This document discusses recirculating aquaculture systems (RAS) for fish farming. RAS aim to provide more sustainable fish farming by reusing water in a closed loop system. The document defines RAS as systems that reuse at least 90% of water volume through treatment before recirculation. It also discusses the treatment processes involved to maintain water quality, including mechanical and biological filtration. RAS allow fish to be farmed anywhere and provide controls over environmental factors. However, they require large initial investments and have high operating costs but can be more sustainable and profitable than traditional aquaculture if designed properly.

1. FISH FARMING
TECHNOLOGY
SUPPLEMENT
Innovation and
service to the global
aquaculture sector
Defining RAS
safeguarding the future of the industry
SUPPLEMENT
Fusion Marine

2. W
ith concerns being raised about the impacts and
safety of open water cage and pond farming, the
spotlight has begun to fall upon more sustainable
and environmentally friendly methods for raising
fish. Recirculating Aquaculture Systems (RAS), provide clean,
sustainable and environmentally friendly products due to their closed
nature, high degree of control and detachment from the surrounding
environment. In order to assist the industry to develop and create
its own identity, it is necessary to properly define the technology
and the production methods. This is necessary in order to ensure
that the integrity of the industry and the sustainability claims of
RAS are safeguarded and not undermined by systems with different
environmental, economical, quality and welfare limits. Engineers
and biologists have been working hard for the past 20 years, and
continue to do so, in order to improve and optimise the design and
operations of such systems, in turn making them more profitable
and more popular as a method for large scale production of high
quality fish.
What is RAS?
A RAS usually consists of different compartmentalised units where the
waste water from the fish tanks is treated biologically and mechanically,
allowing it to be reused and maintained within the optimum ranges for
the species grown. As the name suggests, the water in such systems
circulates in a loop with minimum discharge, and a RAS can be defined
as such if the water exchange is limited to 15 or even 10 percent of
the total volume per day. In order to achieve such low exchange rates
(compared to flow through and partial exchange water systems, where
the exchange rate is much higher) the water treatment systems must
be correctly designed and sized so as to effectively deal with the waste
produced. A system where the treatment processes, for purposes of
economy, practicality or something else, are not sized to be able to
fully process the waste produced, and therefore have exchange rates
of anything above 10 to 15 percent, should therefore be considered
partial reuse.
Secondly, the circulation of the water is crucial to the definition –
while some extensive static ponds may have close to zero discharge,
the water is not circulated and therefore cannot be termed as RAS.
The reason for this defining and demarcation is to be able to help to
protect the quality of the industry and improve confidence in the sec-
tor. Chris Clayburn, Director of the RAS design and engineering com-
pany Aqua EcoSystems says: ‘It would eliminate those systems being
classified as RAS that are not and that may be "white elephants" for the
rest of us who understand the difference and the distinct advantages,
the complex work and considerable experience involved in developing
RAS and help clients/customers/investors to discriminate and invest in
viable operations’.
Crucial to the effective running of any RAS are the treatment pro-
cesses employed, such as mechanical filtration and biofiltration, while
effective denitrification, degassing, aeration, pH control are also essen-
tial in ensuring the optimal functioning of the system and maintaining
excellent fish health. Several technologies are available to remove
solids originating from fish waste or uneaten feed including: drum filters,
belt filters, parabolic filters, sand filters, and bead filters among others.
The selection of the proper mechanical filtration system during the
design phase of RAS is the first step to ensuring a system functions as
planned, with the main parameters of interest being particle sizes, solids
loading and water flows. The next stage in efficient water treatment
is nitrification of ammonia, produced as a by-product of the animals’
metabolism. Bacteria living in the biofilter oxidise ammonia to nitrite
followed by a second oxidation of nitrite to nitrate. While ammonia
and nitrite are highly toxic to fish and could be lethal if allowed to
build up in the water, nitrate can be tolerated in higher concentrations
before welfare of the fish becomes compromised.
