Demersal fish

{{short description|Fish that live and feed on or near the bottom of seas or lakes}} {{use British English|date=August 2021}} {{use dmy dates|date=August 2021}} [[File:Stingray.jpg|thumb|300px|right|[[Bluespotted ribbontail ray]] resting on the [[seafloor]]]] [[File:Rhinogobius flumineus(Hamamatsu,Shizuoka,Japan).jpg|thumbnail|right|''[[Rhinogobius flumineus]]'' swim on the beds of [[river]]s]]

'''Demersal fish''', also known as '''groundfish''', live and feed on or near the bottom of [[ocean|sea]]s or [[lake]]s (the [[demersal zone]]).<ref name="seafloor">Walrond C [http://www.teara.govt.nz/en/coastal-fish/5 Carl . "Coastal fish - Fish of the open sea floor"] Te Ara - the Encyclopedia of New Zealand. Updated 2 March 2009</ref> They occupy the sea floors and lake beds, which usually consist of mud, sand, gravel or rocks.<ref name="seafloor" /> In coastal waters, they are found on or near the [[continental shelf]], and in deep waters, they are found on or near the [[continental slope]] or along the continental rise. They are not generally found in the deepest waters, such as [[Abyssal zone|abyssal]] depths or on the [[abyssal plain]], but they can be found around [[seamount]]s and islands. The word ''demersal'' comes from the [[Latin]] ''demergere'', which means ''to sink''. Demersal fish are [[bottom feeder]]s. They can be contrasted with [[pelagic fish]], which live and feed away from the bottom in the open [[water column]]. Demersal fish fillets contain little [[fish oil]] (one to four per cent), whereas pelagic fish can contain up to 30 per cent.{{Not verified in body|date=May 2018}}

==Types== [[File:Jan van Kessel 004.jpg|thumb|right| Benthic [[flatfish]] and benthopelagic [[cod]] on a shore – [[Jan van Kessel, senior|Jan van Kessel]] senior, 1626–1679]]

Demersal fish can be divided into two main types: strictly [[Benthic zone|benthic]] fish which can rest on the sea floor, and benthopelagic fish which can float in the [[water column]] just above the sea floor.

Benthopelagic fish have [[neutral buoyancy]], so they can float at depth without much effort, while strictly benthic fish are denser, with negative buoyancy so they can lie on the bottom without any effort.<ref name="Bone42" /> Most demersal fish are benthopelagic.<ref name="seafloor" />

As with other bottom feeders, a mechanism to deal with [[Substrate (marine biology)|substrate]] is often necessary. With demersal fish the sand is usually pumped out of the mouth through the [[gill slit]]. Most demersal fish exhibit a flat ventral region so as to more easily rest their body on the substrate. The exception may be the [[flatfish]], which are laterally depressed but lie on their sides. Also, many exhibit what is termed an "inferior" mouth, which means that the mouth is pointed downwards; this is beneficial as their food is often below them in the substrate. Those bottom feeders with upward-pointing mouths, such as [[Stargazer (fish)|stargazer]]s, tend to seize swimming prey.

===Benthic fish=== Benthic fish are denser than water, so they can rest on the sea floor. They either lie-and-wait as [[ambush predator]]s, at times covering themselves with sand or otherwise camouflaging themselves, or move actively over the bottom in search for food.<ref name="Moyle588"/> Benthic fish which can bury themselves include [[flatfish]], [[stingray]]s and [[dragonets]].

[[Flatfish]] are an [[order (biology)|order]] of [[ray-finned fish|ray-finned]] benthic fishes which lie flat on the ocean floor. Examples are [[flounder]], [[sole (fish)|sole]], [[turbot]], [[plaice]], and [[halibut]]. The adult fish of many species have both eyes on one side of the head. When the fish hatches, one eye is located on each side of its head. But as the fish grows from the larval stage, one eye migrates to the other side of the body as a process of [[metamorphosis]]. The flatfish then changes its habits, and camouflages itself by lying on the bottom of the ocean floor with both eyes facing upwards.<ref>{{cite journal |last1=Fairchild, E.A. and Howell, W.H |title=Factors affecting the post-release survival of cultured juvenile Pseudopleuronectes americanus |journal=Journal of Fish Biology |volume=65 |issue=Supplementary A |pages=69–87 |url=http://cinemar.unh.edu/fisheries/stock_enhancement/05_jfb529.pdf |doi=10.1111/j.0022-1112.2004.00529.x |year=2004 |first1=E. A. |last2=Howell |first2=W. H. |url-status=dead |archive-url=https://web.archive.org/web/20070818224817/http://cinemar.unh.edu/fisheries/stock_enhancement/05_jfb529.pdf |archive-date=2007-08-18 |citeseerx=10.1.1.532.3120 }} July 17, 2004. Accessed 2009-06-08.</ref> The side to which one eye migrates depends on the species; with some species both eyes are ultimately on the left side, whereas with other species the eyes are on the right.

<gallery heights="110" mode="packed" style="float:left;"> File:Pseudopleuronectes americanus.jpg|[[Flounder]] have both eyes on one side of their head File:Flounder camo md.jpg|Some flatfish can camouflage themselves on the ocean floor File:Taeniura lymma 2.jpg|[[Bluespotted ribbontail ray]]s migrate in schools onto shallow sands to feed on mollusks, shrimps, crabs and worms.<ref>{{fishbase species|genus=Taeniura|species=lymma|month=August|year=2009}}</ref> File:Sphyrna mokarran head.jpg|The [[great hammerhead]] detects the electrical signatures of stingrays buried in the sand and pins them with its "hammer".<ref>{{Cite web|title=Sandy Plains: Great Hammerhead Shark|url=http://www.elasmo-research.org/education/ecology/sandy-gt_hammerhead.htm|access-date=2022-01-19|website=www.elasmo-research.org}}</ref> </gallery> {{clear}}

Flounder ambush their prey, feeding at soft muddy area of the sea bottom, near bridge piles, docks, artificial and coral reefs. Their diet consists mainly of fish spawn, [[crustacean]]s, [[polychaete]]s and small fish.

