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Clear out junk files and repair common Windows errorsFree Scan →Scan for outdated or missing drivers - takes under a minuteDriver Scan →Repair Windows errors before they cause bigger problemsFix Now →A 2013 review reported 3,356 described deep-sea fish species by the first decade of the 21st century. That is a useful published benchmark, not an exact count of species alive or known today. There is no single agreed depth boundary for “deep sea,” and different definitions can include different fish.
Why there is no single current total
A species count depends partly on what researchers mean by “deep sea.” The World Register of Deep-Sea Species (WoRDSS) says there is no single definition. Its database includes records sampled at depths greater than 500 metres, covering both pelagic fish (those living in the water column) and benthic fish (those living on or near the seafloor). A species recorded below 500 metres may be included even if it also occurs in shallower water. This is a database rule, not a universal biological boundary. WoRDSS database information
Other conventions draw the line elsewhere. Traditional classifications often use the continental shelf break, at approximately 200 metres, while other schemes use different limits. The Food and Agriculture Organization (FAO) notes that there is no commonly agreed definition of deep-sea fishes. In a fisheries context, it describes them as species inhabiting continental-slope waters and beyond that are exploited by fisheries there. Vertical migrations and changes in habitat between life stages also make a single depth cutoff difficult to apply. FAO overview of deep-sea fisheries
What the 3,356-species figure includes
Priede and Froese’s 2013 review, Colonization of the deep sea by fishes, reported 3,356 described deep-sea fish species by the first decade of the 21st century. The review divided them into two ecological groups:
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| Group | Species reported | Meaning |
|---|---|---|
| Bathydemersal | 2,081 | Fish associated with the deep seafloor. |
| Bathypelagic | 1,275 | Fish living in the deep water column. |
| Total | 3,356 | The two reported groups combined. |
Those figures add up to the review’s stated total. They are a historical count of described fish species—not a count of every deep-sea animal, an estimate of undiscovered fish, or a live tally of currently recognized species. Priede and Froese’s 2013 review
What other ocean figures can—and cannot—tell you
NOAA’s National Ocean Service cites an estimate that 91% of ocean species have yet to be classified. That estimate concerns ocean species broadly; it does not give the number of deep-sea fish species, so it cannot be used to revise or extrapolate the 3,356 figure. NOAA on the number of ocean species
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A record for the deepest observed fish answers a different question from a species count. NOAA Ocean Exploration reports a deepest confirmed filmed fish sighting of a snailfish at 8,336 metres. That establishes a reported depth record, not how many kinds of deep-sea fish exist. NOAA Ocean Exploration on the deepest fish
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How to interpret a deep-sea fish count
- Check the depth definition: a cutoff near 200 metres and WoRDSS’s sample-depth criterion of greater than 500 metres do not describe identical sets of fish.
- Check which habitats are included: the 2013 review separates seafloor-associated bathydemersal species from water-column bathypelagic species.
- Check the date and scope: 3,356 is the review’s described-species benchmark for the first decade of the 21st century, not a present-day census.
For background on deep-sea fish definitions and biology, see Imants G. Priede’s specialist book Deep-Sea Fishes. Cambridge University Press: Deep-Sea Fishes
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