healthy larvae. The mini RAS (Recirculatory Aquaculture System)
developed for brood stock maintenance would be highly useful for a small scale marine ornamental fish
breeding and seed production unit

46. Cont..

47. Cont…

48. Advantages
• Fully controlled environment for the fish
• Low water use
• Efficient land use
• Optimal feeding strategy
• Easy grading and harvesting of fish
• Full disease control
• A boon for income generation in water deficient areas of India like
Rajasthan etc. (Sharma et al., 2018)
• To Generate employment

49. Conclusion
• Recirculating aquaculture system is the key to the future of
aquaculture.
• It makes sustainable use of the water resources, and in places
where there is scarcity of good quality water
• There is low pollution to the surroundings in recirculating
aquaculture systems
• Even with all the successes and improvements, though, it is
still challenging to implement and manage recirculation
systems that are cost competitive with other less capital-
intensive production strategies

50. References
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cascade aeration, and low-head or U-tube oxygen-ation. In: Libey, G.S., Timmons, M.B. (Eds.), Successes andFailures in Commercial Recirculating
Aquaculture. Proceedings ofan International Workshop. Roanoke, Virginia, pp. 217–244. July19–21, 1996
• Jacob Bregnballe, 2015. A Guide to Recirculation Aquaculture: An introduction to the new environmentally friendly and highly productive closed
fish farming systems. Published by FAO and EUROFISH International Organisation, 2015, pages 1-100
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velihood_Improvement/links/5b0f9d4da6fdcc80995bd1fe/Ornamental-Fishery-Resources-in-India-Diversified-Option-for-Livelihood-
Improvement.pdf
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athttp://www.hie.co.uk.
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51. • Nazar, A K A and Jayakumar, R and Anikuttan, K K (2019) Mini RAS (Recirculatory Aquaculture System) for broodstock maintenance in
Marine Ornamental fish hatcheries, CMFRI Booklet Series No. 13/2019. Technical Report. ICAR - Central Marine Fisheries Research
Institute, Kochi.
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