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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Deep-sea fish | 6/6 | https://en.wikipedia.org/wiki/Deep-sea_fish | reference | science, encyclopedia | 2026-05-05T07:34:47.616452+00:00 | kb-cron |
== Adaptation to high pressure == As a fish moves deeper into the sea, the weight of the water overhead exerts increasing hydrostatic pressure on the fish. This increased pressure amounts to about one atm (0.1 MPa) for every 10 m (33 ft)in depth. For a fish at the bottom of the bathypelagic zone, this pressure amounts to about 400 atm (40 MPa, 6000 psi). Deep-sea organisms possess adaptations at cellular and physiological levels that allow them to survive in environments of great pressure. Not having these adaptations limits the depths at which shallow-water species can operate. High levels of external pressure affects how metabolic processes and biochemical reactions proceed. The equilibrium of many chemical reactions is disturbed by pressure, and pressure can inhibit processes which result in an increase in volume. Water, a key component in many biological processes, is very susceptible to volume changes, mainly because constituents of cellular fluid have an effect on water structure. Thus, enzymatic reactions that induce changes in water organization effectively change the system's volume. Proteins responsible for catalyzing reactions are typically held together by weak bonds and the reactions usually involve volume increases. Species that can tolerate these depths have evolved changes in their protein structure and reaction criteria to withstand pressure, in order to perform reactions in these conditions. In high pressure environments, bilayer cellular membranes experience a loss of fluidity. Deep-sea cellular membranes favor phospholipid bilayers with a higher proportion of unsaturated fatty acids, which induce a higher fluidity than their sea-level counterparts. Ten orders, thirteen families and about 200 known species of deep-sea fish have evolved a gelatinous layer below the skin or around the spine, which is used for buoyancy, low-cost growth and to increase swimming efficiency by reducing drag.
Deep-sea species exhibit lower changes of entropy and enthalpy compared to surface level organisms, since a high pressure and low temperature environment favors negative enthalpy changes and reduced dependence on entropy-driven reactions. From a structural standpoint, globular proteins of deep-sea fish due to the tertiary structure of G-actin are relatively rigid compared to those of surface level fish. The fact that proteins in deep-sea fish are structurally different from surface fish is apparent from the observation that actin from the muscle fibers of deep-sea fish are extremely heat-resistant; an observation similar to what is found in lizards. These proteins are structurally strengthened by modification of the bonds in the tertiary structure of the protein which also happens to induce high levels of thermal stability. Proteins are structurally strengthened to resist pressure by modification of bonds in the tertiary structure. Therefore, high levels of hydrostatic pressure, similar to high body temperatures of thermophilic desert reptiles, favor rigid protein structures.
Na+/K+ -ATPase is a lipoprotein enzyme that plays a prominent role in osmoregulation and is heavily influenced by hydrostatic pressure. The inhibition of Na+/K+ -ATPase is due to increased compression due to pressure. The rate-limiting step of the Na+/K+ -ATPase reaction induces an expansion in the bilayer surrounding the protein, and therefore an increase in volume. An increase in volume makes Na+/K+ -ATPase reactivity susceptible to higher pressures. Even though the Na+/K+ -ATPase activity per gram of gill tissue is lower for deep-sea fishes, the Na+/K+ -ATPases of deep-sea fishes exhibit a much higher tolerance of hydrostatic pressure compared to their shallow-water counterparts. This is exemplified between the species C. acrolepis (around 2000 m deep) and its hadalpelagic counterpart C. armatus (around 4,000 metres (13,123 ft) deep), where the Na+/K+ -ATPases of C. armatus are much less sensitive to pressure. This resistance to pressure can be explained by adaptations in the protein and lipid moieties of Na+/K+ -ATPase.
== Lanternfish ==
Sampling via deep trawling indicates that lanternfish account for as much as 65% of all deep-sea fish biomass. Indeed, lanternfish are among the most widely distributed, populous, and diverse of all vertebrates, playing an important ecological role as prey for larger organisms. With an estimated global biomass of 550–660 million metric tons, 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. In the Southern Ocean, Myctophids provide an alternative food resource to krill for predators such as squid and the king penguin. Although these fish are plentiful and prolific, currently only a few commercial lanternfish fisheries exist: these include limited operations off South Africa, in the sub-Antarctic, and in the Gulf of Oman.
== Endangered species == A 2006 study by Canadian scientists has found five species of deep-sea fish – blue hake, spiny eel – to be on the verge of extinction due to the shift of commercial fishing from continental shelves to the slopes of the continental shelves, down to depths of 1,600 metres (5,249 ft). The slow reproduction of these fish – they reach sexual maturity at about the same age as human beings – is one of the main reasons that they cannot recover from the excessive fishing.
== See also ==
Census of Marine Life Deep ocean water Deep sea Deep-sea community Demersal fish Pelagic fish
== Citations ==
== References ==
== Further reading == Gordon J. D. M. (2001) "Deep-sea fishes" In: John H. Steele, Steve A. Thorpe, Karl K. Turekian (eds.) Elements of Physical Oceanography, pages 227–233, Academic Press. ISBN 9780123757241. Hoar W. S., Randall D. J. and Farrell A. P. (eds.) (1997) Deep-Sea Fishes, Academic Press. ISBN 9780080585406. Shotton, Ross (1995) "Deepwater fisheries" In: Review of the state of world marine fishery resources, FAO Fisheries technical paper 457, FAO, Rome. ISBN 92-5-105267-0. Tandstad M., Shotton R., Sanders J. and Carocci F. (2011) "Deep-sea Fisheries" Archived 3 March 2016 at the Wayback Machine In: Review of the state of world marine fishery resources, pages 265–278, FAO Fisheries technical paper 569, FAO, Rome. ISBN 978-92-5-107023-9.
== External links ==
Deep-Sea Bestiary Photo Gallery: Deep-Sea Creatures Crash Course To Deep Sea Fishing – articles, facts and images of deep-sea animals