Interesting Fish Facts for Curious Minds

Fish make up more than half of all known vertebrate species on Earth, and buried in that diversity are some genuinely strange biological records animals that outlive empires, generate more voltage than a wall socket, or don't settle on a sex until adulthood. Here's a collection of interesting facts about fish worth knowing, whether you're a student, an angler, or just fish curious.

Record Breaking Fish

• The Greenland shark is the longest living vertebrate known to science. Radiocarbon dating of eye lens tissue puts its lifespan between roughly 272 and 500 years, with one individual estimated at close to 392 years old meaning some Greenland sharks alive today were already swimming when the Mughal Empire ruled South Asia.
• Electric eels can generate up to 860 volts of electricity. A 2019 study identified a new species, Electrophorus voltai, capable of that record breaking discharge well above household electrical current and more than 30% higher than the previous record of 650 volts.
• The sailfish is widely cited as the fastest fish in the ocean, with burst speeds estimated up to around 68 mph (110 km/h) in short sprints, though exact top speed claims for fish remain difficult to measure precisely in the wild.

Strange and Surprising Biology

• Some fish change sex during their lifetime. Clownfish are protandrous, starting life as male and switching to female if the dominant female in their group dies; many wrasses do the reverse, starting female and becoming male.
• Catfish are covered in taste buds not just in the mouth, but across their entire body surface, including their whisker like barbels, letting them 'taste' the water around them to locate food in murky conditions.
• Antarctic icefish have clear, colorless blood. They lack hemoglobin entirely, relying on oxygen dissolved directly in their blood plasma, an adaptation that works only because the frigid Southern Ocean holds more dissolved oxygen than warmer water.

How Many Kinds of Fish Are There?

Fish are far more diverse than most people assume. Eschmeyer's Catalog of Fishes, the standard scientific reference, currently documents more than 37,700 valid fish species and the list keeps growing. In 2025 alone, taxonomists formally described 309 new freshwater fish species, the third highest annual total since record keeping began in 1758, discovered everywhere from limestone caves in China to seasonal wetlands in the Democratic Republic of Congo.

Fish Behavior Myths, Debunked

The popular claim that goldfish have a three second memory is a myth. Studies have shown goldfish can retain learned information for months, including remembering feeding schedules and navigating mazes they've encountered before a reminder that even the most "basic" pet fish are more cognitively capable than folklore suggests.

FAQs

What is the longest living fish?

The Greenland shark holds the record, with radiocarbon dating suggesting a lifespan of roughly 272 to 500 years, making it the longest living vertebrate known to science.

What fish produces the most electricity?

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

How many species of fish exist?

Eschmeyer's Catalog of Fishes currently documents more than 37,700 valid fish species, with new species still being discovered and described every year.

Can fish really change sex?

Yes species like clownfish and many wrasses can change sex during their lifetime, a natural adaptation tied to their social group structure and reproductive strategy.

Do goldfish really only have a 3 second memory?

No, this is a myth. Research has shown goldfish can retain learned information, such as feeding schedules and maze routes, for months at a time.

Conclusion

From centuries old sharks to eels that outshock a wall socket, the more than 37,700 known fish species hold some of the animal kingdom's most surprising records. These interesting fish facts are just a starting point the deeper science behind how these species evolved, survive, and get studied is where things get even more interesting.

Curious how scientists study species like these? Start with our guide to What Is Fisheries Science?, or read our deep dive on Atlantic cod (Gadus morhua), a species with its own record setting fecundity.