In terms of the biofilter design, again there are many possi-
bilities including moving bed bioreactors, trickle filters, submerged and
upwelling bioreactors, and again different types of biofilter are more
Defining RAS
safeguarding the future of the industry
by Ivan Tankovski, Research Consultant, Pontus Aqua Ltd
and Dr Jack M James, Principal Consultant, Pontus Aqua; Director, Pontus Research Ltd
002 | INTERNATIONAL AQUAFEED | Fish farming Technology
FISH FARMING TECHNOLOGY

3. suited to different types of system and should be properly sized and
designed. While nitrate has low toxicity, chronically high levels can
retard the growth of the animals, reducing production potential, and is
one of the main reasons for water exchange in RAS.
Recently, denitrification reactors have been designed to facilitate the
removal of nitrate from RAS, thus minimising water exchange or facili-
tating the reduction in water exchange rates. Other factors which will
affect the exchange rate are dissolved gas build up, which in the case
of carbon dioxide can cause low oxygen absorption even under high
oxygen conditions, and nitrogen which can lead to gas bubble disease.
It is therefore essential to design a suitable degassing system into a RAS
to prevent these issues. In reducing the loading of very fine solids in
the system, technology such as protein skimming or foam fractionation
is utilised, which can assist in particle bound phosphorus removal and
reduction in ammonia due to removal of organics.
Finally, the use of effective systems to monitor and control param-
eters such as oxygen concentration, temperature, pH, water flows and
levels can also prove to be key to running a successful RAS as it allows
the farmer to be aware of all essential parameters at all times, and to
react quickly should a problem arise. Adoption of any of the design
factors mentioned will depend on a range of prevailing environmental
and economic factors, such as cost/benefit of technologies, location of
the operation, cultured species, water availability, local discharge regula-
tions and environmental conditions, among others.
Why use RAS technology at all?
RAS provides a unique opportunity to grow fish practically anywhere
and provides a great opportunity to expand aquaculture into areas
where it might previously have been impossible, thereby getting
produce physically closer to markets, reducing food miles and carbon
footprints. All environmental parameters can be monitored and strictly
controlled: temperature, oxygen saturation, pH, CO2 concentration,
suspended solids and photoperiod, allowing the commercial produc-
tion of virtually any species regardless of environmental preferences,
even in geographical locations which normally would be wholly unsuit-
able for a certain species. For example The Fresh Shrimp Company
produces tropical shrimp in England while the Abu Dhabi company
Asmak produces cold water salmon in their 500,000 square metre
onshore site.
The main benefits of RAS farming are:
• Feeding is constantly observed and can be controlled by robots
so that overfeeding is easily avoided. Feed conversion in RAS is
therefore much higher compared to other systems, reducing the
amount of feed necessary to grow the fish to market size, thus
reducing expenses and maximising profit.
• Growing fish in RAS allows the farmer to maintain uniformity in
his stock through size-grading and the adjustment of feeding rates.
• Exposure to disease is reduced as contact with the outside
environment is minimised through strict biosecurity protocols and
incoming water can be sourced from known clean sources or can
be treated before being introduced to the system. Additionally,
many RAS designs include the use of ultraviolet light and ozone
for water sterilisation. As well as ensuring high welfare standards,
this reduces the use of antibiotics and other pharmaceutical
products, highly undesirable in aquaculture when considering
environmental impacts of such chemicals, and the perception of
the consumer.
• Fish are not exposed to extreme weather conditions, and any
unusual behaviour can be recognised and reacted to accordingly,
and any dead fish can be promptly removed.
• Many concerns have been voiced over the mixing of wild
populations with fish escaping from nets in sea and lakes reducing
the genetic variability in nature, and this risk is removed in RAS
operations.
