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[[File:Moofushi Kandu fish.jpg|thumb|300px|right|Un [[Banco (pesci)|banco]] di grossi pesci predatori pelagici ([[Caranx melampygus|caranghi a pinne blu]]) circonda un banco di [[Pesce azzurro|pesci azzurri]] ([[Engraulidae|acciughe]]).]]
Si definiscono '''pesci pelagici''' i pesci che vivono nella [[Dominio pelagico|zona pelagica]] degli oceani o dei laghi, ovvero in acque che non sono né vicine al fondo né prossime alla costa, a differenza dei [[Demersale|pesci demersali]], che abitano sul fondo o nelle sue vicinanze, e dei [[pesci di barriera]], associati alle [[Barriera corallina|barriere coralline]].<ref name="Lal8">{{cita libro | autore=Brij V. Lal e Kate Fortune | titolo=The Pacific Islands: An Encyclopedia | url=https://books.google.com/books?id=T5pPpJl8E5wC&pg=PA8 | anno=2000 | editore=University of Hawaii Press | isbn=978-0-8248-2265-1 | p=8}}</ref>
L'ambiente pelagico marino rappresenta il più grande habitat acquatico sulla Terra, occupando 1370 milioni di chilometri cubi ed ospitando l'11% delle specie di [[Pesce|pesci]] conosciute. Gli [[Oceano|oceani]] hanno una profondità media di 4000 metri. Circa il 98% del volume totale dell'acqua si trova sotto i 100 metri di profondità, e il 75% è situato oltre i 1000 metri.<ref name="Moyle585">{{cid|Moyle e Cech, 2004|p. 585}}.</ref>
I pesci pelagici marini si dividono in due categorie principali: pesci costieri e pesci oceanici. I [[Pesci costieri|pesci pelagici costieri]] vivono nelle acque relativamente poco profonde e illuminate dal sole al di sopra della [[piattaforma continentale]], mentre i [[#Pesci oceanici|pesci pelagici oceanici]] abitano le acque profonde e vaste al di là della piattaforma continentale, sebbene possano anche nuotare vicino alla costa.<ref>{{cita libro | curatore=A. H. McLintock | anno=1966 | url=http://www.TeAra.govt.nz/en/1966/fish-marine/page-2 | capitolo=Pelagic | titolo=Te Ara – The Encyclopaedia of New Zealand | accesso=29 settembre 2022}}</ref><ref>{{cita libro | autore=Carl Walrond | url=http://www.teara.govt.nz/EarthSeaAndSky/SeaLife/OceanicFish/1/en | capitolo=Oceanic fish | titolo=Encyclopedia of New Zealand | accesso=29 settembre 2022}}</ref>
La dimensione dei pesci pelagici varia da piccoli [[Pesce azzurro|pesci azzurri]] costieri, come [[Clupeidae|aringhe]] e [[Engraulidae|sardine]], a grandi [[Superpredatore|predatori apicali]] oceanici, come il [[Thunnus thynnus|tonno rosso]] e gli [[Selachimorpha|squali]] oceanici.<ref name="Lal8"/> Solitamente, sono nuotatori agili con corpi idrodinamici, capaci di percorrere lunghe distanze durante le [[Migrazione ittica|migrazioni]]. Molti pesci pelagici nuotano in [[Banco (pesci)|banchi]] che possono pesare centinaia di tonnellate, mentre altri, come il grande [[Mola mola|pesce luna oceanico]], sono solitari.<ref name="Lal8"/> Esistono anche pesci pelagici d'acqua dolce in alcuni grandi laghi, come la [[Limnothrissa miodon|sardina del Lago Tanganica]].<ref>{{cita web | url=http://pcwww.liv.ac.uk/aquabiol/BIOL468/gtlakes/african_gt_lakes/tanganyika/tanganyika_main.htm | titolo=Lake Tanganyika | sito=pcwww.liv.ac.uk}}</ref>
== Pesci epipelagici ==
{{Doppia immagine verticale|destra|Bluefin-big.jpg|Herring2.jpg|220|I grandi pesci predatori epipelagici, come questo [[Thunnus thynnus|tonno rosso]], hanno una coda profondamente biforcuta e un corpo liscio affusolato a entrambe le estremità, con una colorazione controombreggiata e tonalità argentate.|I piccoli [[Pesce azzurro|pesci azzurri]] epipelagici, come questa [[Clupea harengus|aringa]], condividono caratteristiche corporee simili a quelle dei pesci predatori descritti sopra.}}
I pesci epipelagici abitano la [[Zona eufotica|zona epipelagica]], lo strato più superficiale della [[colonna d'acqua]], che va dal [[livello del mare]] fino a 200 metri di profondità. Questa zona, conosciuta anche come «zona superficiale» o «zona illuminata», include la [[Zona eufotica|zona fotica]]. La zona fotica è definita come lo strato d'acqua in cui la luce solare [[Attenuazione|si riduce]] fino all'1% rispetto alla sua intensità superficiale. La profondità di questa zona varia a seconda della [[Turbidimetria|torbidità]] dell'acqua, ma in acque limpide può raggiungere i 200 metri, coincidenti con la zona epipelagica. La luce presente in questa zona permette al [[fitoplancton]] di svolgere la [[Fotosintesi clorofilliana|fotosintesi]].<ref name="Moyle571"/>
La zona epipelagica costituisce un vasto habitat per la maggior parte dei pesci pelagici. È ben illuminata, favorendo i predatori che fanno affidamento sulla vista, ed è generalmente ben mescolata e ossigenata grazie al movimento delle onde, oltre a offrire un ambiente ideale per la crescita delle [[Alga|alghe]]. Tuttavia, questa zona presenta una scarsa varietà di habitat, il che si traduce in una limitata diversità di specie, supportando meno del 2% delle specie ittiche conosciute nel mondo. Inoltre, molte aree di questa zona sono povere di nutrienti necessari per sostenere la vita dei pesci. Per questo motivo, i pesci epipelagici tendono a concentrarsi nelle acque costiere sopra le [[Piattaforma continentale|piattaforme continentali]], dove i nutrienti arrivano tramite il [[ruscellamento]], o nelle zone oceaniche in cui i movimenti di [[Upwelling|risalita]] portano nutrienti in superficie.<ref name="Moyle571">{{cid|Moyle e Cech, 2004|p. 571}}.</ref>
I pesci epipelagici si dividono principalmente in piccoli [[Pesce azzurro|pesci azzurri]] e grandi predatori che si nutrono di essi. I pesci azzurri si riuniscono in [[Banco (pesci)|banchi]] e filtrano il [[plancton]]. La maggior parte dei pesci epipelagici ha corpi idrodinamici, progettati per sostenere lunghe [[Migrazione ittica|migrazioni]]. Predatori e pesci azzurri condividono spesso caratteristiche [[Morfologia (biologia)|morfologiche]] simili. I predatori, di solito fusiformi, possiedono grandi bocche, corpi lisci e code profondamente biforcute. Molti usano la vista per cacciare zooplancton o pesci più piccoli, mentre altri filtrano il plancton dall'acqua.
[[File:Herring Silvering.svg|thumb|160px|left|Le scaglie riflettenti dell'[[Clupeidae|aringa]] sono quasi verticali per garantire un mimetismo laterale.]]
La maggior parte dei pesci predatori epipelagici e delle loro prede più piccole presentano una colorazione controombreggiante, con toni argentei che riducono la visibilità [[Riflessione diffusa|disperdendo]] la luce incidente.<ref name="Moyle571"/> Questo effetto argentato è dovuto a delle [[Scaglia|scaglie]] riflettenti che agiscono come piccoli specchi, creando un effetto di trasparenza. A profondità intermedie, dove la luce proviene dall'alto, questi «specchi» orientati verticalmente rendono i pesci invisibili se visti di lato.<ref name=Herring2002>{{cita libro | autore=Peter Herring | anno=2002 | titolo=The Biology of the Deep Ocean | pp=192-95 | editore=[[Oxford University Press]] | isbn=978-0-19-854956-7}}</ref>
Nelle acque più superficiali, le scaglie devono riflettere una gamma diversa di lunghezze d'onda, e per raggiungere questo scopo sono dotate di cristalli distanziati variabilmente. Nei pesci dal corpo arrotondato, le scaglie riflettenti sono costituite da molteplici piccoli riflettori orientati verticalmente per mantenere l'effetto specchio.<ref name=Herring2002/>
Nonostante il numero limitato di specie, i pesci epipelagici sono estremamente abbondanti. Ciò che manca in diversità è compensato dalla quantità. I pesci azzurri formano banchi enormi, e i grandi predatori che se ne nutrono sono spesso molto ricercati nell'[[Pesce (alimento)|industria alimentare]]. Nell'insieme, i pesci epipelagici rappresentano la risorsa ittica più importante del mondo.<ref name="Moyle571"/>
Molti pesci azzurri sono predatori facoltativi, in grado di catturare singoli [[Copepoda|copepodi]] o avannotti dalla colonna d'acqua, ma anche di passare a un'alimentazione per filtrazione di [[fitoplancton]] quando ciò risulta più vantaggioso in termini energetici. I pesci che si nutrono filtrando utilizzano spesso branchiospine lunghe e sottili per trattenere piccoli organismi dall'acqua. Alcuni dei più grandi pesci epipelagici, come lo [[Cetorhinus maximus|squalo elefante]] e lo [[Rhincodon typus|squalo balena]], sono filtratori, così come alcuni dei più piccoli, come gli [[Sprattus|spratti]] adulti e le [[Engraulidae|acciughe]].<ref name="Moyle572">{{cid|Moyle e Cech, 2004|p. 572}}.</ref>
Le acque oceaniche particolarmente limpide contengono poco cibo. Le aree ad alta produttività tendono a essere leggermente torbide a causa delle [[Fioritura algale|fioriture di plancton]], che attirano i pesci filtratori, seguiti dai predatori più grandi. La pesca del tonno è spesso ottimale in acque con una torbidità tale che un [[disco di Secchi]] sia visibile tra 15 e 35 metri di profondità durante una giornata di sole.<ref>{{cita pubblicazione | autore=Blackburn | anno=1965 | titolo=Oceanography and the ecology of tunas | rivista=Oceanography and Marine Biology: An Annual Review | volume=3 | pp=299-322}}</ref>
===Floating objects===
{{multiple image
| align = left
| direction = vertical
| width = 220
| image1 = Sargassum weeds closeup.jpg
| alt1 =
| caption1 = Drifting ''[[Sargassum]]'' seaweed provides food and shelter for small epipelagic fish. The small round spheres are floats filled with carbon dioxide which provide buoyancy to the algae.
