Species Of Fish

Fish, which are cold-blooded aquatic vertebrates with scales, were the first animals to produce bones. Anaspis, the first fossil, is estimated to have been armored and jawless and dates back more than 500 million years. Fish may have multiplied in the ocean due to subsequent jaw creation 400 million years ago or so.

How many species of fish are there in the ocean? The latest count of existing and extinct fish species in the oceans is 33,600. These fishes have different shapes, sizes, and colors, and they live in a spectrum of depths and temperatures.

The ocean is home to different kinds of aquatic animals, including thousands of fish species. There are three types of fish species, which I will discuss as we go along in this article.

Fish In The Ocean

Fish are aquatic animals from the Chordata phylum group. They have gills, scales, and fins, which distinguish them from other creatures. Fish, as cold-blooded animals, must swim in the water of the appropriate temperature to regulate their body temperature.

The great group of animals living in seas, oceans, lakes, and rivers is the fish. Unlike amphibians, fish must spend their entire lives in the water. Even though fish can breathe air, they prefer breathing through their gills and obtaining oxygen from the water.

Fish live in bodies of water ranging from tiny ponds to the deepest portions of the ocean. They have an estimated total of about 33,600 species. According to some estimates, there are more fish species on the globe than any other vertebrate group.

Fish that are cartilaginous in nature are the largest. Whale sharks, basking sharks, and other sharks are among these massive swimming creatures. The beluga (sturgeon) is among the largest bony fish species found in the oceans. The tiniest fish can be as little as a few millimeters in length.

It’s vital to remember that just because an animal lives in water doesn’t guarantee it’s a member of the fish world. Whales, for example, belong to the Mammalia class since they nourish their young with milk. They have lungs, unlike fish, and must come to the surface of the water to breathe.

Fish that belong to the bony family are the most commonly consumed. Salmon, pollock, cod, mackerel, and tuna are examples of these fish.

Bony Fish

Sutures in the neurocranium and segmented fin rays originating from the epidermis in all bony fishes. Gills are present in both fishes (bony and cartilaginous), but bony fish have a hard, bony plate covering their gills.

An “operculum” is the name for this feature. Fins of bony fish may also have distinct rays or spines.

Bony fish, unlike cartilaginous fish, have swim or gas bladders that help them maintain their buoyancy. Cartilaginous fish, on the other hand, are continually swimming to stay afloat.


Bony fish is a member of the Osteichthyes class, which separates into two categories:

  • Lobe-finned fishes (Sarcopterygii). It includes the coelacanths and lungfishes.
  • Ray-finned fishes, or Actinopterygii

There are around 25,000 species in the subclass Sarcopterygii, all of which have enamel on their teeth. Their upper jaws connect with their skulls featuring a central axis of bone that works as a unique skeletal support for fins and limbs.

The Sarcopterygii includes two important taxa of fish:

  1. The Ceratodontiformes (lungfishes)
  2. The Coelacanthiformes (coelacanths)

There are 33,000 species in Actinopterygii, divided into 453 families. They live in many types of aquatic environments and can grow to be over 26 feet long. However, 5,000 pounds is the maximum weight for the Ocean sunfish.

The pectoral fins of this subclass are large, and the pelvic fins are united.

  • Chondrostei are primordial ray-finned bony fishes
  • Holostei or Neopterygii are intermediate ray-finned fishes such as sturgeons, paddlefish, and bichirs.
  • Teleostei or Neopterygii are advanced bony fishes like herring, salmon, and perch.


Bony fishes have a wide range of feeding preferences as a group. Some are herbivores, others are carnivores, while others are omnivores.

Bony fishes may eat a wide range of plants and animals. They can eat anything from the tiniest plant plankton to the largest marine animals as a group.

They eat annelid worms, sea snails, mussels, clams, squids, crabs, insects, birds, amphibians, small mammals, and other fishes.


Bony fish exist in practically any body of water. Tropical, temperate, polar oceans, all freshwater ecosystems are all home to them.

Some bony fish species can live as far down as 11 kilometers (6.8 miles) in the deep water. Other species live in lakes that are up to 5 kilometers (3.1 miles) above sea level.

More than 13,000 species of bony fish exist in marine habitats. It accounts for about 58 percent of all bony fish species.