• Crucially, RAS allows the collection, treatment and potential uti-
lisation or treatment of waste products, including heat and CO2
as well as biological waste, reducing the impact of farming on the
environment. For example, with proper design waste heat energy
from equipment such as pumps or chillers can be harvested and
used to heat other parts of the farm or other operations.
Identifying the potential pitfalls, and avoiding them
As with any novel undertaking or technology, RAS can and does come
up against challenges. Chris Clayburn states that: ‘There will be some
genuine RAS that fail even when operating within certain defined limits,
which may be down to margins because RAS is an inherently expensive
way to produce fish [which] should be mitigated by thorough feasibility
study.’ Indeed research by CEFAS highlighted several cases of RAS
operation failings for a variety of reasons, including poor understanding
and planning, high costs, lower than expected sales values, poor design,
market challenges, environmental concerns and more.
Initially, building a RAS requires high capital investment and as such
must be well funded through the initial stages of growth through to
full production, which may be in the range of 12 to 18 months. This
can be off-putting to investors, but RAS must be seen as a long- term
investment, with potentially significant returns having. In addition to this,
high operational costs when using traditional energy sources can be a
barrier to development. However, through careful planning, proper
feasibility analysis and forward thinking, incorporating renewable energy
generation through solar, wind, gasification of waste or biomass genera-
tors and, in the case of exotic species in temperate climes, siting nearby
sources of waste heat such as power stations can make operations
significantly more viable. Even under standard energy conditions it is
possible to significantly reduce energy consumption through proper
design, bringing it in line with flow through systems. When considered
in tandem with reduced feed conversions, limited risks of stock failure,
reduced impact on local environment, the economic and environmen-
tal balance of RAS then become much more favourable.
In terms of the systems themselves, it is essential that the design
is fit-for-purpose for the very start, and as such each farm should be
treated as a unique project, ensuring all local variables are catered for.
Having a system with a poor or unsuitable design, or utilising a generic
system under special circumstances, could have disastrous consequenc-
es. Furthermore, an in depth knowledge of the target market and spe-
cies demand is also very important. It is not unheard of for farms to go
bankrupt because of poor market research. Once operational, several
factors must be considered for a system to be successful. One of them
is organic matter and nutrient loading in the effluent water, particularly
phosphorus and nitrogen which, if discharged, can contribute to the
eutrophication of the receiving water bodies. Therefore the design
must take account of this and have sufficient denitrification capabilities
to ensure discharges are as clean as possible, and at least comply with
local environmental guidelines.
While denitrification reactors can make operations economically
unfeasible, less intensive methods are becoming increasingly popu-
lar, such as stabilisation ponds and wetlands, which can also provide
additional income to the farmer. In addition to nitrate removal, the
removal or limitation of phosphorus discharge should also be con-
sidered such as optimising phosphorus retention in the fish, rapid
removal of solids from the water preventing phosphorous leaching
or dephosphonation techniques. Of course a farm will also produce
significant quantities of solid waste, which would need to be dealt
with. Firstly, it is important to treat this sludge and remove as much
water as possible through the use of dewatering belts, flocculation
tanks, or other available technologies, the resulting water entering
denitrification processes outlined above. The resulting dewatered
waste can then either be removed by municipal services, be used
in energy generation, or can be used as fertiliser or compost;
however, in this instance other regulations should be adhered to.
There are also biological methods for dealing with both dissolved
Fish farming Technology | INTERNATIONAL AQUAFEED | 003
FISH FARMING TECHNOLOGY

4. and solid waste, where the waste of one species is used as an input
for another.
For instance, aquaponics, itself in its commercial infancy, utilises dis-
solved waste products for growing plant crops, while Integrated Multi-
Trophic Aquaculture (IMTA) can utilise dissolved wastes in growing
algae, while solids can be utilised by detritivores or filter feeders, creat-
ing a balanced system with constant recycling
and utilisation of by-products and developing
multiple income streams.
