Are Octopuses Classified as Fish? Discover Crucial Differences

No, octopuses are not fish. They are mollusks, like clams and snails. In fact, octopuses are like super-intelligent, highly-evolved clams with eight arms rather than one foot!

Octopuses, along with squid, cuttlefish, and nautiluses, are members of the class Cephalopoda, which belongs to the phylum Mollusca. Cephalopods are highly advanced and organized marine animals without backbones or vertebrae, making them invertebrates.

So why aren’t octopuses considered fish? Well, fish typically have backbones, so they belong to the phylum Chordata. Fish are generally characterized by having vertebrae, gills, and fins. Octopuses, as mollusks, do not possess these features and differ significantly in their anatomy.

You’ve come to the right place to learn what makes octopuses different from fish.

BTW, for you biology nerds out there, Chordata refers to a phylum of animals that includes vertebrates, such as fish, amphibians, reptiles, birds, and mammals. Chordates are characterized by the presence of a notochord, a hollow nerve cord, pharyngeal gill slits, and a post-anal tail at some stage of their development.

Read George’s new book –

The Octopus Paradox: 9 Brains, 3 Hearts, and 8 Arms Make for a Fascinating Creature” Learn how octopuses make nine brains work as one!

Dive into the mesmerizing world of octopuses with this captivating book! Explore their incredible abilities, from problem-solving to tool usage. Discover the intriguing behaviors that hint at their possible consciousness. Immerse yourself in a journey that unveils the mysteries of these fascinating creatures. Get ready to be amazed and gain a whole new appreciation for the extraordinary octopus.

Book cover for Octopus Paradox by George Sranko

Classification of Octopuses

Octopuses are fascinating creatures that can often be misunderstood. You might wonder if they are classified as fish or something else. In this section, we will clarify the classification of octopuses.

Octopuses are part of the phylum Mollusca, which includes various invertebrates such as snails, clams, and squid. Within this diverse group, octopuses are members of the class Cephalopoda.

Cephalopods are a unique group of marine animals that possess a highly developed nervous system, complex behavior, and remarkable agility. Some familiar cephalopods include not only octopuses, but also squid, cuttlefish, and the chambered nautilus.

Further diving into the classification, octopuses belong to the order Octopoda. This order is comprised of around 300 known species of octopuses. There are two main suborders within Octopoda: Cirrina and Incirrina. Cirrate octopuses have fins on their mantle and a small internal shell, while Incirrate octopuses lack these features.

Now that you have a better understanding of the classification of octopuses, you can see that they are not fish. Instead, they occupy their own distinct category within the animal kingdom as intelligent and highly adaptable marine invertebrates.

Characteristics of Fish

Physical Features

When you think about fish and their physical features, you typically imagine a streamlined body, fins, scales, and gills. Fish have a skeleton that is either made of cartilage (sharks have cartilage) or bone, which supports their body structure and allows them to swim effectively. They primarily use their gills to breathe by extracting oxygen from water.

However, when you look at octopuses, you won’t find these traditional fish characteristics. Instead, they have a soft, rounded body with eight long arms lined with suckers, as well as a pair of bulging eyes. Furthermore, they don’t have a hard skeleton, so their body is very flexible, enabling them to fit into small spaces and move with ease.


Fish reproductive patterns can vary, but most fish either lay eggs or give birth to live young. When it comes to egg-laying, some fish provide parental care and protect the eggs, while others release the eggs into the water and leave them to fend for themselves.

On the other hand, octopuses have a unique reproduction process. The female octopus will lay thousands of eggs and carefully guard them in her den, constantly cleaning and aerating them. The male octopus plays no role in taking care of the eggs. In many species, the female dies shortly after the eggs hatch, marking the completion of her lifecycle.


Fish can be found in various aquatic environments, such as oceans, rivers, lakes, and even ponds. They adapt to their specific habitat, depending on factors like water temperature, salinity, depth, and available food sources.

Octopuses, meanwhile, primarily reside in coastal marine waters. They, too, can adapt to different habitats but spend most of their time in dens – small holes and crevices in rocks and coral. Octopuses are solitary creatures, and they are territorial, meaning they don’t typically share their dens with other octopuses.

