Saltwater fish, also called marine fish or sea fish, are fish that live in

seawater Seawater, or salt water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has appro ...

. Saltwater fish can swim and live alone or in a large group called a

school A school is an educational institution designed to provide learning spaces and learning environments for the teaching of students under the direction of teachers. Most countries have systems of formal education, which is sometimes co ...

. Saltwater fish are very commonly kept in aquariums for

entertainment Entertainment is a form of activity that holds the attention and interest of an audience or gives pleasure and delight. It can be an idea or a task, but is more likely to be one of the activities or events that have developed over thousa ...

. Many saltwater fish are also caught to be eaten, or grown in

aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. lot ...

. However, many fish species have been

overfished Overfishing is the removal of a species of fish (i.e. fishing) from a body of water at a rate greater than that the species can replenish its population naturally (i.e. the overexploitation of the fishery's existing fish stock), resulting in ...

and are otherwise threatened by

marine pollution Marine pollution occurs when substances used or spread by humans, such as industrial, agricultural and residential waste, particles, noise, excess carbon dioxide or invasive organisms enter the ocean and cause harmful effects there. The major ...

or ecological changes caused by

climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...

Diet

Fishes that live in the ocean can be

carnivore A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other s ...

herbivore A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...

s, or

omnivore An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nu ...

s. Herbivores in the ocean eat things such as

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular micr ...

and flowering

seagrass Seagrasses are the only flowering plants which grow in marine environments. There are about 60 species of fully marine seagrasses which belong to four families ( Posidoniaceae, Zosteraceae, Hydrocharitaceae and Cymodoceaceae), all in the ...

es. Many herbivores' diets consist of primarily algae. Most saltwater fish will eat both

macroalgae Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of '' Rhodophyta'' (red), ''Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as ...

and

microalgae Microalgae or microphytes are microscopic algae invisible to the naked eye. They are phytoplankton typically found in freshwater and marine systems, living in both the water column and sediment. They are unicellular species which exist indiv ...

. Many fish eat red, green, brown, and blue algae, but some fish prefer certain types. Most saltwater fish that are carnivores will never eat algae under any circumstances. Carnivores' diets consist of

shrimp Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are ref ...

plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a cruc ...

, or tiny

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapoda, decapods, ostracoda, seed shrimp, branchiopoda, branchiopods, argulidae, fish lice, krill, remipedes, isopoda, isopods, barnacles, copepods, ...

Captivity

Saltwater

aquarium An aquarium (plural: ''aquariums'' or ''aquaria'') is a vivarium of any size having at least one transparent side in which aquatic plants or animals are kept and displayed. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, aq ...

s are a multi-million dollar industry in the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

. About 10 million marine fish are imported into the United States each year for aquarium use. The United States imports more

saltwater Saline water (more commonly known as salt water) is water that contains a high concentration of dissolved salts (mainly sodium chloride). On the United States Geological Survey (USGS) salinity scale, saline water is saltier than brackish water, ...

fish than any other country in the world. There are approximately 2,000 different

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...

of saltwater fish that are imported and used in

captivity Captivity, or being held captive, is a state wherein humans or other animals are confined to a particular space and prevented from leaving or moving freely. An example in humans is imprisonment. Prisoners of war are usually held in captivity by a ...

. In many circumstances, fish used for marine trade are collected using harmful tactics such as

cyanide Cyanide is a naturally occurring, rapidly acting, toxic chemical that can exist in many different forms. In chemistry, a cyanide () is a chemical compound that contains a functional group. This group, known as the cyano group, consists of ...

. One way that people are trying to protect the

coral reef A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of Colony (biology), colonies of coral polyp (zoology), polyps held together by calcium carbonate. Most coral reefs are built from stony corals, wh ...

s is by

breeding Breeding is sexual reproduction that produces offspring, usually animals or plants. It can only occur between a male and a female animal or plant. Breeding may refer to: * Animal husbandry, through selected specimens such as dogs, horses, and r ...

marine fish in

. Captive-bred fish are known to be healthier and likely to live longer. Captive-bred fish are less susceptible to disease because they have not been exposed to the wild and they have not been damaged during the shipment process. Fish that are bred in captivity are already accustomed to aquarium

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

s and food.