| image2 = Great Barracuda off the Netherland Antilles.jpg
| alt2 =
| caption2 = [[Great barracuda]] accompanied by a school of [[Carangidae|jacks]]
}}
{{multiple image
| align = right
| direction = vertical
| width = 220
| image1 = Lines of sargassum Sargasso Sea.jpg
| alt1 =
| caption1 = Lines of ''Sargassum'' can stretch for miles along the ocean surface.
| image2 = Histrio histrio by A. H. Baldwin.jpg
| alt2 =
| caption2 = The camouflaged [[sargassum fish]] has evolved to live among drifting ''Sargassum'' seaweed.
}}
Epipelagic fish are fascinated by floating objects. They aggregate in considerable numbers around objects such as drifting flotsam, rafts, jellyfish, and floating seaweed. The objects appear to provide a "visual stimulus in an optical void".<ref>{{cite journal|author=Hunter, JR |author2=Mitchell CT |year=1966|title=Association of fishes with flotsam in the offshore waters of Central America|journal=Fishery Bulletin|volume=66|pages=13–29}}</ref> Floating objects may offer [[refuge (ecology)|refuge]] for [[juvenile fish]] from predators. An abundance of drifting seaweed or jellyfish can result in significant increases in the survival rates of some juvenile species.<ref>{{cite journal|author=Kingsford MJ |year=1993|title=Biotic and abiotic structure in the pelagic environment: Importance to small fishes |journal=Bulletin of Marine Science |url=https://www.researchgate.net/publication/233550840|volume=53|issue=2|pages=393–415}}</ref>
Many coastal juveniles use seaweed for the shelter and the food that is available from invertebrates and other fish associated with it. Drifting seaweed, particularly the pelagic ''[[Sargassum]]'', provide a niche habitat with its own shelter and food, and even supports its own unique fauna, such as the [[sargassum fish]].<ref name="Moyle572"/> One study, off Florida, found 54 species from 23 families living in flotsam from ''Sargassum'' mats.<ref>{{cite journal|author=Dooley JK |year=1972|title=Fishes associated with the pelagic sargassum complex, with a discussion of the sargassum community|journal=Contributions in Marine Science|volume=16|pages=1–32}}</ref> Jellyfish also are used by juvenile fish for shelter and food, even though jellyfish can prey on small fish.<ref name="Moyle576">[[#Moyle|Moyle and Cech]], p. 576</ref>
Mobile oceanic species such as [[tuna]] can be captured by travelling long distances in large [[fishing vessel]]s. A simpler alternative is to leverage off the fascination fish have with floating objects. When fishermen use such objects, they are called [[fish aggregating device]]s (FADs). FADs are anchored rafts or objects of any type, floating on the surface or just below it. Fishermen in the Pacific and Indian oceans set up floating FADs, assembled from all sorts of debris, around tropical islands, and then use [[purse seine]]s to capture the fish attracted to them.<ref name="Moyle574/5" />
A study using [[Fisheries acoustics|sonar]] in French Polynesia, found large shoals of juvenile [[bigeye tuna]] and [[yellowfin tuna]] aggregated closest to the devices, 10 to 50 m. Farther out, 50 to 150 m, was a less dense group of larger yellowfin and [[albacore tuna]]. Yet farther out, to 500 m, was a dispersed group of various large adult tuna. The distribution and density of these groups was variable and overlapped. The FADs also were used by other fish, and the aggregations dispersed when it was dark.<ref>{{Cite journal | doi = 10.1016/S0990-7440(00)00051-6| title = Typologie et comportement des agrégations thonières autour de dispositifs de concentration de poissons à partir de prospections acoustiques en Polynésie française| journal = Aquatic Living Resources| volume = 13| issue = 4| pages = 183–192| year = 2000| last1 = Josse | first1 = E. }}</ref>
Larger fish, even predator fish such as the [[great barracuda]], often attract a retinue of small fish that accompany them in a strategically safe way. [[Scuba diving|Skindivers]] who remain for long periods in the water also often attract a retinue of fish, with smaller fishes coming in close and larger fishes observing from a greater distance. [[Marine turtle]]s, functioning as a mobile shelter for small fish, can be impaled accidentally by a swordfish trying to catch the fish.<ref>{{Cite journal | doi = 10.1007/BF00004759| title = Impalement of marine turtles (Reptitia, Chelonia: Cheloniidae and Dermochelyidae) by billfishes (Osteichthyes, Perciformes: Istiophoridae and Xiphiidae)| journal = Environmental Biology of Fishes| volume = 39| pages = 85–96| year = 1994| last1 = Frazier | first1 = J. G. | last2 = Fierstine | first2 = H. L. | last3 = Beavers | first3 = S. C. | last4 = Achaval | first4 = F. | last5 = Suganuma | first5 = H. | last6 = Pitman | first6 = R. L. | last7 = Yamaguchi | first7 = Y. | last8 = Prigioni | first8 = C. M. | s2cid = 23551149}}</ref>
===Coastal fish===
{{main|Coastal fish}}
[[File:Sixfinger threadfin school.jpg|thumb|left|Schooling [[threadfin]], a coastal species]]
[[Coastal fish]] (also called [[neritic]] or inshore fish) inhabit the waters near the [[coast]] and above the [[continental shelf]]. Since the continental shelf is usually less than 200 metres deep, it follows that coastal fish that are not demersal fish, are usually epipelagic fish, inhabiting the sunlit epipelagic zone.<ref name="Moyle585"/>
Coastal epipelagic fish are among the most abundant in the world. They include forage fish as well as the predator fish that feed on them. Forage fish thrive in those inshore waters where high productivity results from the upwelling and shoreline run off of nutrients. Some are partial residents that spawn in streams, estuaries, and bays, but most complete their life cycle in the zone.<ref name="Moyle572"/>
{{clear}}
==Oceanic fish==
[[File:Oceanic divisions.svg|thumb|400px|right|Oceanic fish inhabit the [[oceanic zone]], which is the deep open water which lies beyond the continental shelves.]]
Oceanic fish (also called open ocean or offshore fish) live in the waters that are not above the continental shelf. Oceanic fish can be contrasted with [[coastal fish]], who do live above the continental shelf. However, the two types are not mutually exclusive, since there are no firm boundaries between coastal and ocean regions, and many epipelagic fish move between coastal and oceanic waters, particularly in different stages in their life cycle.<ref name="Moyle572"/>
Oceanic epipelagic fish can be true residents, partial residents, or accidental residents. True residents live their entire life in the open ocean. Only a few species are true residents, such as [[tuna]], [[billfish]], [[flying fish]], [[sauries]], [[Pilot fish|pilotfish]], [[remora]]s, [[dolphinfish]], ocean sharks, and [[ocean sunfish]]. Most of these species migrate back and forth across open oceans, rarely venturing over continental shelves. Some true residents associate with drifting jellyfish or seaweeds.<ref name="Moyle572"/>
Partial residents occur in three groups: species that live in the zone only when they are juveniles (drifting with jellyfish and seaweeds); species that live in the zone only when they are adults (salmon, flying fish, dolphin, and whale sharks); and deep water species that make nightly migrations up into the surface waters (such as the [[lanternfish]]).<ref name="Moyle572"/> Accidental residents occur occasionally when adults and juveniles of species from other environments are carried accidentally into the zone by currents.<ref name="Moyle572"/>
{{clear}}
<gallery class="left" widths="225" heights="187">
File:Sunfish.jpg|The huge [[ocean sunfish]], a true resident of the ocean epipelagic zone, sometimes drifts with the current, eating [[jellyfish]].
File:Whale shark Georgia aquarium.jpg|The giant [[whale shark]], another resident of the ocean epipelagic zone, filter feeds on [[plankton]], and periodically dives deep into the mesopelagic zone.
File:Protomyctophum subparallelum (no common name).gif|[[Lanternfish]] are partial residents of the ocean epipelagic zone During the day they hide in deep waters, but at night they migrate up to surface waters to feed.
</gallery>
===Deep water fish===
[[File:Pelagiczone.svg|thumb|160px|right|Scale diagram of the layers of the pelagic zone]]
{{See also|Deep sea fish}}
In the deep ocean, the waters extend far below the epipelagic zone and support very different types of pelagic fishes adapted to living in these deeper zones.<ref name="Moyle585"/>
In deep water, [[marine snow]] is a continuous shower of mostly organic [[detritus]] falling from the upper layers of the water column. Its origin lies in activities within the productive [[photic zone]]. Marine snow includes dead or dying [[plankton]], [[protist]]s ([[diatom]]s), fecal matter, sand, soot, and other inorganic dust. The "snowflakes" grow over time and may reach several centimetres in diameter, travelling for weeks before reaching the ocean floor. However, most organic components of marine snow are consumed by [[microbe]]s, [[zooplankton]], and other filter feeding animals within the first 1,000 metres of their journey, that is, within the epipelagic zone. In this way marine snow can be considered the foundation of deep-sea [[mesopelagic]] and [[benthic]] [[ecosystem]]s: As sunlight cannot reach them, deep-sea organisms rely heavily on marine snow as an energy source.
