Can fish swim backwards? What about upside down?

We all know that fish swim forward and