Popular Examples Of Bony Fish

  • Porkfish
  • Atlantic Porkfish
  • Spadefish
  • Atlantic Spadefish
  • Balloonfish
  • Balloonfish
  • Barracuda
  • Barracudas
  • Blue Tang
  • Blue Tang
  • Blue striped Grunt
  • Blue striped Grunt
  • Cichlids
  • Cichlids
  • Image coming soon.
  • Crevalle Jack
  • French Angelfish
  • French Angelfish
  • French Grunt
  • French Grunt
  • Gars
  • Gars
  • Gray Angelfish
  • Gray Angelfish
  • Great Barracuda
  • Great Barracuda
  • Grouper
  • Groupers
  • Leafy Sea Dragon
  • Leafy Sea Dragon
  • Lionfish
  • Lionfish – Scorpionfish – Stonefish
  • Lookdown
  • Lookdown
  • Moray Eel
  • Morays
  • Parrotfish
  • Parrotfish
  • Piranha
  • Piranhas
  • Pufferfish
  • Pufferfish & Porcupinefish
  • Queen Angelfish
  • Queen Angelfish
  • Parrotfish
  • Queen Parrotfish
  • Scrawled Filefish
  • Scrawled Filefish
  • Sea Horse
  • Seahorses
  • Wild Sergeant Major
  • Sergeant Major
  • Tuna


Freshwater, seawater, and brackish (a mix of freshwater and saltwater) habitats are all home to bony fish. The salinity of seawater is around 35 parts per million (parts per thousand).

Some species are tolerant of greater salinity levels. Some goby species may withstand salt levels of up to 60 parts per million.

Fish live in almost every type of aquatic environment. Fish have evolved to live in a variety of locations, such as:

  1. Rocky coastlines
  2. Coral reefs
  3. Kelp forests
  4. Rivers and streams
  5. Lakes and ponds
  6. Undersea ice
  7. Deep-sea, and other fresh, salt, and brackish water settings

Pelagic fish live in the open ocean. Tunas, for example, is one in many species in the family Scombridae, subfamily Thunninae.

Flatfishes (order Pleuronectiformes), for example, have evolved to live on the seafloor. Gobies, for example, burrow into the substrate or bury themselves in the sand.

During a summer drought, some lungfish “hibernate.” They love to bury themselves in the mud of a dried-up pond. In the darkness of caverns, some fish species dwell in freshwater ecosystems.

Bony fishes can live at a variety of temperatures, depending on the species. Some people live in frigid climates.

Desert pupfish (Cyprinodon macularius) live in hot springs in California that reach temperatures of around 45°C (113°F).

Some bony fish species can withstand the cold temperatures of the Arctic and Antarctic. The blood of these uniquely adapted fishes contains glycoprotein molecules that lower the freezing point of the blood. Boreogadus saida, the arctic cod, can withstand temperatures as low as -2°C (28°F).

Fishes, in general, rely on oxygen dissolved in water to breathe.

Some bony fish species require a lot of dissolved oxygen to survive. Brown trout (Salmo trutta) need up to 11 milligrams of dissolved oxygen per liter to survive.

Misgurnus fossilis, a kind of loach, can live in water with as little as 0.5 mg of oxygen per liter (0.5 ppm).

Mudskippers (family Periophthalmidae) have gill chambers that can hold a tiny amount of water. They spend the most time on land. They only return to mud holes when their water supply runs out.

African lungfishes (subclass Dipnoi) breathe by sucking air into a “lung.” These fish, in reality, must have access to the water’s surface to survive.

Evolutionary History

Over 500 million years ago, the first fish-like organisms arose. About 420 million years ago, bony fish and cartilaginous fish split into two classes.

Cartilaginous creatures have a reputation for being more primitive for some reason. The evolution of bony fish led to the emergence of bony skeletons in land-dwelling vertebrates.

And the gill structure was a trait that would later evolve into air-breathing lungs. As a result, bony fishes are a more direct ancestor of humans.

Cartilaginous Fish

Cartilaginous fish (scientific name Chondrichthyes) have a cartilage-based skeleton rather than a bone-based skeleton. Cartilage is robust and flexible, providing enough structural support for these fish to develop to enormous proportions.

Sharks, rays, skates, and chimeras are examples of cartilaginous fish. There are approximately more than 600 different species of rays and skates and 500 different shark species.

Rays and skates live in waters all over the world. The majority of rays and skates live below the ocean’s bottom, but others live in open water. Freshwater rays exist as well.