Some deep-sea pelagic groups, such as the [[lanternfish]], [[ridgehead]], [[marine hatchetfish]], and [[Phosichthyidae|lightfish]] families are sometimes termed ''pseudoceanic'' because, rather than having an even distribution in open water, they occur in significantly higher abundances around structural oases, notably [[seamount]]s, and over [[continental slope]]s. The phenomenon is explained by the likewise abundance of prey species that also are attracted to the structures.
The fish in the different pelagic and deep water benthic zones are physically structured, and behave, in ways that differ markedly from each other. Groups of coexisting species within each zone all seem to operate in similar ways, such as the small mesopelagic [[Diel vertical migration|vertically migrating]] plankton-feeders, the bathypelagic [[anglerfish]]es, and the deep water benthic [[rattail]]s.<ref name="Moyle591">[[#Moyle|Moyle and Cech]], p. 591</ref>
[[Acanthopterygii|Ray finned]] species, with spiny fins, are rare among deep sea fishes, which suggests that deep sea fish are ancient and so well adapted to their environment that invasions by more modern fishes have been unsuccessful.<ref name="Haedrich1996"/> The few ray fins that do exist are mainly in the [[Beryciformes]] and [[Lampriformes]], which also are ancient forms. Most deep sea pelagic fishes belong to their own orders, suggesting a long evolution in deep sea environments. In contrast, deep water benthic species are in orders that include many related shallow water fishes.<ref name="Moyle586">[[#Moyle|Moyle and Cech]], p. 586</ref>
Many species move daily between zones in vertical migrations. In the following table, they are listed in the middle or deeper zone where they regularly are found.
{| class="wikitable"
|+ Species by pelagic zone
|-
! Zone
! Species and species groups include:
|-
| Epipelagic<ref name="Moyle571"/>
|
* [[mackerel shark|mackerel]], [[requiem shark|requiem]] and [[whale shark]]s
* [[clupeiform]]s – [[herring]], [[anchovy]]
* [[Salmonidae]] – [[salmon]]
* [[atheriniform]]s – [[flyingfish]]es, [[halfbeak]]s, [[sauries]]
* [[perciform]]s – [[Carangidae|jacks]], [[dolphinfish]], [[pomfret]]s, [[barracuda]]s, [[tuna]]s, [[billfish]].
|-
| Mesopelagic
| [[Lanternfish]], [[opah]], [[longnose lancetfish]], [[barreleye]], [[ridgehead]], [[sabertooth fish|sabretooth]], [[stoplight loosejaw]], [[marine hatchetfish]]<ref>{{fishbase species |genus=Argyropelecus|species=aculeatus |month=August |year=2009}}</ref>
|-
| Bathypelagic
| Principally [[bristlemouth]] and [[anglerfish]]. Also [[fangtooth]], [[viperfish]], [[black swallower]], [[telescopefish]], [[hammerjaw]], [[daggertooth]], [[barracudina]], [[black scabbardfish]], [[bobtail snipe eel]], [[unicorn crestfish]], [[Saccopharynx|gulper eel]], [[flabby whalefish]].
|-
| Benthopelagic<ref name="Moyle571"/>
| [[Rattail]] and [[Ophidiidae|brotula]] are particularly abundant.
|-
| Benthic
| [[Flatfish]], [[hagfish]], [[eelpout]], [[greeneye]] [[eel]], [[stingray]], [[lumpfish]], and [[Pancake batfish|batfish]]<ref name="Moyle571"/>
|}
{| class="wikitable"
|+ '''Comparative structure of pelagic fishes'''
|-
!
! Epipelagic
! Mesopelagic
! Bathypelagic
! Deep sea [[benthic]]
|-
| muscles
|
| muscular bodies
| poorly developed, flabby
|
|-
| skeleton
|
| strong, ossified bones
| weak, minimal ossification
|
|-
| scales
|
| yes
| none
|
|-
| nervous systems
|
| well developed
| lateral line and olfactory only
|
|-
| eyes
|
| large and sensitive
| small and may not function
| variable (well developed to absent)
|-
| photophores
| absent
| common
| common
| usually absent
|-
| gills
|
| well developed
|
|
|-
| kidneys
|
| large
| small
|
|-
| heart
|
| large
| small
|
|-
| swimbladder
|
| vertically migratory fish have swimbladders
| reduced or absent
| variable (well developed to absent)
|-
| size
|
|
| usually under 25 cm
| variable, species greater than one metre are not uncommon
|}
===Mesopelagic fish===
[[File:california headlightfish.png|thumb|Most mesopelagic fishes are small filter feeders that ascend at night to feed in the nutrient rich waters of the epipelagic zone. During the day, they return to the dark, cold, oxygen-deficient waters of the mesopelagic where they are relatively safe from predators. [[Lanternfish]] account for as much as 65% of all deep sea fish [[biomass]] and are largely responsible for the [[deep scattering layer]] of the world's oceans.]]
[[File:Coccorella atrata.png|thumb|Most of the rest of the mesopelagic fishes are ambush predators, such as this [[sabertooth fish]]. The sabertooth uses its telescopic, upward-pointing eyes to pick out prey silhouetted against the gloom above. Their recurved teeth prevent a captured fish from backing out.]]
Below the epipelagic zone, conditions change rapidly. Between 200 metres and approximately 1000 metres, light continues to fade until darkness is nearly complete. Temperatures fall through a [[thermocline]] to temperatures between {{convert|4|°C|°F}} and {{convert|8|°C|°F}}. This is the twilight or [[mesopelagic]] zone. Pressure continues to increase, at the rate of one atmosphere every 10 metres, while nutrient concentrations fall, along with dissolved oxygen and the rate at which the water circulates.<ref name="Moyle585"/><ref name="salvanes2001" />
Sonar operators, using the sonar technology developed during World War II, were puzzled by what appeared to be a false sea floor 300–500 metres deep at day, and less deep at night. This turned out to be due to millions of marine organisms, most particularly small mesopelagic fish, with swimbladders that reflected the sonar.
Mesopelagic organisms migrate into shallower water at dusk to feed on plankton. The layer is deeper when the moon is out, and may move higher when the sky is dark. This phenomenon has come to be known as the [[deep scattering layer]].<ref name="TeAraMZ">Ryan P [http://www.teara.govt.nz/EarthSeaAndSky/SeaLife/DeepSeaCreatures/2/en "Deep-sea creatures: The mesopelagic zone"] ''Te Ara – the Encyclopedia of New Zealand''. Updated 21 September 2007.</ref>
Most mesopelagic fish make [[Diel vertical migration|daily vertical migrations]], moving each night into the epipelagic zone, often following similar migrations of zooplankton, and returning to the depths for safety during the day.<ref name="salvanes2001" /><ref name="Moyle585" /><ref>[[#Bone|Bone and Moore]], p. 38.</ref> These vertical migrations occur over hundreds of meters.
