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1999 Archives

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 Kavalos Lagoons.

"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
Leeds, United Kingdom, LS2 9JT