The [[great hammerhead]] swings its head in broad angles over the sea floor to pick up the electrical signatures of stingrays buried in the sand. It then uses its "hammer" to pin down the stingray.<ref name="hammerschlag">Hammerschlag, Rick. [http://www.elasmo-research.org/education/ecology/sandy-gt_hammerhead.htm Sandy Plains: Great Hammerhead Shark]. ''ReefQuest Centre for Shark Research''. Retrieved: 6 June 2022.</ref>

<gallery heights="110px" mode="packed" style="float:left;"> File:Pacific hagfish Myxine.jpg|[[Pacific hagfish]] resting on bottom. Hagfish coat themselves and any dead fish they find with noxious slime making them inedible to other species. File:Bathypterois grallator.jpg|The tripodfish (''[[Bathypterois grallator]]''), a species of spiderfish, uses its fin extensions to "stand" on the bottom.<ref>{{FishBase species|genus=Bathypterois|species=grallator|year=2009|month=August}}</ref> File:Caelorinchus mirus (Gargoyle fish).gif|[[Gargoyle fish]] File:Fringe-Lipped Flathead.jpg|The [[Flathead (fish)|fringe-lipped flathead]] is found in estuaries </gallery> {{clear}}

Some fishes do not fit into the above classification. For example, the family of nearly blind [[spiderfish]]es, common and widely distributed, feed on benthopelagic zooplankton. Yet they are strictly benthic fish, since they stay in contact with the bottom. Their fins have long rays they use to "stand" on the bottom while they face the current and grab zooplankton as it passes by.<ref>Sulak KJ () [https://doi.org/10.1007%2FBF02905424 "The systematics and biology of ''Bathypterois (Pisces, Chlorophthalmidae)'' with a revised classification of benthic myctophiform fishes"] ''Ichthyological Research'', '''32'''(4)443-446.</ref>

The bodies of benthic fish are adapted for ongoing contact with the sea floor. Swimbladders are usually absent or reduced, and the bodies are usually flattened in one way or another.<ref name="Moyle13">Moyle and Cech, 2004, p. 13</ref> Following Moyle and Cech (2004) they can be divided into five overlapping body shapes:<ref name="Moyle13" />

{| class="wikitable" |- ! colspan="3"| Body types of benthic fish |- ! Bottom rovers | width=140px | [[File:bluecat5A.jpg|140px|center|[[Blue catfish]]]] | Bottom rovers "have a rover-predator-like body, except that the head tends to be flattened, the back humped, and the pectoral fins enlarged. [[Ictaluridae|North American catfish]] with large mouths at the end of the snout, small [[Loricariidae|armoured catfish]] with small mouths beneath the snout, and [[sturgeon]]s, with fleshy protusible lips located well below the snout that are used to suck plant and animal matter off the bottom."<ref name="Moyle14">Moyle and Cech, 2004, p. 14</ref> |- ! Bottom clingers | [[File:Rhinogobius duospilus.jpeg|140px|center|Two freshwater gobies, ''[[Rhinogobius duospilus]]'']] | Bottom clingers "are mainly small fish with flattened heads, large pectoral fins, and structures (usually modified pelvic fins) that enable them to adhere to the bottom. Such structures are handy in swift streams, or intertidal areas with strong currents. The simplest arrangement is possessed by [[sculpin]]s, which use their small, closely spaced pelvic fins, as antiskid devices. However, other families of fishes, such as [[Goby|gobies]], and [[clingfish]]es have evolved suction cups."<ref name="Moyle14"/> |- ! Bottom hiders | [[File:Ammocrypta bifascia.jpg|140px|center|[[Florida sand darter]], ''Ammocrypta bifascia'']] | Bottom hiders "are similar in many ways to bottom clingers. but they lack the clinging devices and tend to have more elongate bodies and smaller heads. These forms usually live under rocks or in crevices or lie quietly on the bottom in still waters. The [[Etheostomatinae|darters]] of North American streams are in the category, as are many [[blenny|blennies]]."<ref name="Moyle14"/> |- ! Flatfish | [[File:Hippoglossoides platessoides.jpg|140px|center|[[American plaice]]]] | Flatfish "have the most extreme morphologies of the bottom fish. [[Flounder]]s are essentially deep-bodied fish which live with one side on the bottom. In these fish, the eye on the downward side migrates during development to the upward side, and the mouth often assumes a peculiar twist to enable bottom feeding. In contrast, [[Skate (fish)|skate]]s and [[Batoidea|ray]]s are flattened [[dorsoventral]]ly, and mostly move about by flapping their extremely large [[pectoral fin]]s. Not only is the mouth completely [[ventral]] on these fish, the main water intakes for respiration (the [[Spiracle (vertebrates)|spiracle]]s) are located on the top of the head."<ref name="Moyle14"/> |- ! Rattail-shaped fish | [[File:Hephthocara simum.jpg|140px|center|[[Viviparous brotula]]]] | Rattail-shaped fish "have bodies that begin with large pointy-snouted heads and large [[pectoral fin]]s and end in long pointed rat-like tails. These fish are almost all bottom-dwelling (benthic) inhabitants of the deep sea, but exactly why this peculiar morphology is so popular among them is poorly understood. The fish live by scavenging and preying on benthic invertebrates. Examples are the [[rattail|grenadiers]], [[viviparous brotula]]s (pictured), and [[chimaera]]s."<ref name="Moyle14"/> |}

