One of the greatest operating costs in aquaculture is the use of commercial feed pellets, which can comprise of up to 50-60 percent of total expense in some farms.

1. FISH FARMING TECHNOLOGY
THE USE OF FEED IN RECIRCULATING AQUACULTURE SYSTEMS (RAS)
I
n traditional forms of net-pen culture, the composition and wastage of these pellets is very
relevant to maintaining good growth of the species being grown, managing expenditure and
minimising environmental impacts on the surrounding water bodies. Ultimately, they do not
have a large effect overall on their operation as a system. In RAS however, these frequently
overlooked considerations, especially by new operators, are extremely important and their lack
of understanding can easily lead to the failure and loss of the facility’s economic viability.
As a commercial scale farm manager for several RAS farms over the years, I have seen and
overcome many of the problems associated with using commercial pellets formulated for net-
pen culture and the implications of overfeeding of these pellets on a filtration system. Unlike
flow- through or net-pen systems, any pellets that are not eaten by the cultured species are retained in the
system and must be processed by the RAS.
This is potentially a major problem as the filtration systems are designed to process faeces and not pellets,
which can be four times as dense. The leeching of oils from the pellets interferes with the foam fractionators
or protein skimmers in the systems that are responsible for removing micro-particulate organic material
from the water body, reducing the optimal water quality and clarity that must be maintained in order to
achieve the fast growth rates required to make a RAS profitable.
Another effect of uneaten pellets is the overloading on the mechanical filtration process
responsible for removing the macro-particulate organic material from the system, this
can cause the overflowing of these filters, which introduce these particles into the
bio-filter (often the next filtration process in the sequence in RAS), diminishing
its capacity to process the toxic inorganic compounds, such as ammonia,
released by the organisms being grown.
If the degree of overfeeding is frequent or severe, this bio-filtration
process provided by nitrifying bacteria (that take up to eight weeks to
establish), can be overcome by heterotrophic bacteria feeding on the
supply of organic material and cause a total failure of the system. The
outcome being that the toxic inorganic compounds, that are no longer
One of the greatest
operating costs in
aquaculture is the
use of commercial
feed pellets, which
can comprise of up
to 50-60 percent
of total expense
in some farms.
by Rob J Davies
– Aquabiotech
Group
50 | May | June 2016 - International Aquafeed

2. being filtered will build up in the RAS and
kill the cultured organisms within a matter of
days.
There are also several other factors that
are relevant to overfeeding in these systems
that effect the RAS farms’ operating costs
and efficiencies, apart from the obvious extra
expense of the wasted feed, also relevant for
net-pen and flow-through systems. Such as:
• Diminished oxygen injection transfer
efficiency, used to maintain optimal levels
for growth and health, especially during
handling and feeding events;
• Loss of appetite due to reduced water
quality and clarity, hence lower growth and
harvest sizes;
• An increase in vectors for pathogens or
parasites (in the form of available organic
particulate material);
• And the potential for unprocessed
antibacterial treatments (that may be used)
entering the bio-filter, which would also
kill the nitrifying bacteria, allowing for
the toxic inorganic materials to flourish
and risking the health of the cultured
organisms.
RAS farming is more complex than
traditional methods
As evident in these problems I have
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RAS farming is a
lot more complex
than the traditional
methods
and a lack of
appreciation of this
will mean that the
system is doomed
to fail, like so many
have before.
However, there are
strategies, solutions
and safeguards
that are currently
being developed
to minimise the
risk of these
problems from
occurring, such as
working with feed
manufacturers
to develop feeds
especially for RAS.
International Aquafeed - May | June 2016 | 51

3. FISH FARMING TECHNOLOGY
explained, that can occur from a simple matter of putting too much feed into a tank (or at too greater speed or
in too small of an area for the feeding rate of the organisms to cope with), RAS farming is a lot more complex
than the traditional methods and a lack of appreciation of this will mean that the system is doomed to fail, like
so many have before.
However, there are strategies, solutions and safeguards that are currently being developed to minimise the
risk of these problems from occurring, such as working with feed manufacturers to develop feeds especially for
RAS.
This includes altering the density of the pellet to maximise availability during tank turnover time; modifying
oil content and composition to reduce the effect of uneaten pellets on the micro- and macro-mechanical
filtration processes so that particulates are prevented from compromising the bio-filter; and the development of
technological by-passes, warning devices and innovative equipment and system design.
Maximising potential and economic viability
This is what we offer at AquaBioTech Group, using our knowledge, experience and innovation, taken from
the various different backgrounds of our consultants and the testing of our RAS equipment and development of
new ideas and system designs in our R&D Facility based in Malta.
The special training and after care service contract that we provide as standard to every one of our clients that
we build systems for ensures that the RAS’ we design and the feeding management strategies that we advise,
minimise the risk of such problems occurring, therefore maximising the potential and economic viability of the
farms and the future of sustainability of aquaculture in general.
Unlike flow- through
or net-pen systems,
any pellets that are
not eaten by the
cultured species
are retained in the
system and must be
processed by the
RAS. This is potentially
a major problem as
the filtration systems
are designed to
process faeces
and not pellets,
which can be four
times as dense.
The leeching of oils
from the pellets
interferes with the
foam fractionators
or protein skimmers
in the systems that
are responsible for
removing micro-
particulate organic
material from
the water body,
reducing the optimal
water quality and
clarity that must
be maintained in
order to achieve
the fast growth rates
required to make a
RAS profitable
52 | May | June 2016 - International Aquafeed

4. Visit www.aquacultureuk.com for more information
or contact info@aquacultureuk.com
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