Are Lobsters Fish? (Explained)

Lobsters and fish may both live underwater, but does that make them the same animals? If you’ve ever wondered if lobsters are fish, in this blog post, we’ll talk all about them, their differences, and their similarities. Let’s begin with a quick answer:

Lobsters are not fish but crustaceans. There are many significant differences between them, such as how their body is built, their behavior, and habitat. They also belong to different phyla: fish belong to the phylum Chordata, and lobsters to the phylum Arthropod.

However, this certainly doesn’t tell the whole story. Below I’ll explain the main differences and similarities between lobsters and bugs. Furthermore, I’ll explain more about what animal lobsters are. Read on!

The differences between lobsters and fish

There are many differences between lobsters and fish, as they don’t even belong to the same phylum. Interestingly, lobsters are more related to insects that live on land than to fish. Below you can read about the biggest differences between lobsters and fish.

Invertebrates vs. vertebrates

One of the most significant differences between fish and lobsters is that fish are vertebrates, and lobsters are invertebrates. Vertebrates are animals that possess a backbone, and this includes all mammals, birds, reptiles, amphibians, and fish.

Lobsters are marine invertebrates, meaning they don’t have a backbone. They don’t have an inner skeleton or bones, but they carry an exoskeleton (shell). Other marine invertebrate examples are crabs, sponges, sea stars, marine worms, and many many more.

Classification

Despite the main two groups, invertebrates and vertebrates, animals are divided into smaller groups like phylum, subphylum, classes, orders, families, and thousands of genus and species. You might already know that lobsters and fish don’t even belong to the same phylum because fish are vertebrates, and lobsters are invertebrates.

Fish belong to the phylum Chordata, together with alligators, salamanders, birds, mammals, and more. Lobsters belong to the Arthropod phylum, together with other crustaceans, insects, mollusks, and more.

Teeth

Another difference is that all fish have teeth in their mouths (at least most of the species). Lobsters, on the other hand, don’t have teeth in their mouths but only in their stomachs. Their teeth are part of the structure called the gastric mill, which is used for grinding food inside the stomach.

Because of this, the way these animals eat significantly differs. Fish use their sharp teeth to capture and hold prey, and next, they swallow it in large pieces. In contrast, lobsters capture the prey with their claws or the first pairs of their legs. Next, they use mandibles to crush the food and pass it to their mouths.

The way they swim

Lobsters and fish move around in a completely different way. Fish move forward by using their fins and a tail. They contract the muscles from side to side and front to back. Their bodies push against the water and move animals forward.

Lobsters, most of the time, move around the seafloor by walking on their legs. They can move forward, backward, and to the sides. They can also swim when feeling threatened, and their most effective way is to swim backward.

In order to do that, they rapidly flex and extend their tail. Interestingly, while speed is most important during this escape swim, lobsters can also steer their body by rotating their tail. Thanks to this, they have the availability to change swimming directions.

Body parts

Lobsters and fish have their bodies built very differently. For instance, fish body is well adapted to swimming forward and has a streamlined body plan. It consists of the head, trunk, tail, and fins. Fish are long and narrow, which reduces water resistance when they swim.

Lobsters’ bodies consist of two parts: a cephalothorax and an abdomen. The cephalothorax is a fusion of the head and the thorax. It contains the antennae, eyes, mouthparts, and legs. The abdomen is a flexible tail that allows them to swim rapidly to escape predators.

They also have five pairs of legs which are modified depending on the species. For instance, clawed lobsters have the first pair of legs modified into large claws. Spiny lobsters don’t have claws but long antennae that protect them from predators.

Water salinity

Another difference between lobsters and fish is the water salinity adaptation. You’ve probably encountered fish in both freshwaters (rivers or lakes), and saltwaters (oceans or seas). This is because about 51% of fish are freshwater species, and 49% are saltwater species.

Depending on the species, fish adapted to almost all water salinities and can tolerate large changes in salinity. However, it doesn’t mean freshwater species can live in saltwater and vice versa. They would die because of the osmosis process.

Lobsters are exclusively saltwater animals, and none of the lobster species can survive in freshwater. Just like saltwater fish species, their cells wouldn’t survive it, and they’d eventually die.

