About 18,000 recognized marine fish species live in the sea. FishBase’s June 2026 breakdown lists 18,155 in its marine category; this is a dated count of recognized species, not a count of individual fish or a guarantee that every species has been discovered and described.
“Types” is an informal way to say species. Counts can differ depending on the database, update date, taxonomic decisions, and how habitat categories are defined.
Key takeaways
- FishBase listed 18,155 marine fish species in June 2026, a reasonable basis for saying “about 18,000.”
- FishBase listed 36,761 extant fish species overall: 18,155 marine, 17,817 freshwater, and 788 diadromous.
- FishBase’s marine category includes marine-only, marine-and-brackish, and brackish-only fish.
- NOAA Fisheries’ often-quoted figure of 20,000 is a broad estimate, not the same metric as FishBase’s dated marine-category count.
- The number of individual fish in the ocean is a different question from the number of recognized species.
How many types of fish are in the sea?
FishBase’s June 2026 overview lists 18,155 recognized species in its marine category. In everyday language, “types” usually means species; this count is a database snapshot, not a permanent total.
The figure does not count individual fish swimming in the ocean, and it does not establish how many species remain undiscovered or undescribed.
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What is the current number of marine fish species?
FishBase lists 18,155 marine fish species in its June 2026 breakdown. Its marine category includes marine-only, marine-and-brackish, and brackish-only fish. It is best to state the source and date alongside the precise figure.
FishBase’s June 2026 overview separates its extant fish species into these categories:
| FishBase category | Recognized species | What the category means |
|---|---|---|
| Marine | 18,155 | Includes marine-only, marine-and-brackish, and brackish-only fish |
| Freshwater | 17,817 | Fish assigned to FishBase’s freshwater category, which includes freshwater and brackish categories |
| Diadromous | 788 | Fish that move between marine and freshwater environments |
| All extant fish in the overview | 36,761 | The FishBase total across its reported categories |
See the FishBase species report for its category totals. Database totals can change as records and classifications are updated.
Why do fish databases report different totals?
Fish databases can report different totals because they may use different update dates, taxonomic decisions, and category conventions. Species may be newly described, combined after review, split into several species, or assigned to different categories.
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It is important to compare like with like: the date, accepted-species rule, and habitat scope all matter. For example, WoRMS distinguishes accepted marine species from all marine species names, which include synonyms. Its marine-organism totals should not be presented as fish counts.
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WoRMS illustrates why a database’s metric and scope should be checked before comparing totals.
Are there 20,000 species of fish in the sea?
“About 20,000” is a commonly quoted broad estimate, but it is not the same measure as FishBase’s dated count of marine-category species. NOAA Fisheries says, “The most often quoted estimate of the number of fish species is 20,000. There may be as many as 20,000 more.” That statement does not specify a modern marine-only database category.
For a dated marine-category answer, FishBase lists 18,155 species in June 2026. For a general approximation, “about 18,000 marine fish species” is a clear summary of that snapshot.
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Does the marine fish count include every fish species in the ocean?
No. A database count records recognized species; it does not establish the total number of species that exist or remain undescribed. During the Census of Marine Life, more than 1,200 new marine species were formally described, and thousands more awaited formal description at the time, according to NOAA’s National Ocean Service.
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That historical example concerns marine species broadly, not just fish. It should not be used to calculate a separate total of undiscovered fish species. As researchers study poorly sampled habitats and revise classifications, recognized fish totals can change.
See NOAA’s National Ocean Service material on ocean exploration for the Census context.
How many fish species are there in the whole world?
FishBase listed 36,761 extant fish species worldwide in its June 2026 overview. That total includes marine, freshwater, and diadromous categories: 18,155 marine, 17,817 freshwater, and 788 diadromous species.
The worldwide total should not be substituted for the answer to how many types of fish are in the sea. FishBase’s marine-category figure is the relevant one for that question.
What is the difference between marine, freshwater, and diadromous fish?
Marine fish are assigned to FishBase’s marine category, freshwater fish to its freshwater category, and diadromous fish move between marine and freshwater environments. FishBase’s category definitions also include brackish-associated fish in its marine and freshwater groupings, so the labels are database conventions rather than perfectly exclusive descriptions of every fish’s life.
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These categories help explain why “all fish” and “fish in the sea” are different counts. Name the database when using its category totals.
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A species count helps explain biodiversity, but identifying a fish requires details such as its body shape, markings, habitat, and location. A regional marine fish field guide can help with identification; check that the guide covers the region where the fish was seen rather than treating it as a worldwide catalogue.
Why will the answer change over time?
The answer can change as new species are formally described and existing classifications are revised. Database totals are snapshots tied to a source and date, not permanent natural constants.
FishBase’s June 2026 figures are the dated snapshot used here. Recheck the database before using the precise count in a future update.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What is the shortest accurate answer?
About 18,000 recognized marine fish species are listed in FishBase’s June 2026 snapshot, specifically 18,155 in its marine category. The number can change as species are described and classifications are revised.
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FAQ
How many individual fish are in the ocean?
The FishBase count does not answer how many individual fish are alive in the ocean. Its 18,155 figure is a count of recognized species in a database category, not individual animals.
Why do some sources say there are 20,000 fish species?
NOAA Fisheries describes 20,000 as the most often quoted estimate and says there may be as many as 20,000 more. It is a broad estimate, not the same metric as FishBase’s June 2026 count of 18,155 in its marine category.
Does the count include every fish species in the sea?
No. It is a count of recognized species represented in a database, not a complete inventory of every species that may exist. NOAA’s Census of Marine Life summary notes that thousands of marine species awaited formal description at the time of the project.
How many fish species are there worldwide?
FishBase listed 36,761 extant fish species overall in June 2026, including marine, freshwater, and diadromous categories. The total is broader than the marine-category count.
The Bottom Line
About 18,000 recognized fish species are in FishBase’s marine category: the June 2026 count is 18,155. This is a dated species count, not the number of individual fish or all fish species that may exist.
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