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