Water temperature and fish welfare

The water tem­pe­ra­tu­re in aquacul­tu­re sys­tems has a major impact of fish wel­fa­re. Fish are warm-bloo­ded ani­mals, which means that their body tem­pe­ra­tu­re is not con­stant, but adap­ts to the envi­ron­ment. Depen­ding on the spe­ci­es, the­re are dif­fe­rent tole­ran­ce ran­ges. In the fol­lowing, we exp­lain at which water tem­pe­ra­tures dif­fe­rent fish spe­ci­es feel com­for­ta­ble and how chan­ging water tem­pe­ra­tures in clo­sed recir­cu­la­ti­on sys­tems has an influ­ence on the animals.


Fish species and their temperature sensitivity

In gene­ral, the­re is a cer­tain dicho­to­my in Euro­pe regar­ding fish spe­ci­es that are adap­ted to eit­her cold or warm water. For examp­le, fish from the carp fami­ly pre­fer war­mer waters, while fish spe­ci­es such as trout or sal­mon live exclu­si­ve­ly in col­der waters.

Glo­bal­ly, the­re is a wide ran­ge of tem­pe­ra­tures that fish can cope with:

  • Some spe­ci­es, such as ice­fi­sh from the Ant­arc­tic, are abso­lu­te cold spe­cia­lists and can cope with tem­pe­ra­tures below free­zing thanks to spe­cial anti­free­ze proteins.
  • Other fish spe­ci­es, such as the Juli­mes desert carp, love the heat and can be found in a hot spring in Mexi­co at up to 45 °C.
  • Many exo­tic fish spe­ci­es such as the Yel­low­tail King­fi­sh, Barra­mun­di or Red Snap­per live in warm water of 26 °C and above.
  • Shrimps feel com­for­ta­ble at tro­pi­cal tem­pe­ra­tures of around 30 °C.

But the­re are also tem­pe­ra­tu­re experts in Euro­pe:

  • The cru­ci­an as a carp fish, can per­se­ve­re in the fro­zen mud without oxy­gen for several mon­ths in winter.
  • A Roma­ni­an rudd spe­ci­es also likes to inha­bit warm springs and can cope with as much as 35 °C.
  • The com­mon food fish sea bass and dora­do tole­ra­te tem­pe­ra­tures bet­ween 18 and 28 °C.
  • Sal­mon pre­fer tem­pe­ra­tures bet­ween 9 and 17 °C in the adult stage.
  • Rain­bow trout also tole­ra­te tem­pe­ra­tures bet­ween 10 and 18 °C, but 20 °C should not be exceeded.
Effects of water temperature on fish welfare

As warm-bloo­ded ani­mals, fish are very depen­dent on water tem­pe­ra­tu­re. It deter­mi­nes their acti­vi­ty and direct­ly influ­en­ces important pro­ces­ses such as fee­ding and repro­duc­tion. The tole­ran­ce for tem­pe­ra­tu­re chan­ges depends on several fac­tors. The­se are mainly:

  • the sta­ge in the life cycle
  • the phy­sio­lo­gi­cal state
  • the speed of tem­pe­ra­tu­re changes

Espe­cial­ly embry­os in the egg as well as adults rea­dy to spawn have a very limi­ted tole­ran­ce. Well-fed fish have a high chan­ce of sur­vi­ving a tem­pe­ra­tu­re chan­ge, while sick and star­ving fish reach their limits early.

If tem­pe­ra­tu­re chan­ges occur very sud­den­ly and to a gre­at extent, fish expe­ri­ence stress. In addi­ti­on, their acti­vi­ty is redu­ced in extre­me water tem­pe­ra­tures. Fur­ther­mo­re, the appe­ti­te of the ani­mals is redu­ced. The grea­ter pro­li­fe­ra­ti­on of bac­te­ria in warm water also has a direct effect on their health. Fish with a weak immu­ne sys­tem or open spots on the skin can be atta­cked by patho­gens and fur­ther wea­ke­ned or even die.

Fish and the climate crisis

His­to­ri­cal­ly, cli­ma­te has always had a major influ­ence on water tem­pe­ra­tures and fish. The cur­rent dis­tri­bu­ti­on of freshwa­ter fish spe­ci­es in the tem­pe­ra­te and sub­po­lar zones is lar­ge­ly the result of the lar­ge-sca­le extinc­tion of fish spe­ci­es during the last ice age. Tro­pi­cal and sub­tro­pi­cal waters are richer in spe­ci­es com­pa­red to our nati­ve waters, becau­se the­re was no extinc­tion of fish spe­ci­es due to the cold.