These fish have muscular bodies, ossified bones, scales, well developed gills and central nervous systems, and large hearts and kidneys. Mesopelagic [[Filter feeder|plankton feeders]] have small mouths with fine [[gill raker]]s, while the [[piscivore]]s have larger mouths and coarser gill rakers.<ref name="salvanes2001">{{cite journal |title=Mesopelagic Fishes |journal=Encyclopedia of Ocean Sciences |year=2001 |last1=Salvanes |first1=A.G.V. |last2=Kristoffersen |first2=J.B. |volume=3 |url=http://earthguide.ucsd.edu/fishes/environment/0_images/Original/myctophids/salvanes_01.pdf |access-date=4 November 2020 }}</ref><ref name="Moyle585" />
Vertically migratory fish have [[swimbladder]]s.<ref name="Haedrich1996">{{Cite journal | doi = 10.1111/j.1095-8649.1996.tb06066.x| title = Deep-water fishes: Evolution and adaptation in the earth's largest living spaces| journal = Journal of Fish Biology| volume = 49| pages = 40–53| year = 1996| last1 = Haedrich | first1 = R. L.}}
</ref> The fish inflates its swimbladder to move up. Given the high pressures in the mesopelagic zone, this requires significant energy. As the fish ascends, the air in the swimbladder must decrease to prevent the swimbladder from bursting. To return to the depths, the swimbladder is deflated.<ref>{{Cite journal |last1=Douglas |first1=E. |last2=Friedl |first2=W. |last3=Pickwell |first3=G. |year=1976 |title=Fishes in oxygen-minimum zones: Blood oxygenation characteristics |journal=[[Science (journal)|Science]] |volume=191 |issue=4230 |pages=957–9 |bibcode=1976Sci...191..957D |doi=10.1126/science.1251208 |pmid=1251208}}</ref> The migration takes them through the [[thermocline]], where the temperature changes between 10 and 20 °C, thus displaying considerable temperature tolerance.<ref name="Moyle590">[[Pelagic fish#Moyle|Moyle and Cech]], p. 590</ref>
Mesopelagic fish are adapted for an active life under low light conditions. Most of them are visual predators with large eyes. Some of the deeper water fish such as the [[Telescopefish]] have tubular eyes with big lenses and only [[rod cell]]s that look upward. These give binocular vision and great sensitivity to small light signals.<ref name="Moyle585" /> This adaptation gives improved terminal vision at the expense of lateral vision, and allows the predator to pick out [[squid]], [[cuttlefish]], and smaller fish that are silhouetted above them.<ref name="salvanes2001" />
Mesopelagic fish usually lack defensive spines, and use colour for [[camouflage]].<ref name="salvanes2001" /> [[Ambush predator]]s are dark, black or red. Since the longer, red, wavelengths of light do not reach the deep sea, red effectively functions the same as black. Migratory forms use [[Countershading|countershaded]] silvery colours. On their bellies, they often display [[photophore]]s producing low grade light. For a predator from below, looking upward, this [[bioluminescence]] camouflages the silhouette of the fish. However, some of these predators have yellow lenses that filter the (red deficient) ambient light, leaving the bioluminescence visible.<ref>{{Cite journal | doi = 10.1017/S0025315400021019| title = On yellow lenses in mesopelagic animals| journal = Journal of the Marine Biological Association of the United Kingdom| volume = 56| issue = 4| pages = 963–976| year = 2009| last1 = Muntz | first1 = W. R. A. | s2cid = 86353657}}</ref>
<gallery class="left" widths="200px" heights="175px">
File:Dmawsoni Head shot.jpg|The [[Antarctic toothfish]] have large, upward looking eyes, adapted to detecting the silhouettes of prey fish.<ref>{{FishBase species|genus=Dissostichus|species=mawsoni|year=2009|month=August}}</ref>
File:Opisthoproctus soleatus.png|The [[Barreleye]] has barrel-shaped, tubular [[eye]]s that generally are directed upward, but may be swivelled forward.<ref>[https://www.sciencedaily.com/releases/2009/02/090223150331.htm Mystery Of Deep-sea Fish With Tubular Eyes And Transparent Head Solved] ''ScienceDaily'', 24 February 2009.</ref>
Image:Malacosteus niger.jpg|The [[stoplight loosejaw]] has a [[lower jaw]] one-quarter as long as its body. The jaw has no floor and is attached only by a hinge and a modified tongue bone. Large fang-like teeth in the front are followed by many small barbed teeth.<ref name="kenaley">{{cite journal|author=Kenaley, C.P|title=Revision of the Stoplight Loosejaw Genus ''Malacosteus'' (Teleostei: Stomiidae: Malacosteinae), with Description of a New Species from the Temperate Southern Hemisphere and Indian Ocean|journal=Copeia|volume=2007|issue=4|pages=886–900|year=2007|doi=10.1643/0045-8511(2007)7[886:ROTSLG]2.0.CO;2|s2cid=1038874 }}</ref><ref name="sutton">{{cite journal|author=Sutton, T.T.|title=Trophic ecology of the deep-sea fish ''Malacosteus niger'' (Pisces: Stomiidae): An enigmatic feeding ecology to facilitate a unique visual system?|journal=Deep-Sea Research Part I: Oceanographic Research Papers|volume=52|issue=11|date=Nov 2005|pages=2065–2076|doi=10.1016/j.dsr.2005.06.011|bibcode=2005DSRI...52.2065S|url=https://nsuworks.nova.edu/occ_facpresentations/244}}</ref>
Image:Malacosteus.JPG|The [[stoplight loosejaw]] is also one of the few fishes that produce red [[bioluminescence]]. As most of their prey cannot perceive red light, this allows it to hunt with an essentially invisible beam of light.<ref name="kenaley"/>
</gallery>
The [[brownsnout spookfish]] is a species of [[barreleye]] and is the only vertebrate known to employ a mirror, as opposed to a lens, to focus an image in its eyes.<ref name="wagner et al">{{cite journal |author=Wagner, H.J., Douglas, R.H., Frank, T.M., Roberts, N.W., and Partridge, J.C. |title=A Novel Vertebrate Eye Using Both Refractive and Reflective Optics |journal=Current Biology |volume=19 |pages=108–114 |date=27 January 2009 | pmid = 19110427 | doi = 10.1016/j.cub.2008.11.061 |issue=2
|s2cid=18680315 |doi-access=free }}</ref><ref name="smith">Smith, L. (8 January 2009). [https://web.archive.org/web/20110629123143/http://www.timesonline.co.uk/tol/news/environment/article5469077.ece "Fish with four eyes can see through the deep sea gloom"]. ''Times Online''. Times Newspapers Ltd. Retrieved 14 March 2009.</ref>
Sampling via deep [[trawling]] indicates that [[lanternfish]] account for as much as 65% of all deep sea fish [[biomass]].<ref name=EoF>{{cite book |editor=Paxton, J.R. |editor2=Eschmeyer, W.N.|author= Hulley, P. Alexander|year=1998|title=Encyclopedia of Fishes|publisher= Academic Press|___location=San Diego|pages= 127–128|isbn= 978-0-12-547665-2}}</ref> Indeed, lanternfish are among the most widely distributed, populous, and diverse of all [[vertebrate]]s, playing an important [[ecology|ecological]] role as prey for larger organisms. The estimated global biomass of lanternfish is 550–660 million [[tonne]]s, several times the entire world fisheries catch. Lanternfish also account for much of the biomass responsible for the [[deep scattering layer]] of the world's oceans. [[Sonar]] reflects off the millions of lanternfish [[swim bladder]]s, giving the appearance of a false bottom.<ref>{{cite web | title = Deep-sea fish diversity and ecology in the benthic boundary layer |author1=Cornejo, R. |author2=Koppelmann, R. |author3=Sutton, T. |name-list-style=amp |year=2006 | url = http://www.agu.org/meetings/os06/os06-sessions/os06_OS45Q.html}}</ref>
The 2010 Malaspina Circumnavigation Expedition traveled 60,000 km, undertaking acoustic observations. It reported that mesopelagic biomass was 10 billion tonnes or more (10x prior estimates), comprising about 90 percent of all ocean fish biomass.<ref>{{Cite journal |last=Duarte |first=Carlos M. |date=2015-01-28 |title=Seafaring in the 21St Century: The Malaspina 2010 Circumnavigation Expedition |url=http://dx.doi.org/10.1002/lob.10008 |journal=Limnology and Oceanography Bulletin |volume=24 |issue=1 |pages=11–14 |doi=10.1002/lob.10008 |issn=1539-607X|hdl=10754/347123 |hdl-access=free }}</ref> Estimates of how much carbon these fish sequester remained highly uncertain as of 2024.<ref name=":0">{{Cite web |last=Donovan |first=Moira |date=November 21, 2023 |title=All the Fish We Cannot See |url=https://hakaimagazine.com/features/all-the-fish-we-cannot-see/ |access-date=2024-02-19 |website=Hakai Magazine |language=en}}</ref>
Mesopelagic fish do not constitute a major fishery as of 2024. Initial efforts in Iceland, Norway, and the Soviet Union did not create a commercial industry. The European Union funded the MEESO project to study abundance and fishing technologies for key mesopelagic species. To date, fish that appeal to the human palate have not been identified, leading harvesters to focus on animal feed markets instead.<ref name=":0" />
[[Bigeye tuna]] are an epipelagic/mesopelagic species that is carnivorous, eating other fish. Satellite tagging has shown that bigeye tuna often spend prolonged periods cruising deep below the surface during the daytime, sometimes making dives as deep as {{Convert|500|m|ft|abbr=off}}. These movements are thought to be in response to the vertical migrations of prey organisms in the [[deep scattering layer]].
<gallery class="left" widths="187px" heights="167px">
File:Longnoselancetfish.jpg|[[Longnose lancetfish]]. Lancetfish are ambush predators that frequent the mesopelagic. They are among the largest mesopelagic fishes (up to 2 metres).<ref name="Moyle336">[[#Moyle|Moyle and Cech]], p. 336</ref>
File:gigantura chuni.png|The [[telescopefish]] has large, forward-pointing telescoping eyes with large lenses.<ref>{{FishBase species|genus=Gigantura|species=chuni|year=2010|month=October}}</ref>
File:Daggertooth.PNG|The [[daggertooth]] slashes other mesopelagic fish when it bites them with its dagger-like teeth.<ref>{{FishBase species|genus=Anotopterus|species=pharao|year=2010|month=April}}</ref>
File:Thobe u0.gif|[[Bigeye tuna]] cruise the epipelagic zone at night and the mesopelagic zone during the day.
File:Lestidiops affinis (1).jpg|A collection of mesopelagic forage fishes trawled from the Gulf of Mexico that includes [[Myctophids]], larval [[anglerfishes]], [[bristlemouth]]s, and a [[barracudina]]
</gallery>
===Bathypelagic fish===
[[File:Humpback anglerfish.png|thumb|right|The [[humpback anglerfish]] is a bathypelagic ambush predator, which attracts prey with a bioluminescent lure. It can ingest prey larger than itself, which it swallows with an inrush of water when it opens its mouth.<ref name="TeAraBZ" />]]
[[File:Gonostoma bathyphilum.jpg|thumb|right|Many [[bristlemouth]] species, such as the "spark anglemouth" above,<ref>{{FishBase species | genus = Gonostoma | species = bathyphilum | month = January | year = 2006}}</ref> are also bathypelagic ambush predators that can swallow prey larger than themselves. They are among the most abundant of all vertebrate families.<ref>{{FishBase family | family = Gonostoma | month = August | year = 2009}}</ref>]]
[[File:Flabby whalefish.jpg|thumb|right|Young, red [[flabby whalefish]] make nightly vertical migrations into the lower mesopelagic zone to feed on [[copepods]]. When males mature into adults, they develop a massive liver and then their jaws fuse shut. They no longer eat, but continue to metabolise the energy stored in their liver.<ref name="aparticle">{{cite web |url=https://www.nbcnews.com/id/wbna28801960 |title=Scientists solve mystery: 3 fish are all the same |date=22 January 2009 |author=Schmid, Randolph E. |publisher=Associated Press}}</ref>]]
Below the mesopelagic zone it is pitch dark. This is the '''midnight''' or [[bathypelagic zone]], extending from 1000 m to the bottom deep water [[benthic zone]]. If the water is exceptionally deep, the pelagic zone below {{Convert|4000|m|mi|abbr=off}} sometimes is called the '''lower midnight''' or [[abyssopelagic zone]].
