Cohort model

Alrea­dy in the Midd­le Ages, mon­ks divi­ded their carp ponds into sec­tions of dif­fe­rent sizes. Even today, the sepa­ra­ti­on of the far­med fish into so-cal­led cohorts is still used. But what is this divi­si­on actual­ly good for?

The basic idea behind the cohort model is to sepa­ra­te the smal­ler fish from the lar­ger ones. Espe­cial­ly with pre­d­a­to­ry fish (car­ni­vo­res), this pre­vents the lar­ger fish from snatching away the exis­ting food through phy­si­cal supe­rio­ri­ty or even eating the smal­ler ones.

Today, in the time of ultra­mo­dern, tech­ni­cal (clo­sed) aquacul­tu­re sys­tems, the­re are even more rea­sons for cohort models:

Pro­duc­tion relia­bi­li­ty: As stan­dard, sepa­ra­ti­on is done by means of round tanks of dif­fe­rent sizes. Here, the ani­mals can be sepa­ra­ted not only spa­ti­al­ly, but most­ly also by inde­pendent­ly working water cir­cuits. Thus, in case of ill­ness, only one tank with its stock (batch) is affec­ted and must be trea­ted or emer­gen­cy kil­led. The remai­ning bat­ches in other tanks remain undamaged.

Fee­ding: Both the amount of feed and the size of the feed pel­lets depend on the size and weight of the ani­mals. Sin­ce the fish are divi­ded into cohorts accord­ing to size and weight class, they can be fed with the appro­pria­te pel­let size in a very pre­cise and resour­ce-saving way.

Avai­la­bi­li­ty: A cohort model also ensu­res con­ti­nuous pro­duc­tion. Among the cohorts, the­re is always one in which the ani­mals have reached mar­ket matu­ri­ty. At the same time, new autumn fries are alrea­dy being used in other cohorts, so that a con­ti­nuous cycle of fishing and resto­cking is crea­ted across all tank areas.

Plant sta­bi­li­ty: Modern aquacul­tu­re plants no lon­ger work only with natu­ral water exchan­ge (e.g. from sea or river) to keep the water clean. Today, fil­ter tech­no­lo­gies (e.g. drum fil­ters, bio­fil­ters, deni­tri­fi­ca­ti­on, …) are used to remo­ve unused food and excre­ments of the fish from the water without pol­lu­ting the natu­ral waters or the envi­ron­ment. The­se fil­ters are par­ti­cu­lar­ly sta­ble and effi­ci­ent when they have about the same amount of work to do every day. Due to the cohorts and the resul­ting balan­ce of fish and rep­le­nish­ment, the­re is always about the same amount of bio­mass in the plant. This in turn means that the amount of feed per day also fluc­tua­tes very litt­le around the average value. The fil­ters are desi­gned in such a way that they opti­mal­ly and ener­gy-effi­ci­ent­ly break down the average amount of excre­ta and residues.

In the SEAWATER Cube we work with a sin­gle lar­ge tank. Nevertheless, in this three cohorts of dif­fe­rent sizes are sepa­ra­ted by net con­struc­tions. Sin­ce the growth of sea bass up to its mar­ket weight of about 400 grams takes about 12 mon­ths, the ani­mals live in one cohort for 4 mon­ths each. After that, they are trans­fer­red to the next cohort through a sluice in the net con­struc­tion without machi­nes or contact.

Further informationen about the SEAWATER Cube

Check out more facts about our sys­tem and the technology.


FAO (Food And Agri­cul­tu­re Orga­ni­sa­ti­on Of The United Nati­ons), 2016. The Sta­te Of World Fishe­ries and Aquacul­tu­re. Rome
Euro­pean Inland Fishe­ries Advi­so­ry Com­mis­si­on, 1986
Wu, R.S.S., 1995. The envi­ron­men­tal impact of mari­ne fish cul­tu­re: Towards a sus­tainab­le future. Mari­ne Pol­lu­ti­on Bul­le­tin 31, pp.159–66
Suma­ri, O., 1982. A report on fish farm efflu­ents in Finn­land. Report of the EIFAC Work­shop on Fish-Farm Efflu­ents. EIFAC Tech­ni­cal Papers 41, pp.21–27.
Pil­lay, T.V.R., 2004. Aquacul­tu­re and the envi­ron­ment. Second Edi­ti­on ed. Oxford: Black­well Publi­shing.
— Tim­mons, M.B. & Ebe­ling, J.M., 2010. Recir­cu­la­ting Aquacul­tu­re. 2nd ed. New York: Caya­gua Aqua Ventures.

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