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About 18,000 described species of marine fish are currently recognized. FishBase counted 18,080 marine fish species in February 2026, although the total changes as scientists discover new fish and revise classifications.
About 18,000 described species of marine fish are currently recognized. FishBase counted 18,080 marine fish species in its February 2026 statistics. That is the best concise answer, but it is not a permanent total: scientists continue to discover fish, and taxonomists regularly split, merge, or reclassify species.
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The number also depends on what counts as “in the ocean.” Some fish live in seawater, some use estuaries or brackish water, and others migrate between fresh and salt water. So a precise answer needs a definition as well as a number.
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Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallWhat does “type of fish” mean?
In everyday conversation, “type” might mean a familiar group such as sharks, rays, eels, tuna, or reef fish. Biologists usually answer this question using species—the most useful unit for counting distinct kinds of animals.
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“Fish” is also an informal biological grouping rather than one single, neatly bounded taxonomic class. Living fish include several major lineages, including:
- Hagfishes
- Lampreys
- Sharks and rays
- Chimaeras, sometimes called ghost sharks
- Bichirs
- Sturgeons
- Gars and bowfins
- Teleosts, which include most familiar modern fish
- Lobe-finned fishes, including coelacanths
Teleosts make up the overwhelming majority of living fish species. FishBase’s February 2026 summary listed 34,982 extant teleost species out of 36,535 extant fish species worldwide. The same summary listed 1,294 sharks and rays and 58 chimaeras.
If you want to identify the fish you see while traveling, snorkeling, or visiting an aquarium, a marine fish identification book can be more useful than a worldwide species total. Regional guides cover selected coastlines or reef systems—not all 18,000 marine fish—but they usually provide photographs, range maps, habitat information, and distinguishing features.
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How many marine fish species have been described?
| Source and date | Reported figure | What it represents |
|---|---|---|
| FishBase, February 2026 | 18,080 | Fish species in marine, marine-and-brackish, or brackish-only habitat categories |
| Eschmeyer’s Catalog of Fishes, July 7, 2026 | About 18,371 by calculation | 37,678 valid fish species minus 19,307 species tagged as freshwater |
The FishBase figure is the clearest direct count for this question. Eschmeyer’s figure is a useful cross-check, but it is not a direct marine-only total. It is an inference based on subtracting freshwater-tagged species from the catalog’s worldwide total. Habitat labels, database structures, taxonomic decisions, and update schedules differ between the two resources.
For that reason, the most accurate general-audience wording is: scientists have described roughly 18,000 species of marine fish.
How many fish species are there worldwide?
There are roughly 36,500 to 37,700 currently recognized fish species worldwide, depending on the database and its counting rules.
- FishBase: 36,535 extant fish species in February 2026.
- Eschmeyer’s Catalog of Fishes: 37,678 valid fish species on July 7, 2026.
A difference of more than 1,000 species does not necessarily mean that one source is wrong. The databases may differ in how they handle synonyms, recently proposed species, disputed classifications, extinct or extant categories, and the timing of updates. They are separate taxonomic references, not two readings from one standardized census.
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Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Older articles often quote totals of 20,000 or 25,000 fish species. Those numbers may have been reasonable historical estimates or simplified explanations at the time, but they should not be treated as the best current totals. Fish classification and species discovery have moved the recognized total substantially higher.
Why isn’t there one fixed number?
New species are still being discovered
Fish species are found in places that are difficult to survey, including deep water, caves, remote reefs, polar seas, and poorly studied coastal habitats. Eschmeyer’s Catalog of Fishes recorded 408 new fish species in 2025 and 174 more through its July 7, 2026 update. It recorded 7,822 new fish species from 2007 through 2026, including 4,884 freshwater species.
These numbers show that the catalog is still growing. They do not, however, tell us exactly how many undescribed marine fish remain. The number of species formally described in a year depends not only on discoveries but also on collecting, laboratory work, funding, taxonomic expertise, and publication.
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Taxonomists revise existing classifications
A fish that was once considered one species may later be divided into several species after researchers compare DNA, anatomy, behavior, calls, geographic distribution, or reproductive compatibility. This is called a species split.
