Last updated on June 28th, 2022
Fish are cold-blooded vertebrates that live wholly in water. They have no limbs. Instead, they live, move (swim), and breathe thanks to the unique combination of their tail, fins, gills, and scales fitted to their elongated and limbless bodies.
Fish comes in all sizes, shapes, and forms. They can also be found in different bodies of water like the ocean, rivers, lakes, and ponds. Whatever differences there are that may exist, however, there are general features that define them and make them who they are.
Like any other animal classification, fish must feed (or eat) to stay alive. Generally, fish need some form of meat in their diet. For smaller fish, this is often sourced from worms, smaller fish, or insects. For larger fish, other fish smaller than itself, smaller mammals, and even birds may become primary food sources. Of course, whatever food sources they primarily enjoy, the same must be consistently available for them to subsist from the same.
With these interesting facts about fish let us learn about their evolution, anatomy, behaviour and more.
Distinction and Evolution
1. Fish Traits
Fishes come in all shapes and sizes, but they have a few common denominators: they live in water, they have a backbone, and they use gills for breathing.
2. Fossil Records
Fossil records show that fishes have been around for over 500 million years, beginning with the Cambrian Explosion — way before the dinosaurs ever existed.
3. Number of Species
As of 2020, there were 34,000 known fish species around world. That’s more than the number of species in all other vertebrates: birds, reptiles, mammals, and amphibians combined.
4. Not a Fish
If we’re going to be strict about it, jellyfish and starfish are not really fish because they don’t have a backbone. As a correction, many public aquaria are now using the terms “sea jellies” and “sea stars”.
5. Age Analysis
To find out how old a fish is, scientists count the growth rings on its ear bones or its scales. These mark the passing of the seasons with distinct colors and thickness.
6. Avoiding Sunburn
Fish need shelter or a way to move deeper underwater to avoid excessive sun exposure. If not, they can get sunburn as well.
7. Smelly Fish
Don’t be too hard on fish. Contrary to their reputation, fresh fish is almost odorless. The strong smell only develops due to improper storage, as a sign of deterioration.
8. Mouth Shapes
Fish mouths point in the direction of their food. Bass use their upward-facing mouths to creep up to their prey. Catfish have downward-facing mouths to feed on the sea floor. Barracudas use their forward-facing mouths to hunt everywhere.
9. Mountain Fish
Fish can be found in almost all bodies of water, even in high mountain streams. Examples of fish at high elevation include the char, trout, loach, and gudgeon.
10. Deep Ocean Fish
The deepest fish habitat is the hadal zone located 6,000 to 11,000 meters below sea level. Here you can find cusk-eels, snailfish, and pearlfish. For perspective, the peak of Mount Everest is 8,849 meters high.
11. Useful Fish Slime
Fish slime may seem gross, but it’s a useful coating that makes them slippery, allowing them to move fast through water and avoid predators. The slime can also cover wounds to prevent infection.
12. Natural Armor
Fish are like sea knights that grow their own armors. Their scales protect fish from predators and parasites. These also prevent injuries like cuts.
13. Built-in Radar
Many species of fish have a powerful sense organ called the lateral line running across their body. It can detect motion in the water, allowing them to hunt prey, avoid predators, and navigate in the dark.
14. Fish Can’t Blink
Most fish don’t have eyelids, so they can’t blink. It’s hard to know whether they are relaxed or startled because they never change their expression.
15. Taste Buds
Catfish have a more refined sense of flavor than humans. Our 10,000 taste buds may seem like a lot, but catfish can have as many as 175,000. This helps them find the exact location of their next meal.
16. Fish Brain
Fish have small brains in comparison with other animals. For example, their brain is roughly one-fifteenth of a bird with the same body size. However, they exhibit surprising signs of intelligence.
17. Breathing as a Fish
Most fish breathe through gills, which are thin sheets of tissue with a network of blood vessels. These absorb dissolved oxygen from the water into the blood and expel carbon dioxide as waste.
18. Cold-blooded Creatures
Most fish are ectothermic or cold-blooded, just like their distant relatives: reptiles and amphibians. They lean on the water’s ambient temperature to fuel their metabolism.
Tunas, barracudas, swordfish, and mackerels are exceptions to the rule. Tunas can maintain a body temperature of 90 degrees Fahrenheit despite swimming in 45-degree waters.
20. Swim Bladders
Fish typically stay at a certain depth, because the available food changes if they go up or down. Their special swim bladder helps them maintain their desired buoyancy without using a lot of energy.
21. Longest Lifespan
The orange roughy stays true to its name. It can live for up to 150 years, putting it up there as one of the longest-living fishes that exist today.
22. Fastest Fishes
The sailfish can swim at a whopping speed of 68mph. The marlin is a far second at a top speed of only 50mph. Meanwhile, tunas can swim up to 47mph.
23. Largest Fish
The biggest fish in the world is the whale shark. Adults can reach 50 feet in length and weigh several tons. Also worth mentioning is the basking shark which can grow up to 40 feet.