Nowa­days, we see a trend in the oppo­si­te direc­tion. Glo­bal war­ming is the gre­at chal­len­ge of our time and is also a huge pro­blem for fish. It affects fish and their aqua­tic eco­sys­tems in many ways. For examp­le, one direct effect of rising tem­pe­ra­tures is incre­a­sing eva­po­ra­ti­on of sur­face water. In some regi­ons, this can lead to the dry­ing up and disap­pearan­ce of still and flowing waters and their fish. Con­ver­se­ly, floo­ding and high water can also cau­se an imba­lan­ce. They flush fish out of their natu­ral habi­tat, and the­re is spa­ti­al dis­pla­ce­ment of popu­la­ti­ons, up to and inclu­ding extinc­tion of tho­se that can­not find suf­fi­ci­ent food in other waters or can­not tole­ra­te the living con­di­ti­ons. Ano­t­her nega­ti­ve effect is the incre­a­se in extre­me wea­ther (floo­ds, droughts, heat waves, cold waves, storms), which ine­vi­ta­b­ly cau­ses unrest in natu­ral waters and can lead to spe­ci­es loss in the long term.

Some stu­dies have iden­ti­fied fish spe­ci­es that are par­ti­cu­lar­ly vul­nerable to cli­ma­te chan­ge (tro­pi­cal mari­ne fish are thought to be espe­cial­ly at risk) and are alrea­dy docu­men­ting effects of cli­ma­te chan­ge on fish fau­na (popu­la­ti­on decli­nes, incre­a­sed growth, and tem­po­ral chan­ges in migra­ti­on and spaw­ning beha­vi­or). Nevertheless, it is still dif­fi­cult to pre­dict when and whe­re major chan­ges in fish fau­na will occur. In par­ti­cu­lar, the inter­ac­tions of the cli­ma­te cri­sis with other pro­ble­ma­tic human-indu­ced pro­ces­ses such as aqua­tic eutro­phi­ca­ti­on, the spread of inva­si­ve spe­ci­es, and envi­ron­men­tal pol­lu­ti­on and degra­dati­on are elu­si­ve. They have the poten­ti­al to fur­ther worsen the pre­ca­rious situa­ti­on of sca­led species.

So it’s up to all of us to stop cli­ma­te chan­ge and ensu­re that the diver­si­ty of aqua­tic life is pre­ser­ved for future genera­ti­ons to expe­ri­ence. Sus­tainab­le recir­cu­la­ting aquacul­tu­re can be part of the solution.

Further information

Dis­co­ver more about inno­va­ti­ve recir­cu­la­ting aquacul­tu­re systems.


  • Dela­ney, R.G., S. Lahi­ri, and A.P. Fish­man, Aes­ti­va­ti­on of the Afri­can lung­fi­sh Protop­te­rus aethio­pi­cus: car­dio­vascu­lar and respi­ra­to­ry func­tions. Jour­nal of Expe­ri­men­tal Bio­lo­gy, 1974. 61(1): p. 111–128.
  • Dah­l­ke, F.T., et al., Ther­mal bot­t­len­ecks in the life cycle defi­ne cli­ma­te vul­nera­bi­li­ty of fish. Sci­ence, 2020. 369(6499): p. 65–70.
  • Jones, A., Ther­mal and deve­lo­p­men­tal eco­lo­gy of pup­fi­sh, Cyprinodon.
  • Lefe­v­re, S., et al., Re-oxy­ge­na­ti­on after anoxia indu­ces brain cell death and memo­ry loss in the anoxia-tole­rant cru­ci­an carp. Jour­nal of Expe­ri­men­tal Bio­lo­gy, 2017. 220(21): p. 3883–3895.
  • Mül­ler, T., et al., Arti­fi­cial pro­pa­ga­ti­on of the end­an­ge­red Ruma­ni­an ende­mic warm water rudd (Scar­di­ni­us raco­vitzai Mül­ler 1958, Cypri­ni­dae, Cypri­ni­for­mes) for con­ser­va­ti­on needs. The Egyp­ti­an Jour­nal of Aqua­tic Rese­arch, 2018. 44(3): p. 245–249.
  • Siv­a­ku­mar, M.V.K., Inter­ac­tions bet­ween cli­ma­te and deser­ti­fi­ca­ti­on. Agri­cul­tu­ral and Forest Meteo­ro­lo­gy, 2007. 142(2): p. 143–155.
  • Leib­niz-Insti­tut Für Gewäs­ser­öko­lo­gie Und, B., R. Adri­an, and T. Shat­well, Dia­gno­sen und Pro­gno­sen aus der Lang­zeit­for­schungS­e­en im Klimawandel.
  • Comte, L. and J.D. Olden, Cli­ma­tic vul­nera­bi­li­ty of the world’s freshwa­ter and mari­ne fishes. Natu­re Cli­ma­te Chan­ge, 2017. 7(10): p. 718–722.
  • Myers, B.J.E., et al., Glo­bal syn­the­sis of the docu­men­ted and pro­jec­ted effects of cli­ma­te chan­ge on inland fishes. Reviews in Fish Bio­lo­gy and Fishe­ries, 2017. 27(2): p. 339–361.
  • Bun­des­ver­band Aquakultur

Newsletter abonnieren

Du möchtest regelmäßige Updates zu SEAWATER Cubes erhalten? In unserem monatlichen Newsletter informieren wir zu aktuellen Themen und Entwicklungen rund um unser Unternehmen. Außerdem warten spannende Fachbeiträge zum Thema Aquakultur sowie exklusive Informationen zu Veranstaltungen auf Dich.

Vielen Dank! Du hast Dich erfolgreich für unseren Newsletter angemeldet.