Finally, technologies such as the up flow
sludge bed manure denitrification reactor
(USB-MDR) which allows for the reduction
of make-up water supply for nitrate con-
trol; reduction of nitrate-nitrogen discharge;
reduction of energy consumption due to a
low make up water supply flow and heat pro-
duction by the bacteria biomass in the USB-
MDR, concentration of the drum filter solids
flow; reduction of the size/volume of the
post treatment of the sludges and increased
alkalinity production and allows a pH neutral
fish culture operation, can provide the farmer
with the opportunity to reduce exchange
rates to just 0.15 percent in some cases.
The future of RAS
RAS is a set to become a very important
part of global aquaculture, just as long as the
potential pitfalls are avoided from the beginning
of the thought process – it can be considered
the ‘clean and green future of aquaculture’.
In improving the efficiency and reducing the
impact of RAS, research continues to seek to
optimise feeds to reduce waste production
and produce faeces with high water stability
and optimal particle sizes, facilitating the clean-
ing process. Additionally, new technologies
are being developed to optimise the nitrogen
removal from the systems.
One of them, ANNAMOX – a trademark
for an anaerobic ammonium oxidation process
owned by Paques - allows the direct conversion
of total ammonia nitrogen into nitrogen gas
under anaerobic conditions, helping to achieve
99 percent recycling in sea water systems.
Moreover, as highlighted previously, energy
reuse, optimising and developing energy saving
equipment and using alternative energy sources
are also helping in developing RAS into more
sustainable and environmental friendly practice,
governed by standards of best practice as well
as economical drivers. The state of the art as it
stands, coupled with the improvements which
are happening and will occur, will undoubtedly see RAS, with its defin-
ing 10 percent or less water exchange and circulated water, develop
considerably in the coming years.
www.pontusresearch.com
www.pontusaqua.com
References available on request
"With concerns being raised about the
impacts and safety of open water cage and
pond farming, the spotlight has begun to fall
upon more sustainable and environmentally
friendly methods for raising fish"
Does your company want to be involved in our
Fish Farming Technology supplement?
Contact Olivia Holden +44 1242 267706 - Email: oliviah@perendale.co.uk
004 | INTERNATIONAL AQUAFEED | Fish farming Technology
FISH FARMING TECHNOLOGY

5. Fish farming Technology | INTERNATIONAL AQUAFEED | 005
FISH FARMING TECHNOLOGY
Complete Plants and Machines
for the Production of Fish Feed
Contrary to conventional extruders, the KAHL extruder OEE is equipped
with a hydraulically adjustable die.
AMANDUS KAHL GmbH & Co. KG · Dieselstrasse 5-9 · D-21465 Reinbek / Hamburg · Phone: +49 40 727 71 0
info@akahl.de · www.akahl.de
See us at:
VIV Asia 2015
Stand H104.B039
Edición Española
www.aquafeed.co.uk
Subscribe at:
Or contact our circulation manager, Tuti Tan on:
+44 1242 267700 • Email:tutit@aquafeed.co.uk
Special Chinese langauge editions
中文专刊
Your FREE copy of the
Directory - woth £85One year subscription only £69 / €84 / US$114
Animal co-product
hydrolysates:
– a source of key molecules in aquaculture
feeds
Prevalence of mycotoxins in
aquafeed ingredients:
– an update
VOLUME 16 ISSUE 6 2013 - NOVEMBER | DECEMBER
INCORPORATING
FISH FARMING TECHNOLOGY
New functional
fish feeds to reduce
cardiovascular disease
Pellet distribution modelling:
– a tool for improved feed delivery in sea cages
IAF13.06.indd 1 22/11/2013 14:38
The potential of
microalgae meals
– in compound feeds for aquaculture
Understanding ammonia
in aquaculture ponds
VOLUME 16 ISSUE 5 2013 - SEPTEMBER | OCTOBER
INCORPORATING
FISH FARMING TECHNOLOGY
EXPERT TOPIC
– Salmon
AquaNor event review
IAF13.05.indd 1 13/09/2013 09:24
Maintaining ingredient