Habitats

There are many different components that make up a marine life

. Some of them are the

temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...

of the water, the quality, and quantity of water (flow and depth). Other components that can also contribute to the habitat of saltwater fish are pH level, salt level, and alkalinity level. Levels of nitrates and phosphates are also relevant, particularly when considering conditions for fish in captivity. There are other physical features that contribute to a habitat which are physical materials like rocks, reefs, and sand or the

vegetation Vegetation is an assemblage of plant species and the ground cover they provide. It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic charac ...

like the amount of algae, water plants, and

saltmarsh A salt marsh or saltmarsh, also known as a coastal salt marsh or a tidal marsh, is a coastal ecosystem in the upper coastal intertidal zone between land and open saltwater or brackish water that is regularly flooded by the tides. It is dominated ...

. Specific fish live in specific habitats based on what they eat or what cycle of life they are currently at, another thing is the amount of salt that is in the water at that specific location. Another thing is that some ocean habitats aren't technically in the ocean and these are called

estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environme ...

, areas when oceans and rivers meet creating a mixture of salt water and freshwater making a different habitat for different types of fish and creatures to live in. The ocean is home to

organism In biology, an organism () is any living system that functions as an individual entity. All organisms are composed of cells ( cell theory). Organisms are classified by taxonomy into groups such as multicellular animals, plants, and fu ...

s as large as

whale Whales are a widely distributed and diverse group of fully aquatic placental marine mammals. As an informal and colloquial grouping, they correspond to large members of the infraorder Cetacea, i.e. all cetaceans apart from dolphins and ...

s and as small as microscopic marine organisms such as

phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'. ...

. However, the vast majority of ocean life that humans are exposed to is simple saltwater fish. Saltwater fish can live in the deepest depths of the ocean where no sunlight can penetrate, but they can also live on the surface of the water.

Threats

Marine fish face many anthropogenic threats. Common human-induced threats include overfishing, pollution, habitat loss and destruction, climate change and invasive species. The aforementioned threats all come with a multitude of negative direct and indirect affects to marine ecosystems. With the human population growing at an exponential rate, these threats are likely to continue to be prevalent in marine ecosystems. Trawlers overfishing cod

Overfishing

Overfishing Overfishing is the removal of a species of fish (i.e. fishing) from a body of water at a rate greater than that the species can replenish its population naturally (i.e. the overexploitation of the fishery's existing fish stock), resulting in t ...

is defined as the mass removal of fish from a body of water that results in halting the ability for breeding populations to replenish what has been removed. Fish is one of the most popular foods in the world and consumption has continued to rise with the growing human population and will continue to do so. The value of the global seafood market has seen a 15% increase from 2016 to 2020 and is projected to increase even more by 2023. Although it provides many people with a source of food, the global seafood market is a major threat to the biodiversity of fishes.

Bycatch Bycatch (or by-catch), in the fishing industry, is a fish or other marine species that is caught unintentionally while fishing for specific species or sizes of wildlife. Bycatch is either the wrong species, the wrong sex, or is undersized or juve ...

is a direct effect of overfishing and is defined as the unwanted capture of different marine organisms during industrial fishing. This results in many different species of fish dying after they are captured and discarded. Data on bycatch is often unclear and not well recorded but it is estimated that the U.S. alone discards 17-22% of their catch annually. The

Mesopredator release hypothesis The mesopredator release hypothesis is an ecological theory used to describe the interrelated population dynamics between apex predators and mesopredators within an ecosystem, such that a collapsing population of the former results in dramatically ...

is one of the indirect effects of overfishing that is also often referred to as "

fishing down the food web Fishing down the food web is the process whereby fisheries in a given ecosystem, "having depleted the large predatory fish on top of the food web, turn to increasingly smaller species, finally ending up with previously spurned Forage fish, small f ...