Conditions are somewhat uniform throughout these zones, the darkness is complete, the pressure is crushing, and temperatures, nutrients, and dissolved oxygen levels are all low.<ref name="Moyle585"/>
Bathypelagic fish have special [[adaptation]]s to cope with these conditions – they have slow [[metabolism]]s and unspecialized diets, being willing to eat anything that comes along. They prefer to sit and wait for food rather than waste energy searching for it. The behaviour of bathypelagic fish can be contrasted with the behaviour of mesopelagic fish. Mesopelagic are often highly mobile, whereas bathypelagic fish are almost all lie-in-wait predators, normally expending little energy in movement.<ref name="Moyle594">[[#Moyle|Moyle and Cech]], p. 594</ref>
The dominant bathypelagic fishes are small [[bristlemouth]] and [[anglerfish]]; [[fangtooth]], [[viperfish]], [[daggertooth]], and [[barracudina]] are also common. These fishes are small, many about {{Convert|10|cm|in|abbr=off}} long, and not many longer than {{Convert|25|cm|in|abbr=on}}. They spend most of their time waiting patiently in the water column for prey to appear or to be lured by their phosphors. What little energy is available in the bathypelagic zone filters from above in the form of detritus, faecal material, and the occasional invertebrate or mesopelagic fish.<ref name="Moyle594"/> About 20% of the food that has its origins in the epipelagic zone falls down to the mesopelagic zone,<ref name="TeAraMZ" /> but only about 5% filters down to the bathypelagic zone.<ref name="TeAraBZ">Ryan P [http://www.teara.govt.nz/EarthSeaAndSky/SeaLife/DeepSeaCreatures/3/en "Deep-sea creatures: The bathypelagic zone"] ''Te Ara – the Encyclopedia of New Zealand''. Updated 21 September 2007.</ref>
Bathypelagic fish are sedentary, adapted to outputting minimum energy in a habitat with very little food or available energy, not even sunlight, only bioluminescence. Their bodies are [[wiktionary:elongate|elongated]] with weak, watery muscles and [[skeleton|skeletal]] structures. Since so much of the fish is water, they are not compressed by the great pressures at these depths. They often have extensible, hinged [[Jaw#The jaw in fish|jaws]] with recurved teeth. They are slimy, without [[Fish scale|scale]]s. The central nervous system is confined to the lateral line and olfactory systems, the eyes are small and may not function, and [[gill]]s, kidneys and hearts, and [[swimbladder]]s are small or missing.<ref name="TeAraBZ" /><ref name="Moyle587">[[#Moyle|Moyle and Cech]], p. 587</ref>
These are the same features found in fish [[larvae]], which suggests that during their evolution, bathypelagic fish have acquired these features through [[neoteny]]. As with larvae, these features allow the fish to remain suspended in the water with little expenditure of energy.<ref>Marshall (1984) "Progenetic tendencies in deep-sea fishes", pp. 91–101 in Potts GW and Wootton RJ (eds.) (1984) ''Fish reproduction: strategies and tactics'' Fisheries Society of the British Isles.</ref>
Despite their ferocious appearance, these beasts of the deep are mostly miniature fish with weak muscles, and are too small to represent any threat to humans.
The swimbladders of deep sea fish are either absent or scarcely operational, and bathypelagic fish do not normally undertake vertical migrations. Filling bladders at such great pressures incurs huge energy costs. Some deep sea fishes have swimbladders that function while they are young and inhabit the upper epipelagic zone, but they wither or fill with fat when the fish move down to their adult habitat.<ref>{{cite journal|author=Horn MH |year=1970|url=http://biostor.org/reference/4182 |title=The swimbladder as a juvenile organ in stromateoid fishes|journal=Breviora|volume=359|pages=1–9}}</ref>
The most important sensory systems are usually the [[inner ear]], which responds to sound, and the [[lateral line]], which responds to changes in water pressure. The [[olfactory]] system also can be important for males who find females by smell.<ref>{{Cite journal | doi = 10.1086/285295|jstor=2462555| title = Location by Olfaction: A Model and Application to the Mating Problem in the Deep-Sea Hatchetfish ''Argyropelecus hemigymnus''| journal = The American Naturalist| volume = 138| issue = 6| pages = 1431| year = 1991| last1 = Jumper | first1 = J. | last2 = Baird | first2 = R. C. |s2cid=84386858 }}</ref>
Bathypelagic fish are black, or sometimes red, with few [[photophore]]s. When photophores are used, it is usually to entice prey or attract a mate. Because food is so scarce, bathypelagic predators are not selective in their feeding habits, but grab whatever comes close enough. They accomplish this by having a large mouth with sharp teeth for grabbing large prey and overlapping [[gill raker]]s that prevent small prey that have been swallowed from escaping.<ref name="Moyle587"/>
It is not easy finding a mate in this zone. Some species depend on [[bioluminescence]]. Others are [[hermaphrodite]]s, which doubles their chances of producing both eggs and sperm when an encounter occurs.<ref name="TeAraBZ" /> The female anglerfish releases [[pheromone]]s to attract tiny males. When a male finds her, he bites onto her and never lets go. When a male of the anglerfish species ''[[Haplophryne mollis]]'' bites into the skin of a female, he release an [[enzyme]] that digests the skin of his mouth and her body, fusing the pair to the point where the two circulatory systems join up. The male then atrophies into nothing more than a pair of [[gonads]]. This extreme [[sexual dimorphism]] ensures that, when the female is ready to spawn, she has a mate immediately available.<ref name="doran">{{Cite journal | doi = 10.1038/256038a0| title = Precocious sexual parasitism in the deep sea ceratioid anglerfish, ''Cryptopsaras couesi'' Gill| journal = Nature| volume = 256| issue = 5512| pages = 38–40| year = 1975| last1 = Pietsch | first1 = T. W. | bibcode = 1975Natur.256...38P| s2cid = 4226567}}</ref>
Many animal forms other than fish live in the bathypelagic zone, such as squid, large whales, octopuses, sponges, [[brachiopod]]s, sea stars, and [[echinoid]]s, but this zone is difficult for fish to live in.
<gallery class="left" widths="187px" heights="167px">
File:Eurypharynx pelecanoides.jpg|The [[Saccopharynx|gulper eel]] uses its mouth like a net by opening its large mouth and swimming at its prey. It has a luminescent organ at the tip of its tail to attract prey.
Image:Chiasmodon niger.jpg|The [[black swallower]], with its distensible stomach, is notable for its ability to swallow whole [[bony fish]]es ten times its mass.<ref name="jordan">{{cite book|title=A Guide to the Study of Fishes|url=https://archive.org/details/aguidetostudyfi02jordgoog|author=Jordan, D.S.|publisher=H. Holt and Company|year=1905}}</ref><ref>{{fishbase species|genus=Chiasmodon|species=niger|year=2009|month=August}}</ref>
Image:Hamol u0.gif|Female ''[[Haplophryne mollis]]'' anglerfish trailing attached males that have atrophied into a pair of [[gonads]], for use when the female is ready to spawn.
File:Anoplogaster cornuta 2.jpg|The widespread [[fangtooth]] has the largest teeth of any fish, proportionate to body size.<ref>{{FishBase species|genus = Anoplogaster|species = cornuta|month = August|year = 2009}}</ref> Despite their ferocious appearance, bathypelagic fish are usually weakly muscled and too small to represent any threat to humans.
File:Messina Straits Chauliodus sloani.jpg|The [[Sloane's viperfish]] can make nightly migrations from bathypelagic depths to near surface waters.<ref>{{FishBase species|genus= Chauliodus|species= sloani|year= 2010|month= April}}</ref>
</gallery>
==Demersal fish==
[[File:Giant grenadier.jpg|thumb|right|[[Giant grenadier]], an [[wiktionary:elongate|elongate]] benthic fish with large eyes and well-developed [[lateral line]]s]]
{{See also|Demersal fish}}
[[Demersal fish]] live on or near the bottom of the sea.<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> Demersal fish are found by the [[seafloor]] in coastal areas on the [[continental shelf]], and in the open ocean they are found along the outer [[continental margin]] on the continental slope and the continental rise. They are not generally found at [[abyssopelagic]] or [[hadopelagic]] depths or on the [[abyssal plain]]. They occupy a range of seafloors consisting of mud, sand, gravel, or rocks.<ref name="seafloor" />
In deep waters, the fishes of the demersal zone are active and relatively abundant, compared to fishes of the [[bathypelagic zone]].<ref name="Moyle594"/>
[[Rattail]]s and [[Ophidiidae|brotula]]s are common, and other well-established families are [[eel]]s, [[eelpout]]s, [[hagfish]]es, [[greeneye]]s, [[Pancake batfish|batfish]]es, and [[lumpfish]]es.<ref name="Moyle587"/>
The bodies of deep water [[benthic]] fishes are muscular with well developed organs. In this way they are closer to mesopelagic fishes than bathopelagic fishes. 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, with larger species greater than one metre not uncommon.
Deep sea benthic fish are usually long and narrow. Many are eels or shaped like eels. This may be because long bodies have long [[lateral line]]s. Lateral lines detect low-frequency sounds, and some benthic fishes appear to have muscles that drum such sounds to attract mates.<ref name="Haedrich1996"/> Smell is also important, as indicated by the rapidity with which benthic fish find traps baited with [[bait fish]].
