SUBJECT : Facts about fishes 

 1. How many fish species are there?

The most often quoted estimate of the number of fish species is 20,000. There may be as many as 20,000 more.


2. What's the world's largest fish?

The whale shark is the largest fish.

The largest fish in the world ... is actually a shark. Specifically, the whale shark, which grows to more than 50 feet long and may weigh several tons. The second largest is the basking shark, which can measure 35 to 40 feet long.


3. What's the world's smallest fish?

The smallest fish is the tiny goby, which lives in the Philippines. It rarely grows longer than half an inch at adulthood, yet is so abundant it supports a fishery.


4. What's the most common fish in the ocean?

The most common fish is any of the species of a deepwater fish sometimes called a "bristle mouth." The fish is about the size of a small minnow. It is caught at 500 meters or deeper all over the world.


5. What are the oldest fish in the world?

The oldest fish-like animals are those with sucking mouths, like lampreys and hagfish. They stopped evolving before the development of biting jaws.

Zoologists study these bottom-dwelling fish because some parts of their bodies can help to explain evolution from low to advanced life forms.

Bluefish otoliths


6. How can you tell a fish's age?

Scientists can figure out how old a fish is by counting growth rings on its scales or its ear bones (called "otoliths"). The rings mark seasonal changes in fish growth, like the annual rings in tree trunks.

Otoliths grow like pearls, but the added material changes color depending on the season. The summer ring is whiter and the winter ring is thinner and more translucent.

In scales, a series of fine rings appear as the scale grows. In summer the rings are wider apart. In winter the rings are closer together, because the fish grow more slowly. Each pair of rings indicates one year.


7. How long do fish live?

The orange roughy lives more than 100 years. In the Northwest Atlantic, the longest-lived fish is the Acadian redfish, which can live past 40 years. How long a fish lives depends on its species.


8. Do fish breathe air?

Fish breathe oxygen, not air. Their gills contain a network of fine blood vessels that diffuse the oxygen throughout the fish's membranes.


9. Do fish sleep?

The dictionary defines sleep as a recurrent period of rest in which the nervous system is inactive, the eyes closed. Most fish don't have eyelids (except for sharks). Also, a great many fish live nearly motionless lives. But most fish rest. Some float in place, some wedge themselves into a spot in the mud or the coral, some even build themselves a nest. They are still alert for danger, but they are also "sleeping."


10. How do fish swim?

Lined seahorse swimming in vertical position

Fish swim primarily by contracting bands of muscles in sequence on alternate sides of the body. This whips the tail very rapidly from side to side in a sculling motion. Vertical fins are used mainly for stabilization. Paired pectoral and pelvic fins are used primarily for stability when a fish hovers. Sometimes fish might use them to aid rapid forward motion.

Tunas and tuna-like fish, billfish, and certain sharks are the speed champions. They can reach 50 miles per hour in short bursts. Sustained swimming speeds generally range from about 5 to 10 miles per hour among strong swimmers.

A number of fish species can swim backwards, but usually don't. Those that can are mostly members of one of the eel families.

Most fish swim in the horizontal position. The sea horse is among the exceptions. Another is the shrimp fish of the Indian Ocean, which congregates in schools of several individuals. It swims vertically, its long tube-like snout pointing directly upward. A catfish that lives in the Nile and other African rivers also swims in the vertical posture. Many kinds of midwater deepsea fish swim or rest vertically.


11. Do fish chew their food?

Fish would suffocate if they tried to chew their food. Chewing would interfere with the passage of water over the gills, necessary for obtaining oxygen. 

  • Carnivorous fish like sharks use their sharp teeth to seize and hold prey while swallowing it whole or in large pieces. 
  • Bottom dwellers such as rays are equipped with large flat teeth that crush the shellfish they consume. 
  • Herbivorous fish (grazers) often lack jaw teeth, but have tooth-like grinding mills in their throats, called pharyngeal teeth.


12. Are all fish edible?

Most kinds of fish encountered by anglers are edible. The organs of some species are always poisonous to man. Fish can become toxic because of elements in their diets.


13. Is there much salt in fish?

More than 240 species contain so little salt that doctors recommend them in salt-free diets. Shark meat is salty—as salty as the sea the shark lives in.

14. Why do fish sometimes have a strong odor?

For most species, truly fresh fish is almost odorless. Fish begin to smell "fishy" when it starts to deteriorate, usually when it isn't stored or preserved correctly.


15. Will the fish I catch and release die anyway?

Looking into the mouth of an Atlantic cod

If fish caught with artificial lures are handled carefully, most will survive. Many factors influence survival after release:

The fish was already stressed before being caught, for instance because of spawning or high water temperatures.

The fish is "played" for a long time and is exhausted before release.

The fish is hooked through a sensitive area such as the gills or the eye, or deeply in the throat (which is more likely when using bait).

The fish is handled roughly; for example, squeezed strongly or held out of water too long.

The fish is caught in deeper water.

If a fish seems to be having difficulty after unhooking, cradle it gently in the water until it regains its equilibrium and swims off under its own power.