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.