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FISH FARMING TECHNOLOGYTHE USE OF FEED IN RECIRCULATING AQUACULTURE SYSTEMS (RAS)
In 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
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
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.
Unlikeflow-throughor 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 thefiltrationsystems
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
RASprofitable
52 | May | June 2016 - International Aquafeed
Visit www.aquacultureuk.com for more informationor contact [email protected]
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