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FISH FARMING TECHNOLOGY 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 control; reduction of nitrate-nitrogen discharge; reduction of energy consumption due to a low make up water supply flow and heat production by the bacteria biomass in the USBMDR, 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 cleaning 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 defining 10 percent or less water exchange and circulated water, develop considerably in the coming years.

"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" 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 dissolved waste products for growing plant crops, while Integrated MultiTrophic Aquaculture (IMTA) can utilise dissolved wastes in growing algae, while solids can be utilised by detritivores or filter feeders, creat-

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