50 Fun Facts About Fish You Probably Didn't Know

With more than 34,000 known species, fish are the most diverse group of vertebrates on Earth which means there's no shortage of genuinely wild fish fun facts once you start digging. Here are 50 fun facts about fish, covering speed and size records, bizarre behavior, strange adaptations, reproduction, and a few facts anglers in particular will appreciate.

Speed & Size Records

1. The sailfish is widely cited as the fastest fish in the ocean, with popular figures around 68 mph, though rigorous modern tracking studies suggest its actual sustained speed is considerably lower than that classic claim.
2. The whale shark is the largest fish alive, growing beyond 40 feet and weighing more than 15 tons, despite subsisting mostly on plankton.
3. The black marlin, a top game fishing target, has been tracked with burst speeds well over 40 mph, making it one of the hardest fighting fish an angler can hook.
4. Bluefin tuna can weigh over 1,000 pounds and are capable of explosive high speed bursts while chasing prey.
5. The Greenland shark is the longest living vertebrate known on Earth, with some individuals estimated to live beyond 270 years, and possibly past 500.
6. Sturgeon can live over 100 years and grow to enormous sizes, making them among the longest lived freshwater fish targeted by anglers.
7. Yelloweye rockfish, a prized deep water catch, can live well past 100 years one of the longest documented lifespans of any bony fish.
8. Ocean sunfish (Mola mola) can weigh over 2,000 pounds, ranking among the heaviest bony fish species in the world.
9. The smallest known fish species is a type of stout infantfish, with adults measuring under a centimeter long.
10. Flying fish can glide above the surface for distances beyond 600 feet using enlarged, wing like fins to escape predators and the occasional angler's boat deck.

Weird Behavior

11. Cleaner wrasses run "cleaning stations" on reefs where larger fish line up voluntarily to have parasites picked off, a genuine cooperative relationship rather than predation.
12. Archerfish spit precisely aimed jets of water to knock insects off overhanging branches, then eat them once they fall.
13. Clownfish coat themselves in protective mucus that makes them immune to the stinging cells of the sea anemones they shelter in.

Groupers and moray eels have been observed hunting cooperatively on reefs, with the grouper signaling the eel to flush prey out of tight crevices.

1. Salmon can return to the exact river they hatched in years earlier, largely by detecting that stream's unique chemical scent.
2. Mudskippers can breathe air and move across exposed mudflats using their fins almost like limbs.
3. Some catfish species have been documented beaching themselves briefly to snatch pigeons resting at the water's edge.
4. Electric eels generate shocks of several hundred volts using specialized cells along their body, enough to stun prey or deter predators.
5. Goldfish memory is far better than the popular "three second memory" myth suggests studies show they retain learned information for months.
6. Certain cichlid species have demonstrated the ability to distinguish individual human faces in laboratory studies.

Strange Adaptations

21. Antarctic icefish produce natural antifreeze proteins in their blood, preventing them from freezing solid in sub zero polar water.
22. The mangrove rivulus can survive out of water for weeks at a time, breathing through its skin while hiding in damp logs.
23. Lungfish survive extended droughts by burrowing into mud and breathing air directly through a modified lung like organ.
24. Several fish species, including certain wrasses and clownfish, can change sex during their lifetime depending on the social structure of their group.
25. The frogfish "walks" along the seafloor using its fins almost like legs rather than swimming through open water.
26. The hagfish defends itself by releasing enormous amounts of slime almost instantly when threatened, clogging the gills of would be predators.
27. Certain gobies can climb waterfalls, using suction cup like fins to grip wet rock as they move upstream.
28. Anglerfish produce their own light through bioluminescence, luring prey in the pitch black depths of the deep sea.
29. In some anglerfish species, the much smaller male permanently fuses to a female's body, surviving essentially as an attached sperm source for life.
30. The blobfish, frequently mocked online for its droopy surface appearance, looks far more ordinary in its natural deep sea habitat, where water pressure supports its gelatinous body.

Anatomy & Senses

31. Catfish don't just taste with their mouths taste buds cover their entire body, including their skin and fins.
32. Four eyed fish (Anableps) have eyes split into upper and lower halves, letting them see above and below the surface simultaneously.
33. Sharks have existed in some form for more than 400 million years older than trees.
34. Fish don't have eyelids the way mammals do, which is why it can look like they never blink, though many species do rest with reduced activity.
35. A fish's lateral line, a row of sensory organs along its sides, detects pressure changes and vibration in the water, effectively "feeling" nearby objects without touching them.
36. Seahorses have no stomach at all, digesting food so quickly that they must eat almost constantly to survive.
37. Pufferfish inflate by rapidly gulping large amounts of water, expanding to several times their normal size to deter predators.
38. Parrotfish have fused, beak like teeth strong enough to bite off chunks of coral, and a single parrotfish can generate hundreds of pounds of sand like waste a year from digested coral.
39. Some deep sea fish have nearly transparent bodies, an adaptation for avoiding predators in a habitat with almost no light to hide in.
40. A shark's skin is covered in tiny tooth like scales called dermal denticles, which reduce drag and improve swimming efficiency.

Reproduction, Family Life & Angling Notes

41. Seahorses are one of the only animal groups where the male carries developing offspring, in a specialized pouch, until they're born.
42. Rockfish species give birth to live young rather than laying eggs, a strategy called ovoviviparity shared across the entire rockfish family.
43. Salmon undertake one of the animal kingdom's most demanding migrations, swimming from ocean to freshwater rivers to spawn, sometimes traveling hundreds of miles against the current.
44. European eels migrate thousands of miles to the Sargasso Sea to spawn a journey scientists still only partially understand.
45. Some fish species release well over a million eggs in a single spawning event, though only a small fraction typically survive to adulthood.
46. Certain tilapia species are mouthbrooders, carrying fertilized eggs and even hatched fry inside their mouths to protect them from predators.
47. Bettas build bubble nests at the water's surface, where males guard fertilized eggs until they hatch.
48. Many rockfish and demersal reef species mature very late some not until well over a decade old which is exactly why so many carry strict catch and release regulations today.
49. Big game species like marlin and tuna are prized specifically because their size and strength make catching one a multi hour fight, not a quick reel in.
50. Fish diversity worldwide is staggering more than 34,000 recognized species make up roughly half of all known vertebrate species on Earth.

FAQ

What is the fastest fish in the world?

The sailfish is popularly cited as the fastest, with figures near 68 mph, though newer, more rigorous tracking studies suggest its true sustained speed is likely well below that classic number.

What is the biggest fish in the ocean?

The whale shark, which can exceed 40 feet in length and weigh more than 15 tons, despite feeding mostly on plankton rather than other fish.

What's the longest living fish?

The Greenland shark, with some individuals estimated to live beyond 270 years and possibly past 500 the longest living vertebrate known on Earth.

Do fish actually sleep?

Many rest, but because most fish lack eyelids, it can look like they never close their eyes they typically slow down and become less active rather than sleeping the way mammals do.

Can fish change sex?

Yes. Several species, including certain wrasses and clownfish, can change sex during their lifetime depending on the social structure of their group.

Why do so many game fish have strict catch limits?

Many prized species, including several rockfish and reef species, grow slowly and mature late, meaning their populations recover slowly from overfishing which is why regulations tend to be stricter for these species than for fast growing ones.

How many species of fish exist?

More than 34,000 recognized species, making fish the most diverse group of vertebrates on the planet.

Conclusion

From a shark that might outlive a small nation's history to an anglerfish that literally fuses to its mate, fish biology delivers stranger facts than most fiction. If any of these sparked your curiosity about a specific species, browse our Fish Species library for detailed identification and behavior guides.