The manta ray (Manta birostris) is the largest, reaching over 9 meters in length and weighing many tons. It feeds on plankton and tiny fish.

The common skate (Dipturus batis) is the world’s gigantic skate, growing up to 2.5 meters in length and living for roughly 50 years.

A short-nose electric ray, which is about 10 cm across and weighs around 0.5 kg, is the tiniest. The starry skate (Raja stellata) is the smallest, reaching a maximum total length of only 76 cm.

Skates and rays have their mouths, noses, and gill slits on the bottom of their bodies. Their spiracles and eyes are on the upper side. On the upper surface and tail of several species, there are spines and thorns.

Mature males, like sharks, can be distinguished by a pair of claspers beneath the pelvic fins. Females do not have them.


The 1,000 or so species of cartilaginous fish separates into two groups:

  1.  Sharks, rays, and skates
  2. Chimera or ghost sharks

The dwarf lantern shark, at 6.3 inches long, is the smallest of the group. The whale shark, at nearly 50 feet long, is the largest.

Jaws are apparent in sharks and other cartilaginous fish. These fish descended from jawless fish millions of years ago. So, why did fish develop jaws in the first place?

Fish would be able to eat a considerably more variety of foods, including plants and other species. Hence, the adaptation.

The following are some more characteristics of cartilaginous fish:

  • Paired fins.
  • Paired nostrils.
  • Scales.
  • Two-chambered hearts.
  • Rather than being composed of bone, the cartilage is skeletons. Cartilage is a supporting tissue that lacks the same amount of calcium as bones, causing bones to become inflexible. Cartilage is a softer, more malleable material than bone.


The nutrition of cartilaginous fish differs by species. Sharks are powerful apex predators that eat fish as well as marine mammals like seals and whales.

Rays and skates, which mostly live on the ocean floor, devour other bottom-dwelling species. Whale sharks, basking sharks, and manta rays, for example, are big cartilaginous fish that feed on microscopic plankton.


Sharks and rays are primarily marine fish. However, many enter estuaries, some go up rivers, and a few are permanent freshwater dwellers.

The majority of species live in the relatively shallow seas of continental margins or around offshore islands. Only a few roaming far out into the oceans.

Others are surface swimmers or live on the bottom in shallow waters. Some reside at vast depths, in midwives, or on the bottom.

Sharks and rays were considered trash before but are now becoming more common in most countries’ fisheries. The numbers of more valuable bony fishes are dwindling fast. As a result, many fisheries focus on elasmobranchs as a commercial resource.

The production of the annual yields goes up to 750,000 metric tons (approximately 827,000 short tons). Most of which are sold as fresh, dried, salted, or processed.

Many sharks and ray populations are depleting. Several species experience destruction as a result of this intense harvest. One effect of the extinction of these top-level predators could be a disruption of the marine food chain.

Popular Examples Of Cartilaginous Fish

  • Whale Shark
  • Basking Shark
  • Great White Shark
  • Thresher Sharks
  • Skates
  • Southern Stingray


Cartilaginous fish live all over the world. These fishes have lived in many sorts of environments, ranging from shallow, sandy bottoms to deep, open ocean sharks.


The earliest sharks originated about 400 million years ago, according to fossil data. Fossil data came from shark teeth, which are considerably more easily preserved than any other element of a shark.

Around 35 million years ago,’ modern’ sharks appeared, and megalodon, white sharks, and hammerhead sharks appeared 23 million years ago.

Rays and skates have been alive for longer than humans have. However, their fossil evidence dates roughly 150 million years and evolved after the first sharks.


  • Doliodus-like spiny shark forebears gave rise to the first Cartilaginous fishes.
  • The Holocephali and Elasmobranchii separated in the Silurian (421 million years ago).
  • The rays/skates and sharks separated in the Carboniferous 306 million years ago.

Jawless Fish

What is the definition of a fish with no jaws? You’ve probably guessed it. A jawless fish is what it sounds like, a fish without a jaw. Other characteristics, however, are shared by this group of organisms.

Why would a creature like this evolve? These fish were the very first vertebrates to appear on the scene. However, it does make sense logically.

Early jawless fish are assumed to have relied on filter-feeding to catch their prey. These fishes would have sucked water and debris from the seafloor into their mouths before discharging water and waste.

