Amazing Facts About Fish You Probably Didn't Know

Fish quietly hold some of the animal kingdom's most extreme records the oldest known vertebrate, the strongest electrical discharge ever measured, and a body plan diverse enough to span more than 37,700 documented species. Here are some of the most interesting facts about fish worth knowing, organized around the records, the biology, and the myths worth retiring.

The Records Fish Hold

The Greenland shark record is especially striking: females aren't thought to reach sexual maturity until around 150 years old, meaning a shark alive today could have been born before the United States existed.

Biology That Sounds Made Up (But Isn't)

Sex Changing Fish

Clownfish are protandrous every individual starts life male, and the dominant fish in a group switches to female if the existing female dies. Many wrasse species run the reverse pattern, starting female and switching to male, an adaptation tied closely to social hierarchy rather than age alone.

Whole Body Taste Buds

Catfish don't just taste with their mouths taste buds cover their entire body, including their barbels, letting them sense food in water too murky to see through.

Colorless Blood

Antarctic icefish have no hemoglobin at all, giving them clear blood. It works because their frigid Southern Ocean habitat holds far more dissolved oxygen than warmer waters, letting oxygen travel through plasma alone.

New Species Are Still Being Found

Fish diversity isn't a closed book. In 2025 alone, taxonomists formally described 309 new freshwater fish species the third highest annual count since scientific record keeping began in 1758 found everywhere from Chinese limestone caves to Congolese rain puddles. Asia led the discoveries with 165 new species, followed by South America with 91.

One Myth Worth Retiring

The idea that goldfish only remember things for three seconds doesn't hold up. Research has shown goldfish can retain learned associations, like feeding times or maze routes, for months closer to the memory span of many small mammals than the joke usually implies.

FAQs

Which fish lives the longest?

The Greenland shark is the longest lived vertebrate known to science, with radiocarbon dating estimating a lifespan of roughly 272 to 500 years.

What is the strongest electric shock a fish can produce?

Electrophorus voltai, an electric eel species identified in 2019, can discharge up to 860 volts, the highest recorded voltage from any living animal.

How many fish species have scientists documented?

More than 37,700 valid fish species are documented in Eschmeyer's Catalog of Fishes, and new species are still being found 309 new freshwater species were described in 2025 alone.

Do any fish change sex naturally?

Yes clownfish start life male and can switch to female, while many wrasse species do the reverse, both changes driven by social group structure rather than age.

Is it true goldfish forget things after 3 seconds?

No, that's a myth. Goldfish have been shown to retain learned information, such as feeding schedules and maze routes, for several months.

Conclusion

Between a shark that can outlive a country's entire history and an eel packing more voltage than a wall outlet, fish are one of the most record holding groups in the animal kingdom and with new species still being discovered every year, there's clearly more to learn.

Want the science behind how these species get studied? Read our guide to fisheries science, or check out our species profile on Atlantic cod (Gadus morhua), another species with a record of its own extreme fecundity.