Some octopuses inhabit the deep waters of the open ocean, and can be found at depths of over 1,000 meters (3,300 feet). They prefer areas with rocky or muddy substrates where they can find shelter.

As you can see, there are significant differences between fish and octopuses in terms of their physical features, reproduction, and habitat. While both are aquatic creatures, it’s important to understand that octopuses are not classified as fish.

Octopus Features


Octopuses have unique anatomical structures that set them apart from fish.

Their body mainly consists of a soft, flat shape known as the mantle. This is where their vital organs, such as the heart and gills, are located.

Octopuses have eight arms, hence their name, and these arms are lined with suckers that allow them to grasp, taste, and manipulate objects. Furthermore, they don’t have any bones, which makes them highly flexible.


Unlike fish, octopuses primarily move by crawling along the seafloor or using jet propulsion. They’re quite agile, and their boneless bodies can navigate complex environments.

They have a specialized structure called a siphon, which allows them to draw water into their mantle cavity and expel it forcefully. This jet propulsion method enables them to swim backward at high speeds. Additionally, they can also change their skin color and texture, which aids in camouflage and communication.


When it comes to intelligence, octopuses stand out compared to fish.

They have a remarkably developed nervous system, with a large brain relative to their body size. This allows them to exhibit complex behaviors, learning, and problem-solving abilities.

In fact, they have been known to navigate mazes, unscrew jars, and use tools to access food. Their learning capabilities, combined with their natural curiosity, make octopuses fascinating creatures to study compared to most fish species.

Cephalopod Characteristics

Octopuses have:

  • Eight arms covered in suction cups: While fish have fins for locomotion, octopuses rely on their flexible, muscular arms for movement and capturing prey.
  • A soft body: Unlike fish, which usually have bony skeletons, octopuses are primarily soft-bodied, apart from their hard beaks used to crush prey.
  • Three hearts: In contrast to fish, octopuses have multiple hearts that pump blood through their bodies.
  • Blue blood: Octopuses utilize copper-based hemocyanin, making their blood blue, instead of the iron-based hemoglobin found in fish.

When you compare an octopus to a fish, it becomes quite apparent how distinct their characteristics are. While both live in aquatic environments and have some similarities in their diets, octopuses’ unique traits set them apart.

Environmental Adaptations


You might be surprised to learn about the incredible environmental adaptations unique to octopuses!

These fascinating creatures can change their colors using special cells called chromatophores to blend in with their surroundings, making them masters of camouflage. They also have jet propulsion capabilities, using water pressure to quickly expel water through a tube called the siphon, giving them a speedy escape when needed.

Moreover, octopuses possess defensive ink sacs that release dark, ink-like substances to confuse predators. In addition to these adaptations, they can regrow lost limbs and have suction caps on their tentacles, allowing them to grip and manipulate objects with ease. It’s evident that octopuses have evolved brilliantly to survive in their underwater habitats.


Fish, on the other hand, display a wide range of environmental adaptations as well. One key adaptation is their streamlined body shape, which reduces water resistance and enables them to swim efficiently. Their scales also provide protection and help to prevent water loss.

Many fish species possess a swim bladder, an air-filled organ that helps them maintain buoyancy and navigate at different depths in the water. Additionally, gills are essential for extracting oxygen from water, allowing fish to breathe and survive underwater.

Some fish have developed specialized adaptations depending on their environment; for example, deep-sea fish may produce bioluminescent light to attract prey or communicate with one another in the dark depths of the ocean.

Comparing Fish and Octopuses

One of the key differences between fish and octopuses is their respiratory system. Fish use gills to extract oxygen from water, while octopuses have three hearts and use gills as well as their skin to breathe.

Another distinction lies in their sensory systems. Fish typically have a lateral line system that can detect changes in water pressure, vibrations, and currents, allowing them to perceive their surroundings. Octopuses, on the other hand, possess highly developed central nervous systems and are known for their remarkable problem-solving abilities and intelligence.

Fish have a wide variety of reproductive strategies, including laying eggs in nests, livebearing, and mouthbrooding. Octopuses, however, typically lay thousands of eggs in a safe location and the female guards them until they hatch, often without eating during this time.