24. Slowest Fish
The unfortunate title of being the slowest fish belongs to the oddly shaped seahorse. It can only move at a rate of 0.01 mph.
25. Smallest Fish
An adult male photocorynus spiniceps is only 6.2mm long. It is much smaller than the females which are 46mm long. They live at a depth of 1,425 meters in the Philippine Sea.
26. Best in Bioluminescence
The hatchet fish just keeps on shining. This deep-sea creature evolved light-emitting organs to conceal their shadows and avoid predators.
27. Most Common Fish
The “bristle mouth” will be right there, wherever you are. You can find this deep-water fish all over the world around 500 meters under the surface.
28. Loudest Fish
Make some noise for the croaker. It’s the loudest fish known to man with vocalizations that can reach 177 decibels. Males sound like an underwater machine gun when singing their mating songs.
29. Stickiest Fish
The Northern Clingfish lives up to its name with an adhesive force that is 80 to 230 times greater than its bodyweight. Its belly has a modified suction cup that lets it stick to rocks and avoid getting washed away by strong currents.
30. Coldest Habitat
The Antarctic ice fish has a natural antifreeze substance in their blood, allowing them to live in subzero waters.
31. A Timid Piranha
Many people fear them, but the red-bellied piranhas of the Amazon are actually timid scavengers. They are unlikely to harm humans, preferring insects, worms, crustaceans, and other fish.
32. Mucus Blanket
There is nothing better than a nice warm blanket. Parrot fish cover themselves in a blanket made of their own mucus for protection. It stops blood-sucking parasites from ruining their sleep.
33. Fish Out of Water
The fascinating West African lungfish can breathe with both gills and lungs, allowing them to survive on land. During dry summers, they burrow in mud and stay dormant until the rainy season. They digest their own tail muscles to survive this period.
34. Backstroke Specialists
Only a few fishes swim backwards regularly. Eels take the crown as the backstroke specialist. The triggerfish and blue gill sunfish are great at it, as well.
35. Handy Fish
They may not be as sophisticated as humans, but some fish are smart enough to use tools. For example, the orange-dotted tuskfish has been filmed smashing mollusks on rocks to break the shell and get the meat.
36. Amazing Anglerfish
When anglerfish hunt, they use a glowing antler with a piece of meat like a fishing pole. In a case of extreme mating, male and female fuse to become a single organism. Females can absorb 6 or more males in their lifetime.
37. Salmon’s Journey
Salmon are born in freshwater but live at bountiful seas, after an epic thousand-mile journey. Upon maturity, they go back to spawn. They develop muscles strong enough to swim against rapids and move up small waterfalls.
38. Gulping Air
The spotted climbing perch can gulp oxygen in the air as it crawls over land, using its pectoral fins. It can survive out of water for weeks.
39. First Psychedelic Drug
Ancient Romans used the salema porgy for a different kind of fishing trip. Its Arabic name means “fish that makes dreams”. The small fish with gold-blue stripes has toxins that can invoke vivid hallucinations.
40. Flatfish Transformation
Halibut and other flatfish aren’t born flat. They start out looking like a normal fish. After 2 months, their skulls shift and pull both eyes on one side. Their bodies flatten, their color changes, and they start eating other fish instead of plankton.
41. How Fish Sleep
Fish can’t close their eyes to sleep, but they can restore their energy with their own way of sleeping. Some float in place, while others wedge themselves in corals to save energy.
42. Creating Artworks
Male pufferfish can make large patterns on the sand by flapping its fins. It may even decorate it with shells to attract females — quite the romantic gesture.
Fish may not have vocal cords, but they can use other body parts to communicate. They might grind teeth, rattle bones, or vibrate muscles against their swim bladder to generate sound.
Most fish fertilize their eggs externally. Females can expel thousands of eggs at a time. Males also release their sperm in the water and let nature run its course.
45. Fish Can Recognize Faces
A study showed that pet fish can distinguish a familiar human face from other faces with good accuracy. The research used archerfish which could indicate choices by shooting water one way or the other.
Fishkeeping Across the Ages
46. Early Fishkeeping in Asia
About 2,000 years ago in Japan, selective carp breeding resulted in the domestication of koi fish. Later, the Hongwu Emperor of China built his own porcelain company to create large tubs for goldfish.
47. Rich Roman Pets
Wealthy Romans were known to keep marine pets in their palatial homes. Many had saltwater pools with lampreys, mullets, and other fish. They were dubbed as the “Piscinarii” or fish breeders.
48. Medieval Fish Ponds
In Europe, most large estates and monasteries had their own pools of carp for food. Several religious feast days forbade the consumption of meat, and fish was the most viable alternative.
49. Aquarium Invention
In 1832, the French marine biologist Jeanne Villepreux-Power created the first aquarium. She used it to conduct a systematic study of marine animals.
50. First Public Aquaria
On May 1853, the first public aquarium called “The Fish House” opened in the London Zoo. Famous showman P.T. Barnum quickly followed with his own aquarium three years later in New York City.
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