do catfish have backbones

Do Catfish Have Backbones? (or Spineless)

There are over 3,000 species of catfish. In fact, one in ten species of fish is a catfish, and one in every twenty vertebrates is a catfish. Scientists use characteristics like skeletal structure, bones, cartilage and scales to classify catfish and other species of animals.

So, do catfish have backbones? Catfish are vertebrates because they have a backbone. The backbone runs the length of the body from the head to the tail and provides a central support structure. It protects the rest of the catfish’s body, including the vital organs and muscles.

All species of fish have a backbone (except for the hagfish, which is a notable exception.) Having a backbone, or spine, classifies fish as vertebrates. While catfish share many characteristics with the majority of other fish, they also have many unique qualities.

Vertebrate vs. Invertebrate

Animals are classified as either vertebrate or invertebrate. If an animal species has a backbone, it is classified as a vertebrate, just like the catfish. Vertebrates only make up 2% of all animal species, however. The other 98% are invertebrates, meaning they do not have a backbone.

A backbone is also known as a spine. The segmented bones that make up a backbone are called vertebrae. The rest of the body is built around and supported by the backbone.

Both vertebrates and invertebrates have a flexible rod, called a notochord, which runs the length of their body during some stage of their development. In vertebrates, the notochord is replaced by the vertebrae as it develops.

The vertebrae not only support the spinal cord, they also fully surround it to protect it from injury. The spinal cord is the network of nerves that carries messages from all parts of the body to and from the brain. Therefore, having a backbone is of great benefit to an animal.

Benefits of a backbone

There are many differences between animals with backbones and animals without backbones because having a well-protected and supported spinal column allows animals to develop more fully.

Size is the most notable difference between vertebrates and invertebrates. Animals without a backbone cannot support large muscular or skeletal structures. This usually keeps them from getting very big. The giant squid is a rather large exception, however. Even without a backbone, it can grow to over 50 feet in length.

Generally speaking, though, species without backbones are much smaller.  The smallest invertebrates are single-celled organisms, such as amoebas. Many species of invertebrates, like insects, are quite small.

The nervous systems of vertebrates, including us humans, are more fully formed than invertebrates like earthworms, shrimps or ants. The support provided by a backbone allows the spinal cord and the rest of the nervous system to be well-developed.

Because of this, vertebrates can adapt to their environments more easily. They are able to use their nervous system to sense changes in their environment and they can make changes in their behavior or move to another location to protect themselves.

Animals that have backbones

There are about 60,000 different species of vertebrates.  Vertebrates are classified into one of these main categories:

  1. fish
  2. amphibians
  3. reptiles
  4. birds
  5. mammals

Animals that don’t have backbones

Remember that 98% of animals don’t have a backbone. Approximately 1.25 million species of invertebrates have been classified and described by scientists. These include:

  1. protozoans, such as amoebas and paramecia
  2. annelids, such as worms and leeches
  3. echinoderms, such as sea cucumbers and starfish
  4. mollusks, such as clams and snails
  5. arthropods, such as insects and shrimp

Because it has a backbone, catfish can grow to be quite large. There is a wide variety in the sizes of catfish, however. They range from as small one inch to as large as over 5 feet. Because they have a backbone and a centralized nervous system, they can respond to stimulus in their environment.

Bone vs. Cartilage

Some people wonder if catfish have bones or cartilage, like a shark. Like the majority of fish species, catfish are bony fish.

There are five main different types of fish, but two of them have gone extinct. Of the three remaining types, there are bony fish, cartilaginous fish and jawless fish.

  1. Bony fish have skeletons made of bone rather than cartilage. Bony fish have a swim bladder that fills with oxygen and other gases from their bloodstream and allows them to float. 
  2. Fish like sharks and rays are cartilaginous fish. They store a lot of oil in their liver in order to stay afloat, but they are heavier and must continually stay swimming so that they stay afloat.
  3. Jawless fish are the other type of fish that exist. They have lived for over 500 million years and there are only 60 species. The hagfish and lamprey eel are in this group.

