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!

Schreckstoff

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This piranha may look scary, but when it's scared, it will release Schreckstoff

This piranha may look scary, but when it’s scared, it will release Schreckstoff

Happy Halloween!

Schreckstoff, German for “scary stuff,” is a chemical compound, glycosaminoglycan chondroitin, that some fish species release when they are injured.  This “take-one -for-the-team” signal lets their conspecifics know that there is danger in the area.  But more than just an alarm signal, Schreckstoff also serves as an immune response for the injured individual, warding off parasites and pathogens such as molds, trematodes, and solar radiation.  Schreckstoff is utilized by fish superorder, Ostariophysi, such as minnows, catfishes, and characiformes (including piranha and tetras), and has also been documented in other species, such as salmonids.

For more information, please visit: The Fisheries Blog‘s post on “Scary Stuff!“

Meristics and Morphometrics

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Meristic and morphometric traits are used to identify fish

Meristic and morphometric traits are used to identify fish

A meristic is a countable trait, such as number of gill rakers or number of dorsal fin spines.  Morphometrics examines the size and shape using a measurable trait, such as standard length or wet weight, which can be gauged as a length, mass, angle or ratio of other measurements.  Meristic traits and morphometrics are often used to classify taxa, sometimes down to the species level or sub-species level.  In dichotomous keys, these counts and measurements can help identify a particular species of fish.  Prior to modern genetic techniques, meristics and morphometrics were the principal foundation for fish taxonomy and systematics.  Even today, meristics and morphometrics are commonly used for species identification and ground-truthing genetic analyses with phenotypic traits.

Habitat

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Fish out of water! Mudskippers have a very unique habitat

Fish out of water! Mudskippers have a very unique habitat

Habitat, is simply, the location where a fish lives.  It applies to any and all life stages.  It is where a fish survives, feeds, grows, and reproduces.  The habitat of a fish depends on the species, from wetlands, to rivers, to coral reefs, to lakes, and more.

Most fish do require well-oxygenated water.  But, there are a few exceptions in which fish have evolved to tolerate low oxygen conditions or even low water conditions.  Mudskippers (family Gobiidae; subfamily Oxudercinae), for example, are amphibious fish that are adapted to intertidal zones.  Some live in mud flat habitat that is only covered in water at high tides.

Habitat is where it’s at!

For more information, please visit:

Recruitment

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In fisheries, recruitment is the number of fish that survive to enter a fishery

In fisheries, recruitment is the number of fish that survive to enter a fishery

In fisheries, recruitment refers to the number of fish surviving to enter a fishery.  These fish have to pass through a number of life history stages (e.g., egg, larva, juvenile, etc.) before becoming vulnerable to fishing gear.

 

Understanding recruitment dynamics is a very complex process – dependent upon the spawning stock biomass and environmental factors.  In some species, recruitment is density dependent; in many of these cases, a larger number of spawners will produce fewer recruits per individual because of competition between larval fish, cannibalism by adults, and other factors.  In many species, 99% of mortality occurs at the egg stage.  This is just one of the many things that make it difficult to forecast population assessments for fish species.

Overfishing, overfished

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The terms overfishing and overfished are confusing because they address a similar subject.  The difference between the two terms is subtle but significant.

Status of overfishing and overfished species monitored by the National Oceanic and Atmospheric Administration (NOAA)

Status of overfishing and overfished species monitored by the National Oceanic and Atmospheric Administration (NOAA)

Overfishing refers to the current fishing rate which results in a higher harvest, or fishing mortality rate, than maximum sustainable yield (the maximum harvest level without negatively impacting the sustainability of the stock).  Overfishing is generally divided into two classes:

  • growth overfishing: where fish are harvested at a size smaller than would produce maximum yield per fish.
  • recruitment overfishing: where the reproductive capacity of a stock is diminished to a point where the spawning stock biomass is not sufficient to maintain the sustainability of a stock.

Overfished, on the other hand, is the state of a stock upon which overfishing has occurred.  The stock is no longer able to produce at a maximum sustainable yield.  It is important to note that a stock may be overfished, but overfishing may not be occurring.  Stocks that are overfished can be managed for fishing pressure that is low enough to allow the stock to rebuild to a level to support maximum sustainable yield.

For more information, please visit:

  • http://www.fishwatch.gov/features/overfishing_overfished_same_thing.htm
  • http://www.nmfs.noaa.gov/stories/2013/05/05_02_13status_of_stocks_2012.html

Teleost

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A Slingjaw Wrasse is an extreme example of a teleost's protrusible jaw

A Slingjaw Wrasse is an extreme example of a teleost’s protrusible jaw.

Teleosts are the most diverse group of fishes (over 26,500 extant species).  Over half of all living vertebrate species are teleosts.  Teleosts are characterized by a protrusible jaw (musculature gives them the ability to move their maxilla and premaxilla) and a symmetrical tail (their spine that ends at the caudal peduncle unlike, for example, sharks).  Teleosts are estimated to have evolved during the Triassic period. By the end of the Cretaceous, the fossil record shows that teleosts dominated both freshwater and marine habitats.