The reason for this is the state of isotonic stability with the surrounding saltwater. This means that the same amount of water moves between the body tissues and salt water, and they cannot prevent the accumulation of fluids in their cells in low-salinity environments.

The similarities between lobsters and fish

Even though lobsters and fish belong to completely different families, they are a few similarities we can point out, such as the way they breathe or their diet.

Gills

Fish breathe oxygen from the water through their gills. The process of breathing begins when a fish gulps water through its mouth. Next, they pass it through the gills that are located just behind their head on each side.

Lobsters also breathe through their gills, which are located in a gill chamber. However, the process of breathing looks a bit different. Instead of taking the water in through the mouth, lobsters take the water in through the opening between their legs. Next, they absorb the oxygen from the water.

You can read more about how lobsters breathe in my other blog post: “Do Lobsters Have Gills?”.

Diet

The diet of lobsters and fish can be similar, but it can also be very different because of the fish species diversity. When we consider smaller saltwater fish species, their diet includes plants, shrimp, worms, crustaceans, sea urchins, and other fish.

Lobsters’ diet is very similar as they feed on fish, crustaceans (crabs, clams, mussels), sea urchins, worms, and some plants. Sometimes, they also eat other lobsters.

Regeneration of lost limbs

Unlike humans, fish and lobsters can regenerate their lost limbs. Many fish species can regenerate their tail or fins. Lobsters, however, can regrow their claws, walking legs, and antennae. They do this during the process called molting, which is the process of shedding their shells to grow.

After the first molt, their appendages are already back but smaller than the original. They will continue growing for a few months or years until reaching their normal size.

Defense mechanisms

The defense mechanism of lobsters and fish can sometimes be similar, depending on the species. For instance, spiny lobsters, as the name suggests, are covered in spines. They’re strong and forward-curving, so together with the hardshell, they can be very protective.

Some fish species also developed spines to protect themselves. Examples of species are lionfish and stonefish. In addition to painful and sharp spines, they also inject venom that can even be deadly to their predators.

What about “shellfish”?

Maybe you wonder why lobsters are considered as shellfish and why the name is so similar to the fish term. Well, even though the name suggests that, shellfish are not fish. Shellfish is a term used in the food industry, and it defines a group of aquatic invertebrates, such as mollusks, crustaceans, or echinoderms.

What animals are lobsters?

After we established that lobsters aren’t fish, let me explain what animals lobsters actually are.

Lobsters are marine crustaceans which are a large, diverse group of arthropods. This group consists of about 30,000 species, such as shrimp, krill, crabs, barnacles, crayfish, fish lice, and more. They are four major families of lobsters:

• the clawed lobster (Nephropidae),
• the spiny lobster, also known as rock lobster (Palinuridae),
• the slipper lobster, also known as Spanish lobster (Scyllaridea),
• the furry, also known as coral lobster (Synaxidae).

Lobsters’ families differ in how their body is built, their habitat, and their behavior. Despite the difference between the first pair of legs – claws, they have a lot of other distinct features. There are differences in the morphological structures on the front of their shell (carapace), the structure of their appendages, the shape of the carapace, the length and shape of their antennae, and more.

All lobsters have paired appendages: first antennae, second antennae, mandibles, first maxillae, and second maxillae. Next, they have five pairs of walking legs (pereiopods). These legs are slightly modified, depending on the lobster’s family. For example, in clawed lobster species, the first pair of legs is modified into large claws.

These invertebrates inhabit the bottom of every ocean, and the water temperature they live differs depending on the species. In general, clawed lobsters prefer colder waters and are very common in the Atlantic Ocean, especially along the North Atlantic coast of North America.

The non-clawed species, such as spiny lobsters, prefer tropical waters. You can often encounter them in tropical and subtropical parts of the Atlantic Ocean, the Caribbean Sea, and the Gulf of Mexico. They’re also found in the Mediterranean Sea, coastal waters of Southeast Asia, Australia, and South Africa.

Lobsters are incredibly interesting animals with fascinating life cycle and communication methods. They’re known to communicate by peeing at each other and sending chemicals that translate the smell into a message.

They can live more than 100 years and never stop growing. Lobsters are omnivorous, which means they eat both plants and animal matter. They mostly prey on fish, crabs,