What is the difference between bone and cartilage?

Bone and cartilage have similar functions but there are many differences. Below is a summary of some of their major characteristics.

BoneCartilage
Inflexible and toughFlexible and elastic
Cells are called osteocytesCells are called chondrocytes
Has blood vesselsDoes not have blood vessels
Both organic and inorganicEntirely organic
Always has calcium saltsMay or may not have calcium salts
Grows in two directionsGrows in one direction
Bone marrow is presentNo bone marrow
Two types: compact and spongyThree types: elastic, hyaline and fibro

Fresh water vs. Salt Water

Fish with cartilaginous skeletons, like sharks, can only live in saltwater. However, bony fish, like catfish, can live in all types of water.

There are 37 families of catfish and they can be found all over the world in all different types of water. Catfish can live in fresh water or saltwater, and even brackish water.

While many people are familiar with freshwater catfish, there are also many species of saltwater catfish. They are found prevalently in the Atlantic Ocean, from Texas to Virginia.

The Florida saltwater catfish is a type of catfish that has a venomous sting. If you are stung by one of these catfish, it can easily become infected. There are varieties of freshwater catfish that are also venomous.

Scales vs. No Scales

Another major difference between catfish and other types of fish is the fact that catfish do not have scales. The question of scales or no scales adds to the confusion when it comes to classifying and describing fish.

Many people think that all fish have scales, but there are several fish that do not. These fish are in the catfish, clingfish and shark families. Despite the many benefits of scales, these fish have evolved without them.

Benefits of scales

Scales grow out of the skin of fish and vary in size and shape. Some fish have large, beautiful, iridescent scales, while other fish appear to have no scales because their scales are so tiny.

Scales help protect fish from injury and may also provide camouflage if they are colored or reflect light. Scales also protect fish from disease, particularly bacterial infections. Scales can even make it easier for fish to swim, as they are structured in a way that reduces resistance when they swim.

Types of scales

There are four main types of scales among fish.

  1. Placoid-These scales are also called dermal denticles, and they are barbed. Sharks have tiny placoid scales that are made out of the same materials as a human tooth. Their skin feels like sandpaper and is rough enough to cause abrasions on human skin.
  2. Cycloid-These scales are thin and translucent. They are also circular and have rings on them. These rings grow as the fish ages; the more rings, the older the fish. Cod and carp are examples of fish with cycloid scales.
  3. Ctenoid-These scales have a comb-like appearance. They are attached more firmly to the skin than cycloid scales. They can be found on sunfish and flounder.
  4. Ganoid-These scales are found on fish with cartilaginous skeletons, like sturgeon and gar fish. These types of scales, also called scutes, are bony plates that don’t overlap.

Fish without scales

Fish that don’t have scales have other ways to protect their vulnerable insides. Some fish, like the catfish, evolved differently and do not need scales. They have different lifestyles and habitats that don’t require them to have scales.

Some, like the Conger eel, have extra thick layers of skin that excrete mucus and proteins to create a slime that protects it. The hagfish has muscle fibers embedded in its tough skin, which makes it useful as a type of leather for different garments.

Catfish bodies have mucus covered skin. Some of them have scutes, which are large bony plates (similar to fingernails, in how they are made and attached). Interestingly, there are even catfish species who breathe through their skin.

There are even some catfish species that can change colors, similar to a chameleon. In the wild, catfish change colors to protect themselves from predators. But even catfish in home aquariums will change colors when they are stressed.

Certain species of catfish, as previously mentioned, also have venomous barbs that provide protection. As you can see, there are many ways that a catfish can protect itself.

Conclusion: Do Catfish Have Backbones?

While catfish are vertebrates and thus have a backbone, they do have some other unique characteristics that set them apart from other fish.

The fact that they do not have scales makes them special and is an easy way to identify them. This makes them easier for scientists to classify and describe.