The main diet of deep sea benthic fish is invertebrates 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|Moyle and Cech]], p. 588</ref>
Deep sea benthic fish can be divided into strictly benthic fish and benthopelagic fish. Usually, strictly benthic fish are negatively buoyant, while benthopelagic fish are neutrally buoyant. Strictly benthic fish stay in constant contact with the bottom. They either lie in wait as [[ambush predator]]s or move actively over the bottom in search for food.<ref name="Moyle588"/>
[[File:Orange roughy.png|thumb|right|[[Orange roughy]]]]
[[File:Toothfish.jpg|thumb|right|[[Patagonian toothfish]]]]
===Benthopelagic fish===
{{See also|Benthopelagic fish}}
Benthopelagic fish inhabit the water just above the bottom, feeding on [[benthos]] and benthopelagic [[zooplankton]].<ref>{{cite journal|author=Mauchline J |author2= Gordon JDM |year=1986|title=Foraging strategies of deep-sea fish|journal=Mar. Ecol. Prog. Ser.|volume=27|pages=227–238|doi=10.3354/meps027227|bibcode=1986MEPS...27..227M|doi-access=free}}</ref> Most dermersal fish are benthopelagic.<ref name="seafloor" />
They can be divided into flabby or robust body types. Flabby benthopelagic fishes are like bathopelagic fishes, they have a reduced body mass, and low metabolic rates, expending minimal energy as they lie and wait to [[Ambush predator|ambush]] prey.<ref>{{Cite journal | doi = 10.1111/j.1095-8649.1996.tb06067.x| title = Energetic and life-history patterns of deep-sea benthic, benthopelagic and seamount-associated fish| journal = Journal of Fish Biology| volume = 49| pages = 54–74| year = 1996| last1 = Koslow | first1 = J. A.}}</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% 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">{{Cite journal | doi = 10.1098/rspb.1987.0018|pmid=2884671|jstor=36061|url=https://www.researchgate.net/publication/20270929| title = ''Acanthonus armatus'', a Deep-Sea Teleost Fish with a Minute Brain and Large Ears| journal = Proceedings of the Royal Society B: Biological Sciences| volume = 230| issue = 1259| pages = 257–65| year = 1987| last1 = Fine | first1 = M. L.| last2 = Horn | first2 = M. H.| last3 = Cox | first3 = B.|bibcode=1987RSPSB.230..257F|s2cid=19183523}}</ref>
Robust benthopelagic fish are muscular swimmers that actively cruise the bottom searching for prey. They may live around features, such as [[seamount]]s, which have strong currents.<ref name="Fine"/> 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 harvested commercially.<ref>{{FishBase species|genus=Hoplostethus|species=atlanticus|year=2009|month=August}}</ref><ref>{{FishBase species|genus=Dissostichus|species=eleginoides|year=2009|month=August}}</ref>
===Benthic fish===
{{See also|Benthic fish}}
Benthic fish are not pelagic fish, but they are discussed here briefly, by way of completeness and contrast.
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>{{cite journal|author= Sulak KJ |title=The systematics and biology of ''Bathypterois'' (Pisces, Chlorophthalmidae) with a revised classification of benthic myctophiform fishes|journal= Galathea Rep.|volume= 14|url=https://www.researchgate.net/publication/237671743}}</ref>
The deepest-living fish known, the strictly benthic ''[[Abyssobrotula galatheae]]'', eel-like and blind, feeds on benthic invertebrates.<ref>{{cite journal|author=Nielsen JG |year=1977|title=The deepest living fish ''Abyssobrotula galatheae'': a new genus and species of oviparous ophidioids (Pisces, Brotulidae)|journal=Galathea Report|volume=14|pages=41–48|url=http://bionames.org/references/7b623b8692cc9de5ca095628affbc735}}</ref><ref>{{fishbase species |genus=Abyssobrotula |species=galatheae |month=August |year=2009}}</ref>
<gallery class="left" widths="200" heights="175">
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:Taeniura meyeni reef.jpg|The [[blotched fantail ray]] feeds on bottom-dwelling fish, bivalves, crabs, and shrimps.<ref>{{fishbase species|genus=Taeniura|species=meyeni|month=August|year=2009}}</ref>
</gallery>
[[File:Oceanic basin.svg|thumb|Cross-section of an ocean basin, note significant [[vertical exaggeration]]]]
At great depths, food scarcity and extreme pressure works to limit the survivability of fish. The deepest point of the ocean is about {{Convert|11000|m|mi|abbr=off}}. Bathypelagic fishes are not normally found below {{Convert|3000|m|mi|abbr=off}}. The greatest depth recorded for a benthic fish is {{Convert|8370|m|mi|abbr=on}}.<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" />
Benthic fishes are more diverse and are likely to be found on the [[continental slope]], where there is habitat diversity and often, food supplies. Approximately 40% of the ocean floor consists of [[abyssal plain]]s, but these flat, featureless regions are covered with [[Pelagic sediments|sediment]] and 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 that support benthic fish. Undersea mountain ranges may separate underwater regions into different ecosystems.<ref name="Moyle591" />
{{clear}}
==Pelagic fisheries==
===Forage fish===
{{marine wild fish taxa}}
{{See also|Forage fish}}
Small pelagic fish are usually [[forage fish]] that are hunted by larger pelagic fish and other predators. Forage fish [[Filter feeder|filter feed]] on [[plankton]] and are usually less than {{Convert|10|cm|in|abbr=off}} long. They often stay together in [[Shoaling and schooling|schools]] and may [[Fish migration|migrate]] large distances between spawning grounds and feeding grounds. They are found particularly in [[upwelling]] regions around the northeast Atlantic, off the coast of Japan, and off the west coasts of Africa and the Americas. Forage fish are generally short-lived, and their [[Fish stocks|stocks]] fluctuate markedly over the years.<ref name="Checkley">Checkley D, Alheit J and Oozeki Y (2009) ''Climate Change and Small Pelagic Fish'', Cambridge University Press. {{ISBN|0-521-88482-9}}.</ref>
[[Herring]] are found in the [[North Sea]] and the [[North Atlantic]] at depths to {{Convert|200|m|ft|abbr=off}}. Important herring fisheries have existed in these areas for centuries. Herring of different sizes and growth rates belong to different populations, each of which have their own migration routes. When spawning, a female produces from 20,000 to 50,000 eggs. After spawning, the herrings are depleted of fat, and migrate back to feeding grounds rich in plankton.<ref name="pfa">[http://www.pfa-frozenfish.com/pfa2/fish1.html Pelagic species] {{webarchive|url=https://web.archive.org/web/20120211174604/http://www.pfa-frozenfish.com/pfa2/fish1.html |date=2012-02-11 }} Pelagic Freezer-trawler Association. Retrieved 22 July 2009.</ref> Around Iceland, three separate populations of herring were fished traditionally. These stocks collapsed in the late 1960s, although two have since recovered. After the collapse, Iceland turned to [[capelin]], which now account for about half of Iceland's total catch.<ref>[http://www.fisheries.is/main-species/pelagic-fishes/ Pelagic fishes] Icelandic fisheries. Retrieved 24 July 2009.</ref>
[[Blue whiting]] are found in the open ocean and above the [[continental slope]] at depths between 100 and 1000 meters . They follow vertical migrations of the [[zooplankton]] they feed on to the bottom during daytime and to the surface at night time.<ref name="pfa"/><ref>[http://www.imr.no/temasider/fisk/kolmule/kolmule/en Blue whiting] [[Institute of Marine Research]]. Retrieved 23 July 2009.</ref>
Traditional fisheries for [[Anchovy|anchovies]] and [[sardine]]s also have operated in the Pacific, the Mediterranean, and the southeast Atlantic.<ref name="Bone443">[[#Bone|Bone and Moore]], p. 443</ref> The world annual catch of forage fish in recent years has been approximately 22 million tonnes, or one quarter of the world's total catch.
<gallery class="left" widths="187" heights="167">
File:Pacific sardine002.jpg|These [[Shoaling and schooling|schooling]] [[Pacific sardine]]s are [[forage fish]].
File:Herringramkils.jpg|[[Herring]]s [[Forage fish#Hunting copepods|ram feeding]] on [[copepod]]s
File:Mallotus villosus.gif|[[Capelin]]
File:Anchovy closeup.jpg|[[Anchovy|Anchovies]]
File:Enrin u0.png|Peruvian anchoveta
</gallery>
===Predator fish===
{{See also|Predator fish}}
Medium size pelagic fishes include [[trevally]], [[barracuda]], [[flying fish]], [[bonito]], [[mahi mahi]], and coastal mackerel.<ref name="Lal8"/> Many of these fish hunt forage fish, but are in turn, hunted by yet larger pelagic fish. Nearly all fish are predator fish to some measure, and apart from the top predators, the distinction between predator fish and prey or forage fish, is somewhat artificial.<ref>[[FAO]]: LAPE project [http://www.fao.org/fishery/topic/4290/en Forage species] Rome. Updated 28 November 2008.</ref>
Around Europe there are three populations of coastal [[mackerel]]. One population migrates to the North Sea, another stays in the waters of the [[Irish Sea]], and the third population migrates southward along the west coast of Scotland and Ireland. The cruise speed of the mackerel is an impressive 10 kilometres per hour.<ref name="pfa"/><ref name="Mackerel">[http://www.imr.no/temasider/fisk/makrell/makrell/en Mackerel] [[Institute of Marine Research]]. Retrieved 23 July 2009.</ref>
Many large pelagic fish are oceanic nomadic species that undertake long offshore migrations. They feed on small pelagic forage fish, as well as medium-sized pelagic fish. At times, they follow their schooling prey, and many species form schools themselves.