These jawless fish developed to feed on other fish species as some sea life evolved. They are now a problem in their habitat, according to some studies. There are no natural predators for lampreys.


The jawless fish, according to most experts, belong to the superclass Agnatha. They are members of the Chordata phylum and the Vertebrata subphylum. Jawless fish separates into two groups, each with roughly 100 species:

1. Lampreys

Although the lamprey resembles an eel, it possesses a jawless sucking mouth to adhere to a fish, a parasite that feeds on the tissue and fluids of the fish to which it is attached. A ring of cartilage supports the lamprey’s mouth. It features rows of horny teeth that it uses to latch on to a fish.

Lampreys can grow up to 40 inches long and can live in temperate rivers and coastal oceans. Lampreys begin their existence as larvae in freshwater. Lamprey usually lives as larvae on muddy river bottoms, where they filter feed on microorganisms.

The larval stage can persist for up to seven years! The lamprey transforms into an eel-like creature. They swim and usually attach themselves to a fish after its larval stage. Lampreys live in roughly 50 different species.

2. Hagfish

The slime fish is another name for the hagfish. It has an eel-like appearance and is pinkish in hue. It has glands on its flanks that secrete a viscous, sticky slime that it employs to defend itself.

The hagfish can twist its body into knots! It could be to get rid of slime or to get away from predators. The hagfish may also sneeze to clean some slimy things from its nostrils.

Although the hagfish is nearly blind, it possesses a good sense of touch and smell. It has a ring of tentacles that it uses to feel for food around its mouth. Its jawless mouth has a tongue-like protrusion coming out of it. When the “tongue” is dragged back into the hagfish’s mouth, tooth-like rasps appear at the end of the projection.

Hagfish eat marine worms and other invertebrates. Its metabolism is slow, and it can go for up to seven months without eating. Hagfish that have just been born are smaller versions of adult hagfish.

The hagfish live in both the Northern and Southern Hemispheres, in chilly ocean waters. It can be found on muddy seabeds and can live in big groups of up to 15,000 people. Hagfish exist in roughly 60 different species.


These fish can live in muddy bottoms, intermediate depths, and cold water around the tunnels they dig. Only about 20 hagfish species are known to exist in the globe, according to scientists.

Lampreys are primarily freshwater fish that live in temperate climates but survive in saltwater. Between the tropics and the poles are the temperate zones.


Jawless fishes have evolved from the Cephalochordata (Amphioxus and its relatives). These are tiny and soft-bodied filter-feeding organisms similar to and maybe ancestral to modern sand-dwelling filter feeders. A notochord likely stiffened the body of the primordial mammals.

The earliest jawless fish with a bone discovered dates back 470 million years (Arandaspis). It resembles the oldest intact Sacabambaspis fossil from the Late Ordovician. The first Ordovician fish appear to be relatives (and possibly ancestors) of the later heterostracans.

Are Fish Species In The Ocean Decreasing?

Fish populations are dropping as oceans warm. This whole global warming thing is putting a crucial source of food and income at risk for millions of people.

The amount of seafood that people gather from a wide range of species decreased by 4.1 percent. This percentage, in particular, is a victim of human-caused climate change, according to studies.

In the following decades, global warming will put a strain on global food supplies. However, the latest findings indicate that climate change is already having a significant influence on seafood.

It distinguishes the effects of warming oceans from other variables such as overfishing.

Overfishing is the second reason for the decreasing fish population. Overfishing occurs when marine animals are caught quicker than they can reproduce.

From 10% in 1974 to 32% in 2008, the global proportion of overfished fisheries has steadily increased. Large quantities of wild fish, shrimp, snails, clams, scallops, squids, sea urchins, corals, seaweeds, turtles, whales, and other creatures in “fisheries.”

There are different types of overfishing, and there are many factors influencing species sensitivity to overfishing.

Illegal captures and trading exacerbate the problem of systemic overfishing. Illegal fishing is responsible for some of the worst ocean consequences. It accounts for up to 30% of catch or more for high-value species.

$34.6 billion is the reported illegal, unreported, and unregulated fishing nets criminals cost annually. However, these catches migrate through opaque supply chains. It is due to the lack of methods to track fish from catch to consumer and import limitations.


While there are thousands of unknown fish species in the deep ocean, the number of known fish is dwindling. Some of them are depleting in number, especially fish used in the food industry. Although 33,600 fish species may appear to be a large number, over half of them are endangered.