Home Fishing Tips & Advice How Many Fish Live in the Ocean?

How Many Fish Live in the Ocean?

The Census of Marine Life was established to identify and document information and discoveries pertaining to marine life. But to this date, there is no exact figure representing how many fish live in the ocean. Some estimations run over 3,500,000,000,000. However, since fish are always moving, hiding, reproducing, and declining in numbers, there is no definite certainty to any statistics.

Fish has always had an important role in human life since time immemorial.  It has served mankind in so many different ways. Nowadays, some are raised and cherished as pets, others are cultivated for trade, food, health ; skin care products.

The species is studied for medical and biological research, while others are nurtured ; trained for zoos and park attractions.  Let’s learn more about these wonderfully beautiful and invaluable creatures.

What Types of Fish are in the Ocean?

Not all aquatic animals are fish, because fish are sea creatures that are vertebrates (creatures with a spinal column). And the term “fish” is not a reference to just one group of these sea creatures, rather, it includes several different classifications.

In fact, of all the vertebrate animals, fish have the most variety of living classifications that can be found, which is approximated to be more than 32,000.

There are three major groups, and all these species are categorized based on their skeletons and mouth structure. The groupings are the Lampreys, the Cartilaginous, and the Bony Fish.

The Lampreys

These are known as Jawless, have bodies that are long and eel-like. But they are not eels. Lampreys are further divided into two categories, which are the parasitic and the non-parasitic.

The Cartilaginous

This group of fish take the name from their skeletal frame, which is composed of cartilage. But despite having an inner structure consisting only of cartilage, they still grow to very large sizes. This fish group include rays, skates, and sharks.

The Bony Fish

It is the largest and most familiar of these fish groups. It is also the most diverse of the groups, consisting of about ninety-five percent of all fish species found in salt and fresh waters.

As its name implies, the skeletal structure of these fish is made of bone. This fish group is further divided into two subgroups, the Ray-finned, and the Lobe-finned. Tuna, trouts, clownfish, catfish, and goldfish are a few examples of those that belong to this group.

How are Ocean Fish Different from Other Creatures?

Fish breathe differently

Fish need oxygen. But instead of getting it from the air above water, they breathe water. With the use of their gills, they are able to get all the oxygen they need from the water that they pull and pump into it. This is why aquariums are recommended with air pumps, so that your pet fish will have oxygen-rich water around them.

Some types of fish, though, can also breathe air, but only for a limited time. These types of fish have two categories: the ones that must breathe air periodically to stay alive, and the ones that do so only when they need to.

Among this second group, there are a number of species, like the Catfish, that usually venture into land to find other bodies of water that are better feeding grounds. The Mudskipper, though, is most probably the most able in this category, because it can stay and move about on land for several days.

Fish are cold-blooded

Being cold-blooded, they cannot adjust their own internal body temperature, they adapt to the same temperature as that of their environment.

Fish don’t have eyelids

Since they don’t have eyelids, they simply sleep with their eyes open.  Some of them sleep by keeping themselves balanced with small and slow movements in one place while others lie either on the bottom, in holes, in vegetation, or wherever they find protection.    

How Do Fish Sense and Communicate in the Ocean?

The fish’s conscious awareness of their surroundings is mainly perceived through their sight, hearing, smell, touch, and taste. But most of these senses function in special ways.

Take for example the supposed natural difficulty of many types of fish that don’t have good vision. What they lack in that particular sensory capability is actually more than balanced by their extraordinary senses of hearing and taste.

Common among many fish species is their very keen sense of taste. Aside from having taste organs in their mouth, they also have them on their heads and some parts of their body (with some having these all over most of their body). Fish such as these are more than capable of searching out food without much need of their sense of sight.

While fish generally communicate through sound transmission in water, there are a few that use visual communication. One perfect example of this is how a small cleaner fish is able to remove gill parasites from the mouth of a much larger fish species without being eaten, even if it is a predator. The much larger fish simply visually recognizes the distinct color and actions of the cleaner fish and welcomes it into its mouth to do its purpose.  

What Do Fish in the Ocean Eat?

Just like land animals, fish species also have various types of preferences when it comes to feeding. Some feed on algae and aquatic plant life. Some that stay near the surface feed on smaller fish, insects and smaller land animals.

Those in the Cartilaginous group, prey on other types of fish. Large carnivores like the shark feed on large land animals if given the opportunity. 

Of these fish predators, one of the goriest when it comes to feeding are the Parasitic Lampreys. They are known as the vampires of the deep. They suck the blood, fluids, and tissues out of their prey by cutting through its sides with the many sharp, tiny teeth in their suction-cup-like mouth.

Non-parasitic Lampreys on the other hand are not as gory. They are typically filter feeding in freshwater.

How Do Fish in the Ocean Multiply?

Though fish breed and reproduce in various ways, there is commonality in the way they lay their eggs. Mostly, they lay a large number of small, fertilized eggs that they spread around them.

Some species that live in the pelagic zone simply suspend their eggs in open water. There are others still, especially freshwater species, that place their eggs either on the bottom or hidden among aquatic plants.

There are many problems that these eggs face, other fish preying on them being one. This is why, of the numerous eggs laid (hundreds, thousands, or millions, depending on the species) only a few will remain and live to grow.

Interesting Facts About Fish in the Ocean

  • The Oceanic Flying Fish can glide hundreds of yards on the surface of the water.
  • The South American Freshwater Flying Fish can jump a few feet above water with a speed of 10 mph and do a single glide of more than a hundred meters.
  • The Sailfish can swim up to 68 mph, making it the fastest fish.
  • The male Angler P. Spiniceps measures only 6.2-7mm long, making it the smallest male fish.
  • The Whale Shark can weigh up to 20 tons and measures around 40 feet, making it both the heaviest and the longest fish.
  • The Bathylychnops Exilis has four eyes, making it the fish with the most eyes. 
  • The Dwarf Lanternshark measures only 6.2 inches, making it the smallest shark. 
  • The Puffer Fish contains tetrodotoxin, which is several times more lethal than cyanide, making it the most poisonous fish.
  • The Stone Fish’s spines contain venom that can be fatal if not properly treated, making it the most venomous fish.

Final Thoughts

Even with advancements in technology, scientists and experts are still unable to keep an accurate and updated count of how many fish live in the ocean today. Organizations like the Census of Marine Life, however, are able to document and update the database on how many species of marine life are present in the ocean. And that’s another topic altogether.

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Growing up on the south shore of Long Island, Chum Charlie has always had a passion for fishing. His favorite fish to catch is a striped bass and his favorite bait to use is bunker. Off the water, he enjoys blogging and sharing his favorite fishing tips & tricks that he has learned over the years.