Examples of larger pelagic fish are [[tuna]], [[billfish]], [[king mackerel]], sharks, and large [[Ray-finned fish|ray]]s.
Tuna in particular are of major importance to commercial fisheries. Although tuna migrate across oceans, trying to find them there is not the usual approach. Tuna tend to congregate in areas where food is abundant, along the boundaries of currents, around islands, near seamounts, and in some areas of upwelling along continental slopes. Tuna are captured by several methods: [[Seiner|purse seine vessels]] enclose an entire surface school with special nets, [[Fishing vessel#Line vessels|pole and line vessels]] that use poles baited with other smaller pelagic fish as [[baitfish]], and rafts called [[fish aggregating device]]s are set up, because tuna, as well as some other pelagic fish, tend to congregate under floating objects.<ref name="Lal8"/>
Other large pelagic fish are premier [[game fish]], particularly [[marlin]] and [[swordfish]].
<gallery class="left" widths="187" heights="167">
File:Yellowfin tuna nurp.jpg|[[Yellowfin tuna]] are being fished as a replacement for the now largely depleted [[Southern bluefin tuna]].
File:Brama brama.jpg|[[Atlantic pomfret]]
File:Xiphias gladius1.jpg|[[Swordfish]]
File:Sccav u0.gif|alt=King mackerels cruise on long migrations at 10 kilometres per hour|[[King mackerel]]s cruise on long migrations at 10 kilometres per hour.<ref name="pfa"/><ref name="Mackerel"/>
</gallery>
[[File:Ocean surface currents.jpg|thumb|right|450px|Major ocean surface currents]]
[[File:upwelling image1.jpg|thumb|right|300px|Areas of upwelling in red]]
[[File:La Nina and Pacific Decadal Anomalies - April 2008.png|thumb|right|300px|Pacific decadal anomalies – April 2008]]
===Productivity===
[[Upwelling]] occurs both along coastlines and in midocean when a collision of deep [[ocean current]]s brings cold water that is rich in nutrients to the surface. These upwellings support blooms of phytoplankton, which in turn, produce zooplankton and support many of the world's main fisheries. If the upwelling fails, then fisheries in the area fail.<ref name="Moyle574/5">[[#Moyle|Moyle and Cech]], pp. 574–575</ref>
In the 1960s the [[Peruvian anchoveta]] fishery was the world's largest fishery. The anchoveta population was greatly reduced during the 1972 [[El Niño]] event, when warm water drifted over the cold [[Humboldt Current]], as part of a 50-year cycle, lowering the depth of the [[thermocline]]. The upwelling stopped and [[phytoplankton]] production plummeted, as did the anchoveta population, and millions of [[seabird]]s, dependent on the anchoveta, died.<ref>{{Cite journal | doi = 10.1126/science.1075880| pmid = 12522241| title = From Anchovies to Sardines and Back: Multidecadal Change in the Pacific Ocean| journal = Science| volume = 299| issue = 5604| pages = 217–21| year = 2003| last1 = Chavez | first1 = F. P.| last2 = Ryan| first2 = John| last3 = Lluch-Cota| first3 = Salvador E.| last4 = Ñiquen c.| first4 = Miguel| bibcode = 2003Sci...299..217C| s2cid = 37990897}}</ref> Since the mid-1980s, the upwelling has resumed, and the Peruvian anchoveta catch levels have returned to the 1960s levels.
Off Japan, the collision of the [[Oyashio Current]] with the [[Kuroshio Current]] produces nutrient-rich upwellings. Cyclic changes in these currents resulted in a decline in the [[sardine]] ''sardinops melanosticta'' populations. Fisheries catches fell from 5 million tonnes in 1988 to 280 thousand tonnes in 1998. As a further consequence, [[Pacific bluefin tuna]] stopped moving into the region to feed.<ref>{{Cite journal | doi = 10.1111/j.1365-2419.1996.tb00110.x| title = Decadal variation in the trans-Pacific migration of northern bluefin tuna (''Thunnus thynnus'') coherent with climate-induced change in prey abundance| journal = Fisheries Oceanography| volume = 5| issue = 2| pages = 114–119| year = 1996| last1 = Polovina | first1 = J. J. | url = https://zenodo.org/record/1230607}}</ref><ref>[[FAO]]: Species Fact Sheets: [http://www.fao.org/fishery/species/2893/en ''Sardinops melanostictus'' (Schlegel, 1846)] Rome. Retrieved 18 August 2009.</ref>
Ocean currents can shape how fish are distributed, both concentrating and dispersing them. Adjacent ocean currents can define distinct, if shifting, boundaries. These boundaries can even be visible, but usually their presence is marked by rapid changes in salinity, temperature, and turbidity.<ref name="Moyle574/5" />
For example, in the Asian northern Pacific, [[albacore]] are confined between two current systems. The northern boundary is determined by the cold [[North Pacific Current]] and the southern boundary is determined by the [[North Equatorial Current]]. To complicate things, their distribution is further modified within the area defined by the two current systems by another current, the [[Kuroshio Current]], whose flows fluctuate seasonally.<ref>{{cite book|author=Nakamura, Hiroshi |title=Tuna distribution and migration|url=https://books.google.com/books?id=SygRAAAAYAAJ|year=1969|publisher=Fishing News|isbn=9780852380024}}</ref>
Epipelagic fish often [[spawn (biology)|spawn]] in an area where the eggs and larvae drift downstream into suitable feeding areas, and eventually, drift into adult feeding areas.<ref name="Moyle574/5" />
Islands and [[Fishing bank|banks]] can interact with currents and upwellings in a manner that results in areas of high ocean productivity. Large eddies can form downcurrent or downwind from islands, concentrating plankton.<ref>{{cite journal|author=Blackburn M |year=1965|title=Oceanography and the ecology of tunas|journal=Oceanography and Marine Biology: An Annual Review|volume=3|pages=299–322|url=http://fsf.fra.affrc.go.jp/bulletin/kenpoupdf/kenpou2-257.pdf}}</ref> Banks and reefs can intercept deep currents that upwell.<ref name="Moyle574/5" />
* [[Scombrid]]s
===Highly migratory species===
{{See also|Highly migratory species}}
[[File:Isurus-oxyrinchus.jpg|thumb|left|[[Shortfin mako shark]] make long seasonal migrations. They appear to follow temperature gradients, and have been recorded travelling more than 4,500 km in one year.<ref>{{Cite journal | doi = 10.1071/MF9920045| title = Tagging studies on the Shortfin Mako Shark (''Isurus oxyrinchus'') in the Western North Atlantic| journal = Marine and Freshwater Research| volume = 43| pages = 45| year = 1992| last1 = Casey | first1 = J. G. | last2 = Kohler | first2 = N. E. }}</ref>]]
Epipelagic fish generally move long distances between feeding and spawning areas, or as a response to changes in the ocean. Large ocean predators, such as salmon and tuna, can migrate thousands of kilometres, crossing oceans.<ref name="Moyle578">[[#Moyle|Moyle and Cech]], p. 578</ref>
In a 2001 study, the movements of [[Atlantic bluefin tuna]] from an area off North Carolina were studied with the help of special popup tags. When attached to a tuna, these tags monitored the movements of the tuna for about a year, then detached and floated to the surface where they transmitted their information to a satellite. The study found that the tuna had four different migration patterns. One group confined itself to the western Atlantic for a year. Another group also stayed mainly in the western Atlantic, but migrated to the Gulf of Mexico for spawning. A third group moved across the Atlantic Ocean and back again. The fourth group crossed to the eastern Atlantic and then moved into the Mediterranean Sea for spawning. The study indicates that, while there is some differentiation by spawning areas, there is essentially only one population of Atlantic bluefin tuna, intermixing groups that between them, use all of the north Atlantic Ocean, the Gulf of Mexico, and the Mediterranean Sea.<ref>{{Cite journal | doi = 10.1126/science.1061197|pmid=11509729|url=http://www.tunaresearch.org/reprints/migratory2001.pdf| title = Migratory Movements, Depth Preferences, and Thermal Biology of Atlantic Bluefin Tuna| journal = Science| volume = 293| issue = 5533| pages = 1310–4| year = 2001| last1 = Block | first1 = B. A.|last2=Dewar|first2=H|last3=Blackwell|first3=S. B.|last4=Williams|first4=T. D.|last5=Prince|first5=E. D.|last6=Farwell|first6=C. J.|last7=Boustany|first7=A|last8=Teo|first8=S. L.|last9=Seitz|first9=A|last10=Walli|first10=A|last11=Fudge|first11=D|bibcode=2001Sci...293.1310B|s2cid=32126319}}</ref>
The term [[highly migratory species]] (HMS) is a legal term that has its origins in Article 64 of the [[United Nations Convention on the Law of the Sea]] (UNCLOS).<ref>[[United Nations]] Convention on the [[Law of the Sea]]: [https://www.un.org/Depts/los/convention_agreements/texts/unclos/closindx.htm Text]</ref>
The highly migratory species include: [[tuna]] and tuna-like species ([[Albacore tuna|albacore]], Atlantic bluefin, [[bigeye tuna]], [[Skipjack tuna|skipjack]], [[Yellowfin tuna|yellowfin]], [[Blackfin tuna|blackfin]], [[Euthynnus alletteratus|little tunny]], [[Pacific bluefin tuna|Pacific bluefin]], [[Southern bluefin tuna|southern bluefin]] and [[Auxis rochei|bullet]]), [[Bramidae|pomfret]], [[marlin]], [[sailfish]], [[swordfish]], [[saury]] and oceangoing [[shark]]s, as well as mammals such as [[dolphin]]s, and other [[cetacean]]s.
