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.

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