stenotherm

Thermoregulation

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Fish don't sweat to regulate their body temperature but they do have strategies for thermoregulation (www.fishlady.us).

Fish don’t sweat to regulate their body temperature but they do have strategies for thermoregulation (www.fishlady.us).

Thermoregulation is the process by which an organism controls its internal temperature.  Fish have many different mechanisms for regulating their temperature.  Most fish are ectothermic, using their environmental temperature to manage their body temperature, but some fish are endothermic, having the metabolic ability to internally manage temperature.  Poikilothermic fish are ectotherms which have no control over their body temperature; their core body temperature conforms to ambient temperature.  Eurythermic fish have evolved to survive in a wide range of environmental temperatures and stenothermic fish have evolved to survive in a narrow range of environmental temperatures.

Thermoregulation is very important for fish because temperature influences the function of many organs and the rate of many metabolic processes.  Most fish species have evolved to survive within a specific temperature ranges; outside that range, enzymes can degrade, organs can fail, and the organism can die.  Understanding thermoregulation for fish species is particularly important when considering implications for climate change.

 

Poikilotherm

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Poikilothermic fish have no control over their body temperature and their core body temperature can fluctuate broadly.  While some ectothermic stenotherms thermoregulate their body temperature by inhabiting constant temperature environments, internal temperature of poikilotherms can widely vary.

Thoughout their lives, Steelhead's internal temperature varies considerably (NPS).

Thoughout their lives, Steelhead’s internal temperature varies considerably (NPS).

 

Eurytherm

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Desert Pupfish are eurythermic, surviving in temperatures ranging from function in waters from 4º to 45ºC (Paul V. Loiselle).

Desert Pupfish are eurythermic, surviving in temperatures ranging from function in waters from 4º to 45ºC (Paul V. Loiselle).

In contrast to stenotherms, eurythermic fish can function at a wide range of water temperatures.  They are often, but not necessarily, ectotherms.  Desert Pupfish (Cyprinodon macularius), for example, can function in ambient temperatures ranging from 4 to 45 degrees Celsius.  This thermoregulatory strategy requires that organs, enzymes, and metabolic processes can operate at varying environmental temperatures.

 

Stenotherm

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Brook Trout can only survive in a narrow band of temperatures (FWS).

Brook Trout can only survive in a narrow band of temperatures (FWS).

In contrast to eurytherms, senothermic fish can only function in a narrow range of water temperatures.  Brook Trout (Salvelinus fontinalis), for example, function optimally approximately between 13 and 18 degrees Celsius.  This thermoregulatory strategy requires that organs, enzymes, and metabolic processes operate in a small temperature band and makes these fish particularly vulnerable to environmental changes.

 

Ectotherm

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Ectothermic fish rely upon their environment to regulate their temperature (clipartOf.com).

Ectothermic fish rely upon their environment to regulate their temperature (clipartOf.com).

Unlike endotherms which can metabolically control their own body temperature, ectotherms rely upon environmental temperatures for thermoregulation.  Most fish are ectotherms.  Ectothermy can be metabolically more efficient than endothermy because organisms do not have to expend any energy to self-regulate their body temperatures.  However, they are at the mercy of their environment more than endotherms because they use ambient water temperature to control their body temperature.

Poikilothermic fish have no control over their body temperature whatsoever.  Their core body temperature conforms entirely to ambient temperature and can fluctuate widely. This means that their organs and enzymes need to be capable of functioning at a range of temperatures.  As physiological processes have often evolved to operate most efficiently at certain temperatures, ectothermic fish have evolved multiple strategies to maintain optimal thermal habitat.  Stenotherms live within narrow environmental temperatures in contrast with eurytherms which can live in a wide range of environmental temperatures.