--- title: "How many fish are there in the sea? somewhere between 3 trilli" description: "somewhere between 3 trillion and 100 trillion — nobody knows How the figure is estimated, how confident it is, and what makes the scale graspable." url: https://atoneplace.net/how-many/fish-in-the-sea/ site: "At One Place" --- # How many fish are there in the sea? **How many fish are there in the sea?: somewhere between 3 trillion and 100 trillion — nobody knows** Bristlemouths of the genus Cyclothone are probably the most numerous vertebrates on Earth, quite possibly outnumbering every other fish combined, and almost nobody has heard of them. This is the entry on this page with the worst-known answer, and pretending otherwise would be dishonest. The commonly repeated figure of 3.5 trillion has no strong provenance. What is measured is biomass rather than headcount: mesopelagic fish — the small lanternfish and bristlemouths of the twilight zone — were revised upward around 2014 from about 1 billion tonnes to perhaps 10 billion tonnes on the strength of better acoustic surveys, a tenfold change in a single decade. Divide an uncertain biomass by an uncertain average fish mass and the uncertainty compounds. ## How the figure is arrived at Ship-mounted echosounders measure how strongly the water column scatters sound; that scattering is converted to biomass using a target-strength model for fish swim bladders. The swim-bladder assumption is where the tenfold revision came from. Trawl catches calibrate the acoustic figures but under-sample fast-swimming fish badly. ## How confident it is - **Low estimate:** 3,000,000,000,000 - **High estimate:** 100,000,000,000,000 - **Spread:** 33.3× between the bounds ## Other living things and the natural world counts - [How many people are there in the world?](https://atoneplace.net/how-many/people-alive-right-now/) — about 8.2 billion - [How many grains of sand are there on Earth?](https://atoneplace.net/how-many/grains-of-sand-on-earth/) — roughly 7.5 quintillion on the world's beaches - [How many ants are there in the world?](https://atoneplace.net/how-many/ants-on-earth/) — about 20 quadrillion - [How many trees are there in the world?](https://atoneplace.net/how-many/trees-on-earth/) — about 3 trillion - [How many insects are there?](https://atoneplace.net/how-many/insects-on-earth/) — about 10 quintillion - [How many species are there?](https://atoneplace.net/how-many/species-on-earth/) — about 8.7 million - [How many people have ever lived?](https://atoneplace.net/how-many/people-who-have-ever-lived/) — about 117 billion - [How many drops of water are there in the ocean?](https://atoneplace.net/how-many/drops-of-water-in-the-ocean/) — about 27 septillion - [How many species are endangered?](https://atoneplace.net/how-many/endangered-species/) — more than 45,000 assessed as threatened - [How many bees are there in the world?](https://atoneplace.net/how-many/bees-in-the-world/) — roughly 2 trillion managed honey bees - [How many birds are there in the world?](https://atoneplace.net/how-many/birds-in-the-world/) — about 50 billion wild birds - [How many bacteria are there on Earth?](https://atoneplace.net/how-many/bacteria-on-earth/) — about 5 nonillion - [How many earthquakes are there each year?](https://atoneplace.net/how-many/earthquakes-a-year/) — about 20,000 located a year — around 55 a day - [How many chickens are there in the world?](https://atoneplace.net/how-many/chickens-in-the-world/) — about 26 billion alive at any moment ## Common questions ### How many fish are there in the sea? somewhere between 3 trillion and 100 trillion — nobody knows ### How is that estimated? Ship-mounted echosounders measure how strongly the water column scatters sound; that scattering is converted to biomass using a target-strength model for fish swim bladders. The swim-bladder assumption is where the tenfold revision came from. Trawl catches calibrate the acoustic figures but under-sample fast-swimming fish badly. ## Related pages - [How many people are there in the world?](https://atoneplace.net/how-many/people-alive-right-now/) - [How many grains of sand are there on Earth?](https://atoneplace.net/how-many/grains-of-sand-on-earth/) - [How many ants are there in the world?](https://atoneplace.net/how-many/ants-on-earth/) - [How many trees are there in the world?](https://atoneplace.net/how-many/trees-on-earth/) - [How many insects are there?](https://atoneplace.net/how-many/insects-on-earth/) - [How many species are there?](https://atoneplace.net/how-many/species-on-earth/) - [How many people have ever lived?](https://atoneplace.net/how-many/people-who-have-ever-lived/) - [How many drops of water are there in the ocean?](https://atoneplace.net/how-many/drops-of-water-in-the-ocean/) - [How many stars are there in the universe?](https://atoneplace.net/how-many/stars-in-the-universe/) - [How many countries are there in the world?](https://atoneplace.net/how-many/countries/) - [How many bones are in the human body?](https://atoneplace.net/how-many/bones-in-the-human-body/) - [How many stars are there in the Milky Way?](https://atoneplace.net/how-many/stars-in-the-milky-way/) - [How many atoms are there in the universe?](https://atoneplace.net/how-many/atoms-in-the-universe/) - [How many galaxies are there?](https://atoneplace.net/how-many/galaxies-in-the-universe/) ## Sources - Typical range compiled from manufacturer specifications — At One Place (/about/)