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Panorama Archives: 2000
High Tech Fish Farming at Leeds
By Michael Boyd
Technology being developed by an international team led by British
researchers will enable fish to be farmed with a system that not only
secures conditions suitable to grow fish intensively in a tank but is
also friendly to the neighbouring environment.
The world-first project at Leeds University, northern England will,
it is claimed, eventually solve the serious waste-disposal problems
that beset all types of budding mariculture.
It is expected to be of especial value to the massive hatcheries set
up in the Far East. In the longer term the system will also enable
sea fish to be farmed at coastal locations in the desert and help
provide people living in barren regions with a vital source of
protein and a valuable, if unlikely, cash crop.
The intensive fish-growing system being developed is said to be
suitable for setting up anywhere in the world. Environmental
geo-chemist Dr Michael Krom is coordinating the 600,000 pounds
sterling FAIR programme funded by the European Commission that aims
to produce a working system within 18 months.
Growing marine fish in artificial environments is difficult because
the fish produce nitrogen-rich fish waste has to be constantly
removed. Bacteria bio-filters can do this effectively but the
cocktail of chemicals in sea water means that the bugs can also
produce gas which poisons the fish.
In essence the bacteria use oxygen to convert the ammonia excreted by
the fish into the water into nitrate in a process known as
nitrification. But in a closed system where the water is constantly
being recycled, it is inevitable that the nitrate will continue to
build up until it becomes a problem. Solving this problem by washing
the nitrate out of the system with replacement water would only
pollute the marine environment.
The Leeds system is modular in design. One unit holds the fish, the
next is a sedimentation tank to separate out the solid particles, and
the third contains the bacteria in a bio-filter. All of this layout
is quite conventional in aqua-culture. Where this project breaks new
ground is by adding for the first time a new de-nitrification module
where the nitrates are converted into nitrogen gas.
"This has been done in fresh water systems and we say that there is no
reason why it should not work in a marine application," said Dr Krom.
"The reason that nobody has yet tried it is very simple. If you get it
slightly wrong and use up all the nitrate, the bacteria will switch
their attention to sulphate and convert it into sulphide producing
the very toxic gas, hydrogen sulphide."
To avoid this happening Dr Krom's team is developing a transparent
cartridge containing red iron oxide which is chemically similar to
rust found on some metals. That achieves three things. It removes any
hydrogen sulphide from the water and as it does this the iron oxide
turns black warning the operator that something is amiss. Finally, it
also removes phosphate from the system. Also under consideration is
the addition of another process stage where ozone is added to
sterilise the water before it is recycled back into the first module
that contains the fish.
The team is in the middle of extensive laboratory trials to
understand quantitatively how each individual module works. Should
there be any unexpected behaviour they hope to isolate the unknown
factors before scaling up to a small-scale, pilot fish-farm system.
This is planned to be built in the Negev desert at Eilat, Israel, and
will be home for thousands of sea bream. This phase will be carried
out in conjunction with Dr Amir Neori at the National Marine Culture
Centre in Eilat. Also playing an important part at this stage will be
Dr Jaap van Rijn at the Hebrew University in Jerusalem who is an
expert in the operation of bio-filters in aqua-culture systems.
The computer modelling is in the hands of a father-and-son team of
Professor Henry Blackburn, a world expert on bacteria in the
environment, and Dr Nick Blackburn, an ecological modeller. Both are
from the University of Copenhagen in Elsinore.
The final scale-up before creating a commercial venture will take
place in Greece under Dr Antonis Kokkinakis at the Fisheries Research
Institute at Kavala, working with the Fisheries Association of
"What we are ultimately trying to do is create an international marine
agriculture in the same sense that we already have a mammal
agriculture,'' said Dr Krom. "Our present method of fishing from the sea
is playing havoc with the marine ecosystem. Not only are we
destroying the top predators but we are decimating the existing fish
stocks. This is why there has been a concerted move over the last 20
years to create a marine agriculture. We expect this project will be
a major contribution to this."
For information, contact:
Dr Michael Krom
School of Earth Sciences, Leeds University
United Kingdom, LS2 9JT
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