". This phenomenon means as fisheries deplete large apex predatory species, mid-sized predatory species increase in abundance and assume the role as top predators on the food web. This impacts the food web in marine environments and disrupts the balance of the ecosystem and is likely to cause trophic cascades.

Species affected by overfishing

Profitable fish stocks like the

bluefin tuna Bluefin tuna is a common name used to refer to several species of tuna A tuna is a saltwater fish that belongs to the tribe Thunnini, a subgrouping of the Scombridae (mackerel) family. The Thunnini comprise 15 species across five genera, th ...

are decreasing in numbers because of high demand. According to the IUCN Red List, the

Pacific bluefin tuna The Pacific bluefin tuna (''Thunnus orientalis'') is a predatory species of tuna found widely in the northern Pacific Ocean, but it is migratory and also recorded as a visitor to the south Pacific. In the past it was often included in '' T. t ...

Atlantic bluefin tuna The Atlantic bluefin tuna (''Thunnus thynnus'') is a species of tuna in the family Scombridae. It is variously known as the northern bluefin tuna (mainly when including Pacific bluefin as a subspecies), giant bluefin tuna or individuals exce ...

, and

southern bluefin tuna The southern bluefin tuna (''Thunnus maccoyii'') is a tuna of the family Scombridae found in open southern Hemisphere waters of all the world's oceans mainly between 30°S and 50°S, to nearly 60°S. At up to and weighing up to , it is among ...

are classified as vulnerable, endangered and critically endangered all due to over-exploitation. According to the IUCN Red List, the

oceanic whitetip shark The oceanic whitetip shark (''Carcharhinus longimanus''), also known as shipwreck shark, Brown Milbert's sand bar shark, brown shark, lesser white shark, nigano shark, oceanic white-tipped whaler, and silvertip shark, is a large pelagic requiem ...

is considered critically endangered because of its value in the seafood market. Their rapidly declining population is due to people overfishing them for their fins. They are a popular species of shark used in

shark fin soup Shark fin soup is a traditional soup or stewed dish served in parts of China, Taiwan, and Southeast Asia. The shark fins provide texture, while the taste comes from the other soup ingredients. It is commonly served at special occasions such as ...

because of the size of their fins. All sharks are used for shark fin soup, however, certain species of sharks are preferred over others because of the large size of their fins. The

great white shark The great white shark (''Carcharodon carcharias''), also known as the white shark, white pointer, or simply great white, is a species of large mackerel shark which can be found in the coastal surface waters of all the major oceans. It is nota ...

is listed as vulnerable on the IUCN Red List because its fins are commonly used in shark fin soup and has led to people over harvesting them for their fins. This shark belongs to the class

Chondrichthyes Chondrichthyes (; ) is a class that contains the cartilaginous fishes that have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fishes'', which have skeletons primarily composed of bone tissue. ...

that includes all sharks, skates and rays. The great white shark is one of the many examples of shark species threatened by human consumption because of the shark fin soup, large population declines of this class has been noted since the early 2000s due to the high demand for their fins, gill rakers and liver oil. The

Atlantic cod The Atlantic cod (''Gadus morhua'') is a benthopelagic fish of the family Gadidae, widely consumed by humans. It is also commercially known as cod or codling.New England New England is a region comprising six states in the Northeastern United States: Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont. It is bordered by the state of New York to the west and by the Canadian provinces ...

. Due to its low fat content and dense white flesh, this fish is a popular choice among humans. Now considered vulnerable, its populations have both decreased in abundance and their distribution has shifted from northern to southern areas due to overfishing.