In terms of diet, fish and octopuses share some similarities. Both can be carnivorous, and they rely on a range of aquatic animals for sustenance. For example, fish may eat smaller fish, crustaceans, and mollusks, while octopuses might consume crabs, clams, and other marine creatures.

Misconceptions About Classification

It’s a common misconception that octopuses are classified as fish due to their aquatic habitats and shared classification strata of the Animalia kingdom. However, this is not accurate. Let’s dive into the finer details of their classification to clear up any confusion.

Firstly, octopuses belong to the class Cephalopoda, which includes squids, cuttlefish, and nautiloids. This class falls under the phylum Mollusca, which comprises soft-bodied animals like slugs, snails, and clams. On the other hand, fish belong to the phylum Chordata and the subphylum Vertebrata, making them distinctly different from octopuses in terms of classification.

Mollusks are characterized by their soft bodies, lack of an internal skeleton, and the presence of various types of shells in some classes. The octopus, as a cephalopod, has a unique body structure consisting of eight-limbs, a soft body, and beak-like jaws differentiating them from fish, who possess fins and a backbone.

Another key factor distinguishing octopuses from fish is their behavior and reproductive strategies. Octopuses use their arms and specialized skin to camouflage, change color, and manipulate objects, while the behavior of fish mainly relies on their fins and swim bladders for stability and swimming. They also differ in how they reproduce: octopuses use internal fertilization, while most fish engage in external fertilization.

When considering these points, it becomes clear that octopuses are not classified as fish. However, they do share similarities: both are marine animals and have unique adaptations to surviving in their respective environments.

Significance of Accurate Classification

When it comes to understanding the complex world of marine life, accurate classification is important. This ensures that you and other researchers can make sense of the differences and similarities between species. Let’s take a closer look at why classifying octopuses as fish could lead to confusion and why it’s important to be precise.

Firstly, octopuses and fish exhibit several distinct differences in their physical characteristics. Unlike fish, octopuses have soft bodies and eight sucker-bearing arms. This distinct morphology makes it important to separate octopuses from fish in order to accurately study and compare their biology and evolution.

Secondly, octopuses are members of the class Cephalopoda, a group of marine mollusks which also includes squid and cuttlefish. Fish, on the other hand, belong to different taxonomic groups—either Osteichthyes (bony fish) or Chondrichthyes (cartilaginous fish). By accurately classifying octopuses within the Cephalopoda group, you’ll have a clearer understanding of their relatedness and shared traits with other members of their class.

Another reason to be precise about octopuses’ classification is the difference in their behavioral and cognitive abilities. Octopuses are known to be highly intelligent creatures with advanced problem-solving skills. They possess impressive learning abilities, which has led researchers to regard them as the most intelligent among invertebrates. Fish, while varied in their cognitive capabilities, often do not exhibit the same level of intelligence as octopuses. Accurate classification helps in making connections and understanding these behavioral differences.

Additionally, when studying the diets and ecological roles of marine organisms, accurate classification becomes imperative. Octopuses primarily feed on crustaceans and other mollusks, whereas fish diets can vary greatly depending on the species. Understanding the ecological role of octopuses requires distinguishing them from fish in food webs and ecosystem analyses.

Frequently Asked Questions

What is the scientific classification of octopuses?

Octopuses belong to the class Cephalopoda and have the scientific name Octopoda. They are marine animals known for their unique physical features and incredible intelligence.

Do octopuses lay eggs?

Yes, octopuses do lay eggs. Female octopuses lay thousands of eggs and usually protect them until they hatch. During this time, they might not eat, eventually leading to the mother’s death after the eggs hatch.

Are octopuses invertebrates?

Indeed, octopuses are invertebrates. This means that they do not have a backbone or spinal column. They have a soft body structure, which allows them to move and squeeze into tight spaces.

Do octopuses belong to the mollusk family?

Yes, octopuses are part of the mollusk family. They are more closely related to snails and clams than they are to fish. Mollusks are a diverse group of animals that have a soft body and typically lack a backbone.

What do octopuses eat?

Octopuses are carnivorous animals. Their diet primarily consists of crustaceans, such as crabs and shrimp, as well as fish and even other smaller octopuses. They use their agile arms and powerful beak-like mouth to catch and dismantle their prey.