Essentially, highly migratory species coincide with the larger of the "large pelagic fish", discussed in the previous section, if cetaceans are added and some commercially unimportant fish, such as the [[Molidae|sunfish]], are excluded. These are high [[trophic level]] species that undertake migrations of significant, but variable distances across oceans for feeding, often on forage fish, or reproduction, and also have wide geographic distributions. Thus, these species are found both inside the {{convert|200|nmi|km|adj=on}} [[exclusive economic zone]]s and in the [[high seas]] outside these zones. They are [[pelagic]] species, which means they mostly live in the open ocean and do not live near the sea floor, although they may spend part of their life cycle in [[nearshore waters]].<ref>[[Pacific Fishery Management Council]]: [http://www.pcouncil.org/hms/hmsback.html Background: Highly Migratory Species] {{Webarchive|url=https://web.archive.org/web/20090712150423/http://www.pcouncil.org/hms/hmsback.html |date=2009-07-12 }}</ref>
===Capture production===
According to the [[Food and Agriculture Organization]] (FAO), the [[Fishing by country|world harvest]] in 2005 consisted of 93.2 million [[tonne]]s captured by [[commercial fishing]] in [[wild fisheries]].<ref>[http://www.fao.org/fishery/ Fisheries and Aquaculture]. FAO. Retrieved on 2015-05-01.</ref> Of this total, about 45% were pelagic fish. The following table shows the world capture production in [[tonne]]s.<ref>[[FAO]] (2007) [http://www.fao.org/docrep/009/A0699e/A0699e00.htm ''State of the World Fisheries and Aquaculture 2006.''] Fisheries and Aquaculture Department. {{ISBN|978-92-5-105568-7}}</ref>
{| class="sortable wikitable"
|-
! colspan="9" style="text-align:center; width:640px;"| '''Capture production by groups of species in tonnes'''
|-
! style="width:45px;"| Type
! style="width:100px;"| Group
! 1999
! 2000
! 2001
! 2002
! 2003
! 2004
! 2005
|-
| Small pelagic fish
| [[Herring]]s, [[sardine]]s, [[Anchovy|anchovies]]
| 22 671 427
| 24 919 239
| 20 640 734
| 22 289 332
| 18 840 389
| 23 047 541
| 22 404 769
|-
| Large pelagic fish
| [[Tuna]]s, [[bonito]]s, [[billfish]]es
| 5 943 593
| 5 816 647
| 5 782 841
| 6 138 999
| 6 197 087
| 6 160 868
| 6 243 122
|-
| Other pelagic fish
|
| 10 712 994
| 10 654 041
| 12 332 170
| 11 772 320
| 11 525 390
| 11 181 871
| 11 179 641
|-
| [[Cartilaginous fish]]
| [[Shark]]s, [[Batoidea|rays]], [[chimaera]]s
| 858 007
| 870 455
| 845 854
| 845 820
| 880 785
| 819 012
| 771 105
|}
==Threatened species==
In 2009, the [[International Union for Conservation of Nature]] (IUCN) produced the first [[IUCN Red List|red list]] for threatened oceanic sharks and rays. They claim that approximately one third of open ocean sharks and rays are under [[Threatened species|threat of extinction]].<ref>[http://www.iucn.org/?3362/Third-of-open-ocean-sharks-threatened-with-extinction Third of open ocean sharks threatened with extinction] [[IUCN]]. 25 June 2009.</ref> There are 64 species of oceanic sharks and rays on the list, including [[Hammerhead shark|hammerhead]]s, giant [[Mobula|devil ray]]s, and [[porbeagle]].<ref name="guardian">[https://www.theguardian.com/science/2009/jun/25/sharks-extinction-iucn-red-list Fishing puts a third of all oceanic shark species at risk of extinction] ''[[guardian.co.uk]]'', 26 June 2009.</ref>
Oceanic sharks are [[incidental catch|captured incidentally]] by swordfish and tuna [[high seas]] fisheries. In the past there were few markets for sharks, which were regarded as worthless [[bycatch]]. Now sharks are being increasingly targeted to supply emerging Asian markets, particularly for [[Shark finning|shark fins]], which are used in [[shark fin soup]].<ref name="guardian"/>
The northwest Atlantic Ocean shark populations are estimated to have declined by 50% since the early 1970s. Oceanic sharks are vulnerable because they do not produce many young, and the young can take decades to mature.<ref name="guardian"/>
<gallery class="left" widths="200" heights="175">
File:Sphyrnalewini.jpg|The [[scalloped hammerhead]] is classified as endangered.
File:Oceanic Whitetip Shark.png|alt=The oceanic whitetip shark has declined by 99% in the Gulf of Mexico|The [[oceanic whitetip shark]] has declined by 99% in the [[Gulf of Mexico]].<ref name="guardian"/>
File:Atlantic mobula lisbon.jpg|The [[devil fish]], a large ray, is threatened.
File:Lamna nasus.jpg|The [[Porbeagle|porbeagle shark]] is threatened.
</gallery>
In parts of the world the [[scalloped hammerhead]] shark has declined by 99% since the late 1970s. Its status on the red list is that it is globally endangered, meaning it is near extinction.<ref name="guardian"/>
==See also==
{{div col|colwidth=22em}}
* [[Deep sea]]
* [[Deep sea fish]]
* [[Demersal fish]]
* [[Freshwater fish]]
* [[Nekton]]
* [[Ocean Tracking Network]]
* [[Oily fish]]
* [[Pacific Ocean Shelf Tracking Project]]
* [[Tagging of Pacific Predators]]
{{div col end}}
==References==
'''Notes'''
{{Reflist|30em}}
'''Bibliography'''
* {{cite book|ref=Bone|author1=Bone, Quentin |author2=Moore, Richard |title=Biology of Fishes|url=https://books.google.com/books?id=sLoqT_xWaqoC|date=2008|publisher=Garland Science|isbn=978-0-203-88522-2}}
*{{cite book|ref=Moyle|author1=Moyle, PB |author2=Cech, JJ |name-list-style=amp |year=2004|title=Fishes, An Introduction to Ichthyology|edition=5th|publisher=Benjamin Cummings|isbn=978-0-13-100847-2}}
==Further reading==
* Collette, BB (2010) [https://books.google.com/books?hl=en&lr=&id=_4xZ_QoYNSwC&oi=fnd&pg=PA21 "Reproduction and development in epipelagic fishes"] In: Kathleen S Cole, ''Reproduction and Sexuality in Marine Fishes: Patterns and Processes'', pp. 21–64, University of California Press. {{ISBN|978-0-520-26433-5}}.
* Freon, Pierre (1998) ''Dynamics of Pelagic Fish Distribution and Behaviour: Effects on Fisheries and Stock Assessment'', Wiley-Blackwell. {{ISBN|978-0-85238-241-7}}.
* {{cite journal | last1 = Johnsen | first1 = S | year = 2003 | title = Lifting the Cloak of Invisibility: The Effects of Changing Optical Conditions on Pelagic Crypsis1 | journal = Integrative and Comparative Biology | volume = 43 | issue = 4| pages = 580–590 | doi=10.1093/icb/43.4.580 | pmid=21680466| doi-access = free }}
* {{cite journal | last1 = Makris | first1 = N | last2 = Ratilal | first2 = P | last3 = Jagannathan | first3 = S | last4 = Gong | first4 = Z | last5 = Andrews | first5 = M | last6 = Bertsatos | first6 = I | last7 = Godo | first7 = OR | last8 = Nero | first8 = RW | last9 = Jech | first9 = JM | year = 2009 | title = Critical Population Density Triggers Rapid Formation of Vast Oceanic Fish Shoals | url = http://www.sciencemag.org/cgi/content/abstract/323/5922/1734 | journal = Science | volume = 323 | issue = 5922| pages = 1734–1737 | doi=10.1126/science.1169441 | pmid=19325116| bibcode = 2009Sci...323.1734M | s2cid = 6478019 }}
* Pepperell J (2011) [https://books.google.com/books?id=ZaSuYgEACAAJ ''Fishes of the Open Ocean: A Natural History and Illustrated Guide''] University of New South Wales Press, {{ISBN|978-1-74223-267-6}}.
* Salvanesa AGV and Kristoffersen JB [https://web.archive.org/web/20090521003502/http://www.bio.uib.no/inc/pdffiles/Pub/1325.pdf "Mesopelagic Fishes"] In: ''Encyclopedia of Ocean Sciences'', pp. 1711–1717. {{doi|10.1006/rwos.2001.0012}}
* [https://phys.org/news/2009-03-scientists-ids-genesis-animal-behavior.html Scientists IDs genesis of animal behavior patterns] ''[[PhysOrg.com]]'', 26 March 2009.
* [https://phys.org/news/2006-02-fish-mit-sensor.html One fish, two fish: New MIT sensor improves fish counts] ''[[PhysOrg.com]]'', 2 February 2006.
==External links==
{{Commons category|Deep sea fish}}
* [https://www.ted.com/talks/edith_widder_glowing_life_in_an_underwater_world Glowing life in an underwater world] TED video from [[Edith Widder]]
* [https://web.archive.org/web/20140625125029/http://marinebio.org/oceans/open-ocean.asp The Open Ocean] ''MarineBio.org''. MarineBio.org. Updated 28 August 2011. TED video from [[Edith Widder]]
* [https://web.archive.org/web/20140625125029/http://marinebio.org/oceans/open-ocean.asp The Open Ocean] ''MarineBio.org''. MarineBio.org. Updated 28 August 2011.
* [https://www.pelagic-ac.org/ Pelagic Advisory Council] of the [[European Commission]]
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