Open Aquaculture Systems

The aquacul­tu­ral indus­try is chan­ging. One of the many rea­sons is the quick­ly incre­a­sing demand of fish. The per capi­ta con­sump­ti­on has dou­bled wit­hin the last five deca­des. Tra­di­tio­nal aquacul­tu­re from over 3000 years ago is not effi­ci­ent enough any­mo­re for pro­vi­ding the nowa­days around 8 bil­li­on humans with the nee­ded sup­ply. As a con­se­quence, various sys­tems have been deve­lo­ped or are still being deve­lo­ped to incre­a­se the effi­ci­en­cy: pond cul­tu­re, net cage cul­tu­re, race­ways (or also cal­led flow-through sys­tems) and clo­sed recir­cu­la­ting aquacul­tu­re sys­tems (abbr. RAS).

The pond cul­tu­re is the least tech­ni­cal exten­si­ve method; hence it is the world­wi­de most com­mon sys­tem. The­se pond sys­tems are often fami­ly busi­nes­ses but can also achie­ve grea­ter com­mer­cial sizes. In Euro­pe ponds are usual­ly built arti­fi­cial­ly and fea­ture a regu­la­ted water in- and out­let. The need of freshwa­ter is low com­pa­red to other sys­tems, becau­se the sto­cking den­si­ty in ponds is lower. Pond cul­ti­va­ti­on con­sists of natu­ral­ly occur­ring plants and ani­mals, which are not only kee­ping the water qua­li­ty up but also pro­vi­ding enough feed among one ano­t­her. This is cal­led an exten­si­ve form of cul­ti­va­ti­on. Fishes like carp, zan­der and pike are ide­al for pond cul­tu­re, due to the fact they get along with stan­ding water­bo­dies. If the­re is extra feed added, a hig­her water exchan­ge rate or acti­ve ven­ti­la­ti­on of the water for the requi­red oxy­gen sup­ply can beco­me necessary.

The net pen or net cage cul­tu­re is based in natu­ral waters and builds a well-defi­ned habi­tat wit­hin a pond, river or sea, whe­re the fish are being kept. Fee­ding, con­trol­ling and gathe­ring is easier com­pa­red to tra­di­tio­nal fishing through this defi­ned zone. Howe­ver, net cages are often ope­ra­ted inten­si­ve­ly and ther­eby a lot of ani­mals with high requi­re­ments of feed are kept in a con­cen­tra­ted domain. So net cages can have a gra­ve impact on the ambi­ent eco­sys­tem, becau­se une­a­ten feed as well as meta­bo­li­tes of the fish end up direct­ly in the sur­roun­dings. On one hand, the size of such net pens can vary from small sys­tems from 10 to 150 cubic meters of water, which are repre­sen­ta­ti­ve for Asia. On the other hand, sal­mon farms in Nor­way can have a water volu­me of up to 40,000 cubic meters. Com­mon mari­ne fishes for this kind of aquacul­tu­re sys­tem are seabream, codfi­sh, sal­mon, shark cat­fi­sh, tila­pia and seabass.

Race­ways are nume­rous tanks or chan­nels one after ano­t­her, which water is led through. That is the rea­son why the­se sys­tems are also cal­led “flow-through”. The tanks are con­struc­ted so that fish spe­ci­es, which are adap­ted to flowing water, can be held: e. g. trout, sea­bass or tila­pia. Con­di­tio­ned by the high fresh water inlet, the­se farms often have rela­tively high sto­cking den­si­ties and are the­re­fo­re inten­si­ve. From this fol­lows that gre­at loads of meta­bo­li­tes are lea­ving the sys­tem with the water out­let. Befo­re lea­ding this water back into natu­ral waters, it has to be pretrea­ted and the­re­fo­re makes this aquacul­tu­ral sys­tem com­pa­red to the­se abo­ve the most tech­ni­cal expensive.

The clo­sed recir­cu­la­ti­on sys­tem is the most tech­ni­cal­ly deman­ding aquacul­tu­re method of them all. The so-cal­led RAS (recir­cu­la­ting aquacul­tu­re sys­tem) is reu­sing the same water by uti­li­zing mecha­ni­cal and bio­lo­gi­cal fil­ters and tre­at­ment pro­ces­ses to obtain a con­ti­nuous­ly ide­al water qua­li­ty for the kept fish. It is the­re­with non­in­ter­ac­ting with the envi­ron­ment. Such high tech­ni­cal and ener­ge­tic app­li­ca­ti­ons are making RAS qui­te cost inten­si­ve. As a result, this cost pres­su­re often leads to indi­vi­du­al lar­ge-sca­le plants. An unmat­ched advan­ta­ge of RAS is the com­ple­te inde­pen­dence to choo­se a loca­ti­on for the pro­duc­tion, becau­se the­re are no natu­ral waters nee­ded. Simul­ta­ne­ous­ly they fea­ture high sto­cking den­si­ties, while obtai­ning a gre­at water qua­li­ty without losing track of the ani­mal wel­fa­re and with a mini­mal impact on the envi­ron­ment. The SEAWATER Cube its­elf is a recir­cu­la­ti­on sys­tem with all its advan­ta­ges. Addi­tio­nal­ly, this deve­lo­ped sys­tem is a stan­dar­di­zed small-sca­le plant for regio­nal production.

The SEAWATER Cube its­elf is a recir­cu­la­ti­on sys­tem with all its advan­ta­ges. Addi­tio­nal­ly, this deve­lo­ped sys­tem is a stan­dar­di­zed small-sca­le plant for regio­nal production.

Further informationen about the SEAWATER Cube

Check out more facts about our sys­tem and the technology.

Refe­ren­ces

FAO (Food And Agri­cul­tu­re Orga­ni­sa­ti­on Of The United Nati­ons), 2016. The Sta­te Of World Fishe­ries and Aquacul­tu­re. Rome
—  Green­peace: https://www.greenpeace.de/themen/meere/welche-aquakulturmethoden-gibt-es (21.02.2018)
— Tim­mons, M.B. & Ebe­ling, J.M., 2010. Recir­cu­la­ting Aquacul­tu­re. 2nd ed. New York: Caya­gua Aqua Ventures

Image source
Cour­te­sy of FAO Aquacul­tu­re Pho­to Library

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