The opposite can happen too. Two named species may turn out to be the same species, in which case one name may become a synonym of the other. Revisions can also move a fish into a different genus or change how a database records its habitat.
As a result, a changing total does not mean scientists are merely guessing. It reflects an active process of testing and improving the classification of life.
Different sources count different categories
“Marine fish” can mean fish that live only in seawater, or it can include species that use both seawater and freshwater. FishBase’s marine total includes species classified as marine only, marine and brackish, or brackish only. It also separately listed 782 diadromous species—fish that migrate between marine and freshwater environments.
That matters for animals such as salmon and eels, whose life cycles can span very different environments. It also matters for fish found in estuaries, lagoons, tidal rivers, and other places where salt and fresh water mix.
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Therefore, “18,080 marine fish species” should not be interpreted as meaning that every one spends its entire life in the open ocean. It is a database category covering fish associated with marine or brackish habitats.
Are all of these fish found in the open ocean?
No. Marine habitats include much more than deep offshore water. The count can include fish from:
- Coral and rocky reefs
- Continental shelves
- Open-ocean waters
- Deep-sea habitats
- Mangrove forests
- Seagrass meadows and coastal shallows
- Estuaries and other brackish environments
Some species are strongly tied to salt water, while others tolerate changing salinity or migrate between habitats. The exact answer changes depending on whether the question means “fish that use any marine habitat” or “fish that live exclusively in the ocean.” The first interpretation is the one supported most clearly by the current FishBase count.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How many ocean species are still undiscovered?
More ocean species exist than have been formally described, but scientists cannot currently give a reliable fish-only total for the undiscovered remainder.
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That estimate applies to all ocean life, not fish alone. It would be misleading to turn it into a precise estimate of undiscovered fish without a separate, well-supported model. The defensible conclusion is simply that the roughly 18,000 described marine fish species are only the documented portion of the ocean’s fish diversity.
What share of ocean biodiversity is fish?
Fish represent a small part of total ocean biodiversity. The ocean also contains mammals, reptiles, birds, mollusks, crustaceans, corals, worms, jellyfish, sponges, algae, microscopic animals, fungi, and many other forms of life.
A 2011 study estimated approximately 2.2 million marine eukaryotic species overall. That was a model-based estimate with substantial uncertainty and included all marine eukaryotic life—not just animals and not just fish. Because the total number of ocean species remains uncertain, there is no single fixed percentage that can accurately describe the share made up by fish.
The reliable comparison is qualitative: roughly 18,000 described marine fish species make up only a fraction of the ocean’s total biological diversity.
What is the best answer to the question?
If you need one number, say about 18,000 described marine fish species. If you need the precise database figure, FishBase reported 18,080 in February 2026.
Add the qualification that the total changes as researchers describe new species and revise existing classifications. Also remember that this count includes fish associated with marine and brackish habitats, so it is broader than a count of species that live exclusively in the open ocean.
Frequently Asked Questions
How many different types of fish are in the ocean?
The best current general answer is about 18,000 described marine fish species. FishBase reported 18,080 species in marine, marine-and-brackish, or brackish-only habitat categories in February 2026.
Does the marine fish total include only fish that live in the open ocean?
No. The count includes fish associated with marine and brackish habitats, including coastal and estuarine environments. Some fish also migrate between freshwater and salt water.
How many fish species are there in the world?
FishBase listed 36,535 extant fish species worldwide in February 2026. Eschmeyer’s Catalog of Fishes listed 37,678 valid species on July 7, 2026. The difference reflects different databases, update dates, and taxonomic rules.
How many undiscovered fish species are in the ocean?
No reliable fish-only estimate is available. Estimates of 700,000 to 1 million ocean species refer to all ocean life, not specifically to fish.
The Bottom Line
Bottom line: Scientists have described about 18,000 marine fish species—18,080 in FishBase’s February 2026 count. The real number of fish species that exist is higher, and the total will continue to change as new fish are discovered and classifications are revised.
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