Aquaculture Recirculation Systems

Bes­i­des tra­di­tio­nal aquacul­tu­ral cul­ti­va­ti­on methods like pond cul­tu­re, net cages and race­ways, the clo­sed sys­tem cal­led recir­cu­la­ting aquacul­tu­re sys­tem (abbr. RAS) has been estab­lished more and more during the last deca­des. This is the most modern and abo­ve all the most effi­ci­ent opti­on of all fish farms. Recir­cu­la­ti­on sys­tems by defi­ni­ti­on have a dai­ly water exch­an­ge rate below 10% of the who­le water volu­me of the faci­li­ty (EIFAC, 1986). Sus­tainable and ele­va­ted tech­no­lo­gi­cal cir­cu­la­ti­on sys­tems, like­wi­se the SEAWATER Cube, can even achie­ve a dai­ly water exch­an­ge rate below 1% and are the­r­e­fo­re espe­ci­al­ly resour­ce-con­ser­ving. Uni­que fea­tures of this cul­ti­va­ti­on form are the com­ple­te inde­pen­dence of loca­ti­on, becau­se the­re is no natu­ral water­bo­dy nee­ded, as well as the sepa­ra­ti­on from the envi­ron­ment. Through a con­ti­nuous water tre­at­ment using phy­si­cal and bio­lo­gi­cal fil­ter sys­tems within the recir­cu­la­ti­on, a gre­at water qua­li­ty is achie­ved. Fur­ther­mo­re, the sepa­ra­ti­on per­mits to avo­id inter­ac­tions with the envi­ron­ment and to save resour­ces. Such extre­me meteo­ro­lo­gi­cal and hydro­lo­gi­cal occur­ren­ces (e. g. storms, waves or brea­k­ers), indus­tri­al risks (oil pol­lu­ti­on, nuclear acci­dents) or bio­ge­nic hazards (toxic algal blooms) are con­side­red no direct dan­gers for a RAS.

Other advan­ta­ges are:

• con­su­mer protection
• food safe­ty
• relia­bi­li­ty of the pro­duc­tion process
• expan­ded portfolio
• sus­taina­bi­li­ty

Due the on the ani­mal wel­fa­re adapt­ed water para­me­ters as well as their con­stant con­trol, hig­her sto­cking den­si­ties than in e. g. the con­ven­tio­nal pond cul­tu­re are attainable, wit­hout expo­sing the ani­mals to unneces­sa­ry stress. The result is a con­sider­a­b­ly grea­ter space effi­ci­en­cy and that is why a modern recir­cu­la­ti­on sys­tem only takes up around 1% of the area of a pond sys­tem, while pro­du­cing the same annu­al amount.

A spe­cial kind of aquacul­tu­re in recir­cu­la­ting sys­tems is aqua­po­nics. It is a com­bi­na­ti­on of aquacul­tu­re and hydro­po­nics (crop gro­wing wit­hout soil). With this inte­gra­ti­on, not only the water cycle is clo­sed but also the nut­ri­ent cycle, becau­se the water out­let of the fish farm is led into the plant patches. Crops like toma­toes, basil or egg­plants are stan­ding in an inor­ga­nic bed­rock such as gra­vel or clay gra­nu­la­te and are extra­c­ting the nut­ri­ents from the freshwa­ter. Under the­se con­di­ti­ons, the growth of plants is excel­lent, and they can fil­tra­te the water up to this point, whe­re the water can be led back into the fish tank wit­hout having to tre­at it any further.