quality in extruded feeds
Fine particle filtration in
aquaculture
Effect of probiotic,
Hydroyeast Aquaculture
– as growth promoter for adult Nile tilapia
VO LU ME 16 IS S U E 4 2013 - JU LY | A U G U S T
IN C OR POR ATIN G
F ISH FAR MIN G TEC HN OLOGY
EXPERT TOPIC
– channel catfish
IAF13.04.indd 1 24/07/2013 14:33
They are what they eat
Enhancing the nutritional value of live feeds
with microalgae
Controlling mycotoxins with
binders
Ultraviolet
water disinfection for fish
farms and hatcheries
Niacin
– one of the key B vitamins for sustaining
healthy fish growth and production
VO LU ME 16 IS S U E 3 2013 - MAY | JU N E
IN C OR POR ATIN G
F ISH FAR MIN G TEC HN OLOGY
IAF13.03.indd 1 13/05/2013 16:03
Transforming aquaculture
production using
oxygenation systems
Nutritional benefits of
processed animal proteins
– in European aquafeeds
Towards aquafeeds with
increased food security
Bioenergetics
– application in aquaculture nutrition
VO LU ME 16 IS S U E 2 2013 - MA R CH | A PR IL
IN C OR POR ATIN G
F ISH FAR MIN G TEC HN OLOGY
IAF13.02.indd 1 04/04/2013 16:17
Chicken viscera for fish
feed formulation
Profitable aquafeed
moisture control
The shrimp feed industry in China
– an overview
Spray-dried plasma
– from porcine blood in diets for Atlantic
salmon parrs
VO LU ME 16 IS S U E 1 2013 - JA N UA RY | F E BR UA RY
IN C OR POR ATIN G
F ISH FAR MIN G TEC HN OLOGY
IAF13.01.indd 1 23/01/2013 10:51
+
Choose your language
Englishlanguage

6. F
usion Marine Ltd is a leading supplier of equipment for the
aquaculture sector, with a particular focus on robust and
versatile fish farm pens manufactured from tough poly-
ethylene and available in a variety of different formats and
specifications. The company’s range of fish farm pens have been
successfully installed in some of the harshest marine environments
in the world and are suitable for a wide range of species including
salmon, bream, bass, tuna, trout and many others.
With almost 25 years’ experience within the aquaculture sector,
Fusion Marine has forged strong relationships with customers based
on a reputation for service and support, combined with excellent
product quality. For example, the company works closely with cus-
tomers to ‘future-proof’ their fish farm operations by providing new
equipment and upgrading existing infrastructure.
This upgrade and refurbishment work is proving particular popular
among aquaculture companies and provides an environmentally
friendly solution by using the material from old pens to manufacture
new systems incorporating the latest designs and technologies.
Fusion Marine is continually investing in new technology to ensure
it stays ahead of the field. Their expertise in plastics technology
has enabled the diversification of its product and service range to
include pontoons and support expertise for hatchery installations and
upgrades.
Fish pen overview
Fusion Marine circular fish pens are renowned around the work
for their toughness, versatility and overall excellence of design.
Manufactured from tough polyethylene (PE), cutting-edge technol-
ogy is used in their manufacture to ensure the highest quality and
most modern equipment. Available in two or three-ring formats,
innovative Electrofusion and butt-fusion jointing techniques are
utilised in the manufacturing processes to ensure optimum strength
and integrity.
Fusion Marine
Innovation and
service to the global
aquaculture sector
006 | INTERNATIONAL AQUAFEED | Fish farming Technology
FISH FARMING TECHNOLOGY

7. Recently, Fusion Marine teamed up with PE jointing specialist
ControlPoint to utilise its suite of technologies, enabling Fusion
engineers to be supported by two new advanced information and
inspection systems. The adoption of these advanced technologies is
an integral part of Fusion Marine’s commitment to deliver the best
possible customer service by continually innovating and enhancing its
manufacture and installation standards.