===Benthopelagic fish=== [[File:Pseudotriakis microdon 1.jpg|thumb|right|The sluggish bathydemersal [[false catshark]], shown here at a depth of 1,200 meters, has an enormous [[shark liver oil|oil-filled liver]] which lets it hover off the continental slope at near-[[neutral buoyancy]]. It feeds on cephalopods, [[cutthroat eel]]s, [[Rattail|grenadier]]s, [[snake mackerel]], and [[lanternshark]]s.<ref>{{cite book |author=Compagno, Leonard J.V. |year=1984 |title=Sharks of the World: An Annotated and Illustrated Catalogue of Shark Species Known to Date |place=[[Rome]] |publisher=[[Food and Agriculture Organization]] |isbn=978-92-5-101384-7}}</ref><ref>Martin, R.A. [http://elasmo-research.org/education/shark_profiles/proscylliidae.htm Procellariidae and Pseudotriakidae: Finback & False Catsharks]. ''ReefQuest Centre for Shark Research''. Retrieved on February 14, 2009.</ref><ref>{{fishbase species |genus=Pseudotriakis |species=microdon |year=2009|month=August}}</ref>]]

Benthopelagic fish inhabit the water just above the bottom, feeding on [[benthos]] and [[zooplankton]].<ref>Mauchline J and Gordon JDM (1986) "Foraging strategies of deep-sea fish"] ''Mar. Ecol. Prog. Ser.'' '''27''': 227-238. [https://www.int-res.com/articles/meps/27/m027p227.pdf Download]</ref> Most demersal fish are benthopelagic.<ref name="seafloor" />

[[Deep sea]] benthopelagic [[teleost]]s all have [[swimbladder]]s. The dominant species, [[rattail]]s and [[cusk eel]]s, have considerable biomass. Other species include deep sea [[cod]]s ([[Moridae|morids]]), deep sea eels, [[halosaur]]s and [[Notacanthiformes|notacanth]]s.<ref name="Bone43">Bone 2008, p. 43.</ref>

Benthopelagic sharks, like the deep sea [[Squaliformes|squaloid sharks]], achieve neutral buoyancy with the use of large [[shark liver oil|oil-filled livers]].<ref name="Bone42">Bone 2008, p. 42.</ref> Sharks adapt well to fairly high pressures. They can often be found on slopes down to about 2000 metres, scavenging on food falls such as [[Whale fall|dead whales]]. However, the energy demands of sharks are high, since they need to swim constantly and maintain a large amount of oil for buoyancy. These energy needs cannot be met in the extreme [[oligotrophic]] conditions that occur at great depths.<ref name="Bone42" />

Shallow water stingrays are benthic, and can lie on the bottom because of their negative buoyancy. Deep sea stingrays are benthopelagic, and like the squaloids have very large livers which give them neutral buoyancy.<ref name="Bone42" />

Benthopelagic fish can be divided into flabby or robust body types. Flabby benthopelagic fishes are like [[bathypelagic fish]]es; they have a reduced body mass, and low metabolic rates, expending minimal energy as they lie and wait to [[Ambush predator|ambush]] prey.<ref>Koslow JA (1996) [https://archive.today/20130106055518/http://www3.interscience.wiley.com/journal/119203567/abstract "Energetic and life-history patterns of deep-sea benthic, benthopelagic and seamount-associated fish"] ''Journal of Fish Biology'', '''49'''(sA) 54-74.</ref> An example of a flabby fish is the [[cusk-eel]] ''Acanthonus armatus'',<ref name="fishbase">{{fishbase species |genus=Acanthonus |species=armatus |year=2009 |month=August}}</ref> a predator with a huge head and a body that is 90 per cent water. This fish has the largest ears ([[otolith]]s) and the smallest brain in relation to its body size of all known vertebrates.<ref name="Fine">Fine ML, Horn MH and Cox B (1987) [http://rspb.royalsocietypublishing.org/content/230/1259/257.abstract "''Acanthonus armatus'', a Deep-Sea Teleost Fish with a Minute Brain and Large Ears"] ''Proceedings of the Royal Society B'', '''230'''(1259)257-265.</ref>

==Habitats== [[File:Continental shelf.svg|thumb|Profile illustrating the shelf, slope and rise]] The edge of the [[continental shelf]] marks the boundary where the shelf gives way to, and then gradually drops into [[abyssal]] depths. This edge marks the boundary between coastal, relatively shallow, benthic habitats, and the deep benthic habitats. Coastal demersal fishes live on the bottom of inshore waters, such as bays and estuaries, and further out, on the floor of the [[continental shelf]]. Deep water demersal fish live beyond this edge, mostly down the [[continental slope]]s and along the continental rises which drop to the [[abyssal plain]]s. This is the [[continental margin]], constituting about 28% of the total oceanic area.<ref name=pjccc>P. J. Cook, Chris Carleton (2000) "Continental Shelf Limits: The Scientific and Legal Interface", {{ISBN|0-19-511782-4}}</ref> Other deep sea demersal fish can also be found around [[seamount]]s and islands.

The term ''bathydemersal fish'' is sometimes used instead of "deep water demersal fish". ''Bathydemersal'' refers to demersal fish which live at depths greater than 200 metres.

The term ''epibenthic'' is also used to refer to organism that live on top of the ocean floor, as opposed to those that burrow into the seafloor substrate. However the terms ''mesodemersal'', ''epidemersal'', ''mesobenthic'' and ''bathybenthic'' are not used.

===Coastal=== {{see also|Coastal fish|Reef fish}}

Coastal demersal fish are found on or near the seabed of coastal waters between the [[shoreline]] and the edge of the [[continental shelf]], where the shelf drops into the deep ocean. Since the continental shelf is generally less than 200 metres deep, this means that coastal waters are generally [[epipelagic]]. The term includes demersal [[reef fish]] and demersal fish that inhabit [[estuaries]], [[inlet]]s and [[bay]]s.

<gallery heights="150px" mode="packed" style="float:left;"> File:Mangrovejack.jpg|The [[mangrove jack]] eats [[crustacean]]s File:Puffer Fish DSC01257.JPG|Many [[puffer fish]] species crush the shells of [[mollusc]]s File:Opsanus beta 1.jpg|The venomous [[Batrachoididae|toadfish]], a [[benthic]] [[ambush predator]], blends into sandy or muddy bottoms.<ref name=FB>{{FishBase family|family=Batrachoididae|year=2009|month=September}}</ref> File:Titan Triggerfish.jpg|[[Triggerfish]] use a jet of water to uncover [[sand dollar]]s buried in sand </gallery> {{clear}}

Young [[mangrove jack]]s, a sought after eating and [[sport fish]], dwell in [[estuaries]] around [[mangrove]] roots, fallen trees, rock walls, and any other snag areas where smaller prey reside for protection. When they mature, they migrate into open waters, sometimes hundreds of kilometres from the coast to spawn.<ref>Russell, D.J., et al., "Biology, Management and Genetic Stock Structure of Mangrove Jack (Lutjanus argentimaculatus) in Australia," The State of Queensland, Department of Primary Industries and the Fisheries Research Development Corporation, FRDC Project Number 1999/122, 2003.</ref><ref>{{cite web|url=http://www.fao.org/figis/servlet/species?fid=3134|title=FAO Fisheries & Aquaculture - Aquatic species|website=www.fao.org|access-date=1 September 2009|archive-date=8 May 2005|archive-url=https://web.archive.org/web/20050508083500/http://www.fao.org/figis/servlet/species?fid=3134|url-status=dead}}</ref>

[[File:Uranoscopus sulphureus.jpg|thumb|240px|right|The [[Stargazer (fish)|stargazer]] ''Uranoscopus sulphureus''<ref>{{FishBase_species |genus=Uranoscopus |species=sulphureus |year=2009 |month=September}}</ref>]]

[[Stargazer (fish)|Stargazer]]s are found worldwide in shallow waters. They have eyes on top of their heads and a large upward-facing mouth. They bury themselves in sand, and leap upwards to ambush benthopelagic fish and [[invertebrate]]s that pass overhead. Some species have a worm-shaped lure growing out of the floor of the mouth, which they wiggle to attract prey. Stargazers are [[venom (poison)|venomous]] and can deliver [[electric shock]]s. They have been called "the meanest things in creation."<ref>{{FishBase family | family = Uranoscopidae | |year=2009 |month=September}}</ref><ref>{{cite web|url=https://www.youtube.com/watch?v=62Bd02FUjcI |archive-url=https://ghostarchive.org/varchive/youtube/20211221/62Bd02FUjcI |archive-date=2021-12-21 |url-status=live|title=Southern Stargazer in Utila, Honduras|last=pixelkatt|date=25 March 2007|via=YouTube}}{{cbignore}}</ref><ref>Grady, Denise [https://www.nytimes.com/2006/08/22/science/22fish.html?ei=5094&en=3d2f666379306107&hp=&ex=1156219200&partner=homepage&pagewanted=print Venom Runs Thick in Fish Families, Researchers Learn] ''[[The New York Times]]'' 22 August 2006.</ref>

Other examples of coastal demersal fish are [[cod]], [[plaice]], [[monkfish]] and [[sole (fish)|sole]].

===Deep water=== [[File:Oceanic basin.svg|thumb|Cross-section of an ocean basin. Note significant [[vertical exaggeration]].]]

Deep water demersal fish occupy the [[Benthic zone|benthic regions]] beyond the continental margins.

On the [[continental slope]], demersal fishes are common. They are more diverse than coastal demersal fish, since there is more habitat diversity. Further out are the [[abyssal plain]]s. These flat, featureless regions occupy about 40 per cent of the ocean floor. They are covered with [[Pelagic sediments|sediment]] but largely devoid of benthic life ([[benthos]]). Deep sea benthic fishes are more likely to associate with canyons or rock outcroppings among the plains, where invertebrate communities are established. Undersea mountains ([[seamount]]s) can intercept deep sea currents, and cause productive upwellings which support benthic fish. Undersea mountain ranges can separate underwater regions into different ecosystems.<ref name="Moyle587">Moyle and Cech, 2004, p. 587</ref>

[[Rattail]]s and [[Ophidiidae|brotula]]s are common, and other well-established families are [[eel]]s, [[eelpout]]s, [[hagfish]]es, [[greeneye]]s, [[Ogcocephalidae|batfish]]es and [[lumpfish]]es.<ref name="Moyle587"/>

The bodies of deep water demersal fishes are muscular with well developed organs. In this way they are closer to [[mesopelagic fish]]es than [[bathypelagic fish]]es. In other ways, they are more variable. [[Photophore]]s are usually absent, eyes and [[swimbladder]]s range from absent to well developed. They vary in size, and larger species, greater than one metre, are not uncommon.

