Recirculation systems are growing in importance for the aquaculture industry due to limited or expensive new water supplies or effluent disposal and higher risk of introducing pathogens from outside.
Closed circuits need biofilters to keep water clean. Biofilters contain Nitrosomonas and Nitrobacter bacteria which convert organic waste (in the form of amines) into nitrates, an analogous process to what happens in nature.
In a river, the concentration of these naturally present and useful bacteria is in balance with the concentration of ammonia/amine producing life such as fish.
In a farm, the concentration of fish is very high so the same effect can only be achieved by placing a very high concentration of amine-converting bacteria – which is the role of a biofilter.
Fish producers can contemplate quite different disinfection protocols in such systems and are faced with the question of whether their usual disinfectant could be harmful to the useful bacteria in the biofilters.
Several studies have concluded that Halamid® - at normal recommended dosages for the effective treatment of water in recirculation systems – is safely compatible with biofilters and causes no detrimental effect to their functioning.
Notably Boardman et al (2009)* showed in a series of controlled tests that a biofilter’s activity (measured by the rate of nitrate formation) in recirculated water with 20ppm Halamid® is not affected compared to filtering water with no disinfectant.
In systems with multiple tanks running through a single biofilter, Axcentive still recommends flushing only one tank at a time with Halamid® through the filter to maintain the level even lower than 20ppm.
Further information and guidelines for use can be obtained from local Halamid distributors or www.axcentive.com.
TEL: +33 4 42694090
*Responses of Nitrifying Bacteria to Aquaculture Chemotherapeutic Agents (Amy Kathleen Cheatham), January 27, 2009, Blacksburg, Virginia.
Dr. Gregory D. Boardman, Dr. Steven R. Craig., Dr. George J. Flick, Jr., Dr. Nancy G. Love