Aquaflex pens
The proven and highly successful Aquaflex aquaculture system
covers fish farming pen sizes from 35-80m circumference and utilises
250mm diameter flotation pipes. Incredibly robust and featuring a
modular design, Aquaflex fish farm pens have been engineered to give
fish farmers peace of mind so they can concentrate on rearing quality
farmed fish. Aquaflex is the ideal fish farming system for inshore sea
farms, fresh water fish farms, pilot fish farms and for rearing juvenile
fish stock.
Oceanflex pens
Oceanflex is the fish farm pen of choice for aquaculture com-
panies operating over a wide variety of marine sites. These heavy
duty, all polyethylene fish farm pens are built on the security and
safety of Fusion Marine’s proven three ring flotation fish farm
system. The Oceanflex aquaculture system is used around the
world for a large range of marine species. This versatile system
features 315mm diameter flotation pipes for pen sizes ranging
from 60-150m.
Triton pens
The Triton 400 and 450 fish pens have been developed to meet
the demanding conditions found in open sea fish farming sites.
With the future trend of fish farming moving further offshore, these
incredibly strong large diameter aquaculture pens provide the perfect
solution.
Triton is the fish farm pen of the future, with its incredible strength
Fish farming Technology | INTERNATIONAL AQUAFEED | 007
FISH FARMING TECHNOLOGY

8. combined with large diameter making it ideal for exposed offshore
locations. The extra -large three-ring Triton 450 cage has already
proved extremely successful for the offshore farming of tuna and
salmon. The new Triton 400 version has been developed to provide
an alternative specification that can be used in either three or two ring
formats.
The excellent buoyancy and strength of the Triton range provides
a safe and stable working platform aided by heavy gauge handrails. All
Triton cages feature anti-slip safety decking, with the handrails and all
other fittings constructed from tough and corrosion resistant PE.
Square pens
Ideal for freshwater and estuarine locations, these pens are excel-
lent for small-scale production and the rearing of juveniles. Widely
used around the world, they are manufactured to individual customer
specifications.
Hatcheries
Fusion Marine’s expertise with plastic piping and associated equip-
ment, coupled with their strong track record in the aquaculture market
enables the highest level of support for hatchery operations.
The fabrication, supply and bespoke installation of pipes, manifolds,
valves, PE sheets and other specialised parts can be utilised in both
small and large-scale hatcheries. As well as supplying a full turnkey pack-
age from design and installation to after sales service, the company also
carry out repairs and alterations to existing systems. This expertise can
be applied to other operations that utilise pipe-work and associated
fittings such as shellfish depuration units.
Pontoons
Fusion Marine pontoons provide convenient and cost effective
access for a variety of waterside locations, including remote coastal
areas.
Constructed from tough polyethylene and recycled plastic, the flex-
ible nature of these custom-sized pontoons enables them to be sited
on shelving beaches and other similar areas. As the tide or water level
fluctuates, the pontoon follows the contours of the foreshore, provid-
ing the perfect answer for individuals, businesses and other organisa-
tions looking to gain easy access to the sea or other waterbody.
These low maintenance pontoons are ideal for the landing and
mooring of small and medium sized vessels. There is the option
to increase the available berthing space by utilising a hammerhead
arrangement at the end. All pontoons are specifically designed in close
consultation with the customer to ensure they meet their specific site
and size requirements.
For specific aquaculture applications, pontoons are manufactured as
landing and service platforms for fish farms, for example as a central
pontoon with fish pens arranged on either side. Fish transfer pontoons
are also designed and manufactured, enabling wellboats to pump fish
ashore, or take fish onboard.
www.fusionmarine.com
008 | INTERNATIONAL AQUAFEED | Fish farming Technology
FISH FARMING TECHNOLOGY