Cage aquaculture

Aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. lot ...

is defined as the farming of aquatic organisms in controlled environments for the purpose of providing food and resources for humans. Aquaculture can take place in both marine and freshwater environments, however, because this is the saltwater fish page this entry will only cover the effects of aquaculture on marine fishes. The rising global demand for fish has contributed to the increase in aquaculture. Due to the decline of many wild fish stocks, aquaculture is the fastest growing food production system that contributes about 50% of the worlds fish supply. There is a lot of debate on whether or not aquaculture is an environmentally sustainable practice, yet the socioeconomic benefits that humans receive is tough to argue against. That being said there are significant negative effects that aquaculture, especially cage aquaculture, has on the surrounding environment. Cage aquaculture involves rearing aquatic organisms in natural water sources while enclosed in a mesh/net cage that allows water from the surrounding environment to freely flow in and out. Cage aquaculture in marine environments has been particularly controversial because of the effects it has on the surrounding ecosystem thus, affecting wild marine fish populations. The main impacts of cage aquaculture are reduced water quality from fish sewage, high potential of

genetic pollution Genetic pollution is a controversial term for uncontrolled gene flow into wild populations. It is defined as "the dispersal of contaminated altered genes from genetically engineered organisms to natural organisms, esp. by cross-pollination", but ...

of wild stocks due to escapees from aquaculture cages and the possibility of introducing an invasive species if the fish being reared are non-native . Fish sewage is the combination of fish feed, fecal material and antibiotics that is accumulated on the seafloor and in the water column from fish that are being farmed. It is not only harmful to wild fish stocks but it also poses a threat to marine plant life which is often a food source for wild fish stocks. Fish sewage is harmful because it pollutes the surrounding ecosystem and can cause problems like eutrophication, transmission of parasites and diseases to wild populations and developmental abnormalities on surrounding wild fish. Genetic pollution of wild fish populations is a common risk that cage aquaculture faces. For example, there are many scientific papers that have examined the effects of Atlantic Salmon escaping from their enclosures and interacting with wild populations. Farmed salmon have lower fitness (low survival rates and reproductive success) than a wild salmon would due to differences in artificial and natural selection. Artificial selection that chooses phenotypic traits that are desired for human consumption will alter the genetics of wild stocks if farmed fish interact and breed with wild populations. This would result in the reduction of fitness related traits that wild stocks possess which is a serious threat to these populations.

Categorization of saltwater fish by habitats

* Coastal fish (also offshore fish or neritic fish) inhabit the sea between the shoreline and the edge of the

continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...

Deep sea fish Deep-sea fish are fish that live in the darkness below the sunlit surface waters, that is below the epipelagic or photic zone of the sea. The lanternfish is, by far, the most common deep-sea fish. Other deep sea fishes include the flashligh ...

live below the

photic zone The photic zone, euphotic zone, epipelagic zone, or sunlight zone is the uppermost layer of a body of water that receives sunlight, allowing phytoplankton to perform photosynthesis. It undergoes a series of physical, chemical, and biological pro ...

of the ocean, i.e. where not enough light penetrates for

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...

to occur *

Pelagic fish Pelagic fish live in the pelagic zone of ocean or lake waters—being neither close to the bottom nor near the shore—in contrast with demersal fish that do live on or near the bottom, and reef fish that are associated with coral re ...

live near the surface of the sea or a lake *

Demersal fish Demersal fish, also known as groundfish, live and feed on or near the bottom of seas or lakes (the demersal zone).Walrond Carl . "Coastal fish - Fish of the open sea floor"Te Ara - the Encyclopedia of New Zealand. Updated 2 March 2009 They oc ...

live on or near the bottom of the sea or a lake *

Coral reef fish Coral reef fish are fish which live amongst or in close relation to coral reefs. Coral reefs form complex ecosystems with tremendous biodiversity. Among the myriad inhabitants, the fish stand out as colourful and interesting to watch. Hundreds ...

are associated with a

References

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