[[File:Giant grenadier.jpg|thumb|left|[[Giant grenadier]], an elongate deep water demersal fish with large eyes and well-developed [[lateral line]]s]]

Deep sea demersal fish are usually long and narrow. Many are [[eel]]s or shaped like eels. This may be because long bodies have long [[lateral line]]s. Lateral lines detect low-frequency sounds, and some demersal fishes have muscles that drum such sounds to attract mates.<ref name="Haedrich1996">Haedrich RL (1996) [https://archive.today/20121017043834/http://www3.interscience.wiley.com/journal/119203565/abstract "Deep-water fishes: evolution and adaptation in the earth's largest living spaces"] ''Journal of Fish Biology'' '''49'''(sA):40-53. </ref> Smell is also important, as indicated by the rapidity with which demersal fish find traps baited with [[bait fish]].

The main diet of deep sea demersal fish is [[invertebrate]]s of the deep sea [[benthos]] and [[carrion]]. Smell, touch and lateral line sensitivities seem to be the main sensory devices for locating these.<ref name="Moyle588">Moyle and Cech, 2004, p. 588</ref>

Like coastal demersal fish, deep sea demersal fish can be divided into benthic fish and benthopelagic fish, where the benthic fish are negatively buoyant and benthopelagic fish are neutrally buoyant.<ref name="Moyle588"/>

The availability of plankton for food diminishes rapidly with depth. At {{Convert|1000|m|ft}}, the biomass of plankton is typically about 1 per cent of that at the surface, and at {{Convert|5000|m|ft}} about 0.01 per cent.<ref name="Bone43" /> Given there is no sunlight, energy enters deep water zones as organic matter. There are three main ways this happens. Firstly, organic matter can move into the zone from the continental landmass, for example, through currents that carry the matter down rivers, then plume along the continental shelf and finally spill down the continental slope. Other matter enters as particulate matter raining down from the overhead water column in the form of [[marine snow]], or as sinking overhead plant material such as [[Zostera|eelgrass]], or as "large particles" such as dead fish and whales sinking to the bottom. A third way energy can arrive is through fish, such as vertically migrating mesopelagic fishes that can enter into the demersal zone as they ascend or descend. The demersal fish and invertebrates consume organic matter that does arrive, break it down and recycle it. A consequence of these energy delivery mechanisms is that the abundance of demersal fish and invertebrates gradually decrease as the distance from continental shorelines increases.<ref name="Moyle594">Moyle and Cech, 2004, p. 594</ref>

Although deep water demersal fish species are not generally picky about what they eat, there is still some degree of specialisation. For example, different fish have different mouth sizes, which determines the size of the prey they can handle. Some feed mostly on benthopelagic organisms. Others fed mostly on [[epifauna]] (invertebrates on top of the seafloor surface, also called ''epibenthos''), or alternatively on [[infauna]] (invertebrates that burrow into the seafloor substrate). Infauna feeders can have considerable sediment in their stomachs. Scavengers, such as [[snubnosed eel]]s and [[hagfish]], also eat infauna as a secondary food source.<ref name="Sedberry">Sedberry GR and Musick JA (1978) [https://doi.org/10.1007%2FBF00390900 "Feeding strategies of some demersal fishes of the continental slope and rise off the mid-Atlantic coast of the USA"] ''Marine Biology'', '''44''':357-375.</ref>

<gallery heights="80px" mode="packed" style="float:left;"> File:Simenchelys parasiticus.jpg|[[Snubnosed eel]] File:Ilyophis brunneus.jpg|[[Muddy arrowtooth eel]] File:Urophycis tenuis.jpg|[[White hake]]<ref>{{FishBase species|genus = Urophycis|species = tenuis|month=August|year=2009}}</ref> </gallery> {{clear}}

Some feed on carrion. Cameras show that when a dead fish is placed on the bottom, vertebrate and invertebrate scavengers appear very quickly. If the fish is large, some scavengers burrow in and eat it from the inside out. Some fish, such as [[Rattail|grenadier]]s, also appear and start feeding on the scavenging invertebrates and [[amphipod]]s. Other specialization is based on depth distribution. Some of the more abundant upper continental slope fish species, such as [[cutthroat eel]] and [[Phycidae|longfinned hake]],<ref>{{fishbase species |genus=Phycis |species=chesteri |month=August |year=2009}}</ref> mainly feed on [[epipelagic fish]]. But generally, the most abundant deep water demersal fish species feed on invertebrates.<ref name="Sedberry" /><ref name="Moyle595">Moyle and Cech, 2004, p. 595</ref>

At great depths, food scarcity and extreme pressure limits the ability of fish to survive. The deepest point of the ocean is about 11,000 metres. [[Bathypelagic fish]]es are not normally found below 3,000 metres.<ref name="nielsen">{{cite journal |title=The deepest living fish ''Abyssobrotula galatheae'': a new genus and species of oviparous ophidioids (Pisces, Brotulidae) |author=Nielsen, J.G. |journal=Galathea Report |year=1977 |volume=14 |pages=41–48}}</ref> It may be that extreme pressures interfere with essential enzyme functions.<ref name="TeAraBZ">Ryan P [http://www.teara.govt.nz/EarthSeaAndSky/SeaLife/DeepSeaCreatures/3/en "Deep-sea creatures: The bathypelagic zone"] {{Webarchive|url=https://web.archive.org/web/20081221020633/http://www.teara.govt.nz/EarthSeaAndSky/SeaLife/DeepSeaCreatures/3/en |date=21 December 2008 }} ''Te Ara - the Encyclopedia of New Zealand''. Updated 21 September 2007.</ref>

The deepest-living fish known, the strictly benthic ''[[Abyssobrotula galatheae]]'', eel-like and blind, feeds on benthic invertebrates. A living example was trawled from the bottom of the [[Puerto Rico Trench]] in 1970 from a depth of 8,370 metres (27,453 ft).<ref>Nielsen JG (1977) "The deepest living fish Abyssobrotula galatheae: a new genus and species of oviparous ophidioids (Pisces, Brotulidae)". ''Galathea Report'', '''14''': 41–48.</ref><ref>{{fishbase species |genus=Abyssobrotula |species=galatheae |month=August |year=2009}}</ref>

In 2008, a shoal of 17 [[Pseudoliparis amblystomopsis|hadal snailfish]], a species of deep water [[snailfish]], was filmed by a UK-Japan team using remote operated landers at depths of {{convert|7.7|km|mi|abbr=on}} in the [[Japan Trench]] in the Pacific. The fish were 30 centimetres long (12 in), and were darting about, using vibration sensors on their nose to catch shrimps. The team also reported that the appearance of the fish, unlike that of most deep sea fish, was surprisingly "cute", and that they were surprised by how active the fish were at these depths.<ref>[http://news.bbc.co.uk/2/hi/science/nature/7655358.stm 'Deepest ever' living fish filmed] ''BBC News'', 7 October 2008.</ref><ref>{{FishBase species|genus=Pseudoliparis|species=amblystomopsis|month=March|year=2009}}</ref>

==Demersal fisheries== {{Update|section|date=November 2017}}

Most demersal fish of commercial or recreational interest are coastal, confined to the upper 200 metres. Commercially important demersal [[food fish]] species include [[flatfish]], such as [[flounder]], [[sole (fish)|sole]], [[turbot]], [[plaice]], and [[halibut]]. Also important are [[cod]], [[hake]], [[redfish]], [[haddock]], [[Bass (fish)|bass]], [[conger]]s, [[shark]]s, [[Batoidea|ray]]s and [[chimaera]]s.<ref name="Grainger & Garcia 1996">Grainger RJK and Garcia SM (1996) [http://www.fao.org/docrep/003/W3244E/w3244e00.htm#Contents "Chronicles of Marine Fishery Landings (1950-1994): Trend Analysis and Fisheries Potential"] ''[[FAO]]: Fisheries technical paper 359.'' Rome. {{ISBN|92-5-103899-6}}.</ref>

The following table shows the world capture production of some groups of demersal species in tonnes.<ref>[[FAO]] (2006) [https://web.archive.org/web/20170518134931/ftp://ftp.fao.org/FI/STAT/summary/default.htm ''Yearbooks of Fishery Statistics Summary Tables'']</ref> {| class="sortable wikitable" |- ! colspan=9 align="center" width="640px"| Capture production by groups of species in tonnes |- ! width="100"| Group ! 1999 ! 2000 ! 2001 ! 2002 ! 2003 ! 2004 ! 2005 | rowspan=4 | [[File:2005demersal fish.PNG|thumb|250px|Demersal fish output in 2005]] |- | [[Cod]]s, [[hake]]s, [[haddock]]s | align="right"| 9,431,141 | align="right"| 8,695,910 | align="right"| 9,304,922 | align="right"| 8,474,044 | align="right"| 9,385,328 | align="right"| 9,398,780 | align="right"| 8,964,873 |- | [[Flounders]], [[halibut]]s, [[Sole (fish)|soles]] | align="right"| 956,926 | align="right"| 1,009,253 | align="right"| 948,427 | align="right"| 915,177 | align="right"| 917,326 | align="right"| 862,162 | align="right"| 900,012 |- | Other demersal fishes | align="right"| 2,955,849 | align="right"| 3,033,384 | align="right"| 3,008,283 | align="right"| 3,062,222 | align="right"| 3,059,707 | align="right"| 3,163,050 | align="right"| 2,986,081 |- |}

[[Black sea bass]] inhabit US coasts from [[Maine]] to NE [[Florida]] and the eastern [[Gulf of Mexico]], and are most abundant off the waters of [[New York (state)|New York]]. They are found in inshore waters (bays and sounds) and offshore in waters up to a depth of 130 m (425'). They spend most of their time close to the sea floor and are often congregated around bottom formations such as rocks, [[man-made reef]]s, wrecks, jetties, piers, and [[bridge pilings]]. Black sea bass are sought after recreational and commercial fish, and have been [[Overfishing|overfished]].<ref name="striata">{{FishBase species | genus = Centropristis | species = striata | month = August | year = 2009}}</ref>

<gallery heights="110px" mode="packed" style="float:left;"> File:Hippoglossoides platessoides.jpg|[[American plaice]] are usually found between 90 and 250 metres (but have been found at 3000 m). They feed on small fishes and invertebrates.<ref>{{fishbase species|genus=Hippoglossoides|species=platessoides|month=August|year=2009}}</ref> File:Atlantic cod.jpg|[[Atlantic cod]] are usually found between 150 and 200 metres, they are omnivorous and feed on invertebrates and fish, including young cod.<ref>{{fishbase species|genus=Gadus|species=morhua|month=August|year=2009}}</ref> File:Centropristis striata.png| [[Black sea bass]] File:Epinephelus malabaricus.jpg|[[Grouper]] are ambush predators with a powerful sucking system that sucks their prey in from a distance </gallery> {{clear}}

[[Grouper]] are often found around reefs. They have stout bodies and large mouths. They are not built for long-distance or fast swimming. They can be quite large, and lengths over a meter and weights up to 100 kg are not uncommon. They swallow prey rather than biting pieces off it. They do not have many teeth on the edges of their jaws, but they have heavy crushing tooth plates inside the [[pharynx]]. They lie in wait, rather than chasing in open water. They are found in areas of hard or consolidated substrate, and use structural features such as ledges, rocks, and coral reefs (as well as [[artificial reef]]s like wrecks and sunken barges) as their habitat. Their mouth and [[gill]]s form a powerful sucking system that sucks their prey in from a distance. They also use their mouth to dig into sand to form their shelters under big rocks, jetting it out through their gills. Their gill muscles are so powerful that it is nearly impossible to pull them out of their cave if they feel attacked and extend those muscles to lock themselves in. There is some research indicating that roving coral groupers (''Plectropomus pessuliferus'') sometimes cooperate with [[moray eel|giant morays]] in hunting.<ref>{{cite journal|last1=Bshary|first1=Redouan|last2=Hohner|first2=Andrea|last3=Ait-el-Djoudi|first3=Karim|last4=Fricke|first4=Hans|title=Interspecific Communicative and Coordinated Hunting between Groupers and Giant Moray Eels in the Red Sea|journal=PLOS Biology|volume=4|issue=12|pages=e431|doi=10.1371/journal.pbio.0040431|pmid=17147471|pmc=1750927|year=2006 |doi-access=free }}</ref>

<gallery heights="90px" mode="packed" style="float:left;"> File:Toothfish.jpg|The [[Patagonian toothfish]] is a robust benthopelagic fish File:Orange roughy.png|The [[orange roughy]] is also a robust benthopelagic fish File:Macruronus novaezelandiae.jpg|The [[blue grenadier]] (hoki), a deep water demersal fish, is subjected to a large [[sustainable fishing]] industry in New Zealand.<ref name="MSCcertification">{{cite web|url=http://www.msc.org/track-a-fishery/certified/pacific/new-zealand-hoki/meet-the-fishers|title=New Zealand hoki - MSC Fisheries|website=www.msc.org|access-date=2009-08-31|archive-url=https://web.archive.org/web/20090806005306/http://www.msc.org/track-a-fishery/certified/pacific/new-zealand-hoki/meet-the-fishers|archive-date=2009-08-06|url-status=dead}}</ref> </gallery> {{clear}}

Deepwater benthopelagic fish are robust, muscular swimmers that actively cruise the bottom searching for prey. They often live around features, such as [[seamount]]s, which have strong currents.<ref name="Fine"/> Commercial examples are the [[orange roughy]] and [[Patagonian toothfish]]. Because these fish were once abundant, and because their robust bodies are good to eat, these fish have been commercially harvested.<ref>{{FishBase species|genus=Hoplostethus|species=atlanticus|year=2009|month=August}}</ref><ref>{{FishBase species|genus=Dissostichus|species=eleginoides|year=2009|month=August}}</ref>

==Conservation status== {{common fish}}

Major demersal fishery species in the [[North Sea]] such as [[cod]], [[plaice]], [[monkfish]] and [[sole (fish)|sole]], are listed by the [[International Council for the Exploration of the Sea|ICES]] as "outside safe biological limits."

'''The by-catch problem'''

A major problem in conservation of demersal fish populations is that of by-catch, whereby fish are caught by accident when targeting other species. The European Commission has written that “A key issue is that many of the most important demersal stocks (i.e. those that live on or near the bottom of the sea) are caught in mixed fisheries. In practice, this means that each time a vessel retrieves its fishing gear, its catch will consist of a mix of different species.”<ref>{{CELEX|52018PC0149|text=Proposal for a REGULATION OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL establishing a multiannual plan for fish stocks in the Western Waters and adjacent waters, and for fisheries exploiting those stocks, amending Regulation (EU) 2016/1139 establishing a multiannual plan for the Baltic Sea, and repealing Regulations (EC) No 811/2004, (EC) No 2166/2005, (EC) No 388/2006, (EC) 509/2007 and (EC) 1300/2008.}} (Explanatory Memorandum)</ref> This has led to a situation whereby, even when the International Council for the Exploration of the Sea recommends a Total Allowable Catch of zero for a given demersal species in order to allow replenishment of population, the European Council nonetheless sets the Total Allowable Catch far above zero so long as the catch is by-catch, in order not to prevent trawlers fishing for other species.<ref>{{CELEX|62022CJ0330|text=Judgment of the Court (Fifth Chamber) of 11 January 2024. Friends of the Irish Environment CLG v Minister for Agriculture Food and the Marine and Others. Case C-330/22.}}</ref> This means that those threatened species do not get the chance to replenish even when not directly targeted by trawlers.

* The Common Sole, ''[[Solea solea]],'' is sufficiently broadly distributed that it is not considered a threatened species; however, [[overfishing]] in Europe has produced severely diminished populations, with declining catches in many regions. For example, the western [[English Channel]] and [[Irish Sea]] sole fisheries face potential collapse according to data in the UK [[Biodiversity Action Plan]]. * Sole, along with the other major bottom-feeding fish in the North Sea such as cod, monkfish, and plaice, is listed by the [[International Council for the Exploration of the Sea|ICES]] as "outside safe biological limits." Moreover, they are growing less quickly now and are rarely older than six years, although they can reach forty. World stocks of large predatory fish and large ground fish such as sole and flounder were estimated in 2003 to be only about 10% of pre-industrial levels.<ref>Clover, Charles. 2004. ''The End of the Line: How overfishing is changing the world and what we eat''. Ebury Press, London. {{ISBN|0-09-189780-7}}</ref><ref>Myers, Ransom A. and Worm, Boris. "Rapid worldwide depletion of predatory fish communities." ''Nature'' '''423''', 280-283 (15 May 2003).</ref><ref>Dalton, Rex. 2006. "Save the big fish: Targeting of larger fish makes populations prone to collapse." Published online [http://www.nature.com/news/2006/061016/full/061016-8.html]</ref> According to the [[World Wildlife Fund]] in 2006, "of the nine sole stocks, seven are overfished with the status of the remaining two unknown." Data is insufficient to assess the remaining stocks; however, landings for all stocks are at or near historical lows."<ref>{{cite web|url=http://www.panda.org/about_wwf/what_we_do/marine/help/seafood_lovers/fish_dishes/plaice_fillet/european_plaice_and_sole/index.cfm|title=Sustainable seafood: Consumer guides|website=panda.org}}</ref> * World stocks of large predatory fish and large ground fish such as sole and flounder were estimated in 2003 to be only about 10% of pre-industrial levels, largely due to overfishing. Most overfishing is due to the extensive activities of the fishing industry.<ref>Clover, Charles. 2004. ''The End of the Line: How overfishing is changing the world and what we eat''. Ebury Press, London. ISBN</ref><ref>Myers, Ransom A. and Worm, Boris. "Rapid worldwide depletion of predatory fish communities." ''Nature'' '''423''', 280–283 (15 May 2003).</ref><ref>{{cite web|url=http://www.bioedonline.org/news/nature-news/save-big-fish/|last=Dalton|first=Rex|date=2006|title=Save the big fish: Targeting of larger fish makes populations prone to collapse|work=BioEd Online|access-date=26 March 2017|archive-date=27 March 2017|archive-url=https://web.archive.org/web/20170327165926/http://www.bioedonline.org/news/nature-news/save-big-fish/|url-status=dead}}</ref><ref>{{cite journal|doi=10.1038/nature05232|pmid=17051218|title=Fishing elevates variability in the abundance of exploited species|journal=Nature|volume=443|issue=7113|pages=859–62|year=2006|last1=Hsieh|first1=Chih-hao|last2=Reiss|first2=Christian S.|last3=Hunter|first3=John R.|last4=Beddington|first4=John R.|last5=May|first5=Robert M.|last6=Sugihara|first6=George|bibcode=2006Natur.443..859H|s2cid=4398663}}</ref> Current research indicate that the flounder population could be as low as 15 million due to heavy overfishing and industrial pollution along the Gulf of Mexico surrounding the coast of Texas. * [[Seafood Watch]] have placed on their list of seafood that [[sustainability]]-minded consumers should avoid the following demersal fish: [[sturgeon]] (imported wild), [[Chilean seabass]], cod (Atlantic, imported Pacific), [[flounder]] (Atlantic), [[halibut]] (Atlantic), sole (Atlantic), [[grouper]], monkfish, [[orange roughy]], demersal [[shark]], [[Red snapper (fish)|red snapper]] and [[tilapia]] (Asia farmed).<ref name="seafoodwatch">{{cite web|url=http://www.montereybayaquarium.org/cr/SeafoodWatch/web/sfw_factsheet.aspx?gid=39|title=Monterey Bay Aquarium: Seafood Watch Program - All Seafood List|publisher=Monterey Bay Aquarium|access-date=2008-04-17|url-status=dead|archive-url=https://web.archive.org/web/20100706015433/http://www.montereybayaquarium.org/cr/SeafoodWatch/web/sfw_factsheet.aspx?gid=39|archive-date=2010-07-06}}</ref>

==See also== {{Commons|Deep sea fish}} {{Portal|Ecology|Environment|Marine Life}} * {{annotated link|Bottom trawling}} * {{annotated link|Deep sea fish}} * {{annotated link|Whitefish (fisheries term)|Whitefish}}

==Notes== {{reflist|2}}

==References== * Bone Q and Moore RH (2008) [https://books.google.com/books?id=sLoqT_xWaqoC&q=%22Biology+of+fishes%22++Bone+Moore ''Biology of Fishes''] Taylor & Francis Group. {{ISBN|978-0-415-37562-7}} * Merrett NR and Haedrich RL (1997) [https://books.google.com/books?id=T5vzoGNM0AQC&dq=%22Demersal+fish%22+definition&pg=PA36 ''Deep-sea demersal fish and fisheries''] Chapman and Hall. {{ISBN|978-0-412-39410-2}}. * Moyle, PB and Cech, JJ (2004) ''Fishes, An Introduction to Ichthyology.'' 5th Ed, Benjamin Cummings. {{ISBN|978-0-13-100847-2}} * [http://www.frs-scotland.gov.uk/Delivery/standalone.aspx?contentid=311 Demersal fisheries] {{Webarchive|url=https://web.archive.org/web/20060707014645/http://www.frs-scotland.gov.uk/Delivery/standalone.aspx?contentid=311 |date=7 July 2006 }} Fishery Research Services. Retrieved 22 July 2009. * [http://www.jncc.gov.uk/page-2525 Deep water demersal fisheries] {{Webarchive|url=https://web.archive.org/web/20091007225556/http://www.jncc.gov.uk/page-2525 |date=7 October 2009 }} [[Joint Nature Conservation Committee]]. Retrieved 22 July 2009.

== External links == * [https://web.archive.org/web/20070930180809/http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?type=simple%3Bc%3Decfr%3Bcc%3Decfr%3Bsid%3D8f61276f3c17bc9d1ceb08e0ec8da919%3Bregion%3DDIV1%3Bq1%3Dgroundfish%3Brgn%3Ddiv7%3Bview%3Dtext%3Bidno%3D20060406%3Bnode%3D20060406%3A1.0.11 Groundfish retention]

{{DEFAULTSORT:Demersal Fish}} [[Category:Aquatic ecology]] [[Category:Marine biology]] [[Category:Ichthyology]] [[Category:Fishing industry]]