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.

 

Endotherm

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Though rare, some fish are able to internally regulate temperature.

Though rare, some fish are able to internally regulate temperature.

Unlike ectotherms, which rely upon environmental temperatures, endotherms are able to metabolically control their body temperature.  This thermoregulatory strategy is rare among fish but is present in tunas and some sharks, including the Great White Shark (Carcharodon carcharias) and Shortfin Mako Shark (Isurus oxyrinchus).  Endothermic tunas and sharks use a network of capillaries in their swimming muscles, the Rete mirabile, as a heat exchanger.  Through counter-current exchange, the heat produced through muscle activity is transported by the blood.  Through this metabolic process, sharks, for example, can maintain a body temperature of 5 – 14°C above ambient water temperature.  This process is an evolutionary advantage for these long distance, migratory fish, allowing them to travel extensive distances and dive deep while maintaining body temperature, conserving energy, and avoiding thermal shock from changes in water temperature.

Tunas are one example of endothermic fish.

Tunas are one example of endothermic fish.

Oceanodromous

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An oceanodromous fish, like an anadromous or catadromous fish, is a migratory fish.  Unlike anadromous or catadromous fish, an oceanodromous fish spends its whole life in salt water.  Many oceanodromous fishes are termed highly migratory species (HMS) because of their ocean basin-sized migration routes.  Many HMS are high trophic level fish and they migrate in search of food in addition to spawning.  Endangered Atlantic Bluefin Tuna (Thunnus thynnus) are one example of a HMS, high trophic level, oceanodromous fish.  They spawn in the Gulf of Mexico and the Mediterranean Sea.  Tagging studies show that the feed all around the Atlantic basin.  Highly prized on the sashimi markets, bluefin spawning aggregations and schooling behavior make them particularly vulnerable to modern fishing techniques.

Atlantic Bluefina Tuna are an example of an oceanodromous fish which is highly migratory but only lives in salt water.

Atlantic Bluefina Tuna are an example of an oceanodromous fish which is highly migratory but only lives in salt water.

For more information, check out the “CAN YOU SAY ANADROMOUS, CATADROMOUS, AMPHIDROMOUS, OCEANODROMOUS, OR POTAMODROMOUS?” post on The Fisheries Blog!

Diadromous

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George S. Myers defined the term diadromous to refer to fish that migrate between fresh and salt water.

George S. Myers defined the term diadromous to refer to fish that migrate between fresh and salt water.

Diadromous fish migrate between fresh and salt water.  This term, coined by George S. Myers in 1949, refers to both anadromous and catadromous fishes.  Diadromous life history strategies have evolved in numerous fish taxa.  The complex life cycles do require complex osmoregulatory adaptation but the advantages of the given environments for specific life stages of the fish outweigh the costs.

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Potamodromous

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A potamodromous fish, like an anadromous or catadromous fish, is a migratory fish.  Unlike anadromous or catadromous fish, a potamodromous fish spends its whole life in fresh water.  Generally, these migrations are for spawning purposes and cover short distances: from an upstream tributary to a mainsteam river or between connected lake and river systems.  Some species, for example the endangered Colorado Pikeminnow (Ptychocheilus lucius) have very extensive fresh water migration routes – reportedly up to 300km.  Like salmon, the pikeminnow uses homing to reach very specific spawning locations with a high degree of fidelity.

The endangered Colorado Pikeminnow migrates long distances only in fresh water.

The endangered Colorado Pikeminnow migrates long distances only in fresh water.

For more information, check out the “CAN YOU SAY ANADROMOUS, CATADROMOUS, AMPHIDROMOUS, OCEANODROMOUS, OR POTAMODROMOUS?” post on The Fisheries Blog!

Inland fisheries

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Inland fisheries account for 40% of global finfish production from 3% of the volume of water on earth.

Inland fisheries account for 40% of global finfish production from 3% of the volume of water on earth.

Inland waters are defined by the United Nations’ Food and Agriculture Organization as the “surface water existing inland including lakes, ponds, streams, rivers, natural or artificial watercourses and reservoirs, and coastal lagoons and artificial waterbodies.”  Inland fisheries, by consequence, are the fishing activities associated with those waterbodies.  Inland fisheries “may involve capture of wild fish or raising of fish through aquaculture.”

For more information, please checkout The Fisheries Blog‘s post on the importance of inland fish and fisheries.

 

Catadromous

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Eels have a unique larval form, leptocephali, which can utilize marine currents to travel long distances.

Eels have a unique larval form, leptocephali, which can utilize marine currents to travel long distances.

A catadromous fish hatches and spawns in salt water but spends most of its life in fresh water.  Catadromous life cycles are much less common than anadromous life cycles.  American and European Eels (Anguilla rostrate and A. anguilla, respectively) are among the more famous fish that utilize this unusual migration pattern.  They have a highly specialized larvae, leptocephali, which resemble a transparent leaf.  Their specialized shape allows leptocephali to ride marine currents to the continental shelf using relatively low amounts of energy.  In coastal waters, they metamorphose into glass eels.  As they continue to grow and start developing pigmentation, they enter the yellow eel phase.  Yellow eels migrate into estuaries and onto fresh water where they will remain until they reach sexual maturity as a silver eel and return out to sea to spawn.

For more information, check out the “CAN YOU SAY ANADROMOUS, CATADROMOUS, AMPHIDROMOUS, OCEANODROMOUS, OR POTAMODROMOUS?” post on The Fisheries Blog!

Bioluminescence

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Splitfin Flashlightfish are thought to produce the brightest glow of any living organism – they can be seen from over 100 feet away!

Splitfin Flashlightfish are thought to produce the brightest glow of any living organism – they can be seen from over 100 feet away!

Bioluminescence is a chemical process by which some fish species can produce their own source of light.  They have light producing organs known as photophores.  The light is emitted from specialized cells called photocytes or from symbiotic fluorescent bacteria that are cultured by the fish in photophores.  Most fish bioluminescence is blue (because blue-green light transmits furthest in water); this helps camouflage fish in open water because their counterillumination matches the ambient ocean color from above.  Other fish use different colors of bioluminescence, such as red or green or white, to reveal fish hidden by counterillumination, distract or confuse fish with bright flashes, or to signal to other fish (e.g., potential mates or members of their school).

For examples of bioluminescent fish, check out the “twinkle twinkle little fish” post on the Fisheries Blog!

Bioluminescent fish don't need twinkle lights to make their season bright!  Happy Holidays! (riverbanks.org)

Bioluminescent fish don’t need twinkle lights to make their season bright!  Happy Holidays! (riverbanks.org)

 

 

Anadromous

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Pacific salmons are well-known examples of anadromy. They live most of their lives at sea but spawn in fresh water

Pacific salmons are well-known examples of anadromy. They live most of their lives at sea but spawn in fresh water

An anadromous fish hatches and spawns in fresh water but spends most of its life in the salt water.  This dual life cycle allows the younger fish to grow and feed in the less perilous fresh water habitats (fewer predators in the smaller systems) and the older, larger fish to grow and feed in the marine systems, where there is a greater prey base.  Migrating between fresh and salt water requires complex osmoregulatory adaptations.  Some species, such as Pacific salmons, only transition between fresh and salt water twice, migrating to salt water early in life and then migrating back to freshwater to spawn once and die (a semelparous reproductive strategy).  Other species, such as Striped Bass (Morone saxatilis) will migrate between fresh and salt water every year to spawn (an iteroparous reproductive strategy).

For more information, check out the “CAN YOU SAY ANADROMOUS, CATADROMOUS, AMPHIDROMOUS, OCEANODROMOUS, OR POTAMODROMOUS?” post on The Fisheries Blog!

Striped bass are anadromous fish that migrate between fresh and salt water every year to spawn

Striped bass are anadromous fish that migrate between fresh and salt water every year to spawn

Electrofishing

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Electrofishing is a survey technique that stuns fish in freshwater

Electrofishing is a survey technique that stuns fish in freshwater

Electrofishing is a survey tool used to estimate species composition, fish abundance, and fish density in freshwater systems using an electrical current.  An electroshocker creates a flow of current between an anode (i.e., ring on a backpack models) and cathode (i.e., rat tail on backpack models) that stuns fish that cross the electric field.  Stunning the fish makes them easier to capture and assess for research and monitoring purposes.  Backpack electroshockers are generally used for smaller, wadeable waterbodies; boat or raft mounted electroshockers are generally used for larger waterbodies.  While electrofishing can be a very effective technique for freshwater, electricity has poor conductivity in salt water.

For an example of boat electrofishing, check out this depletion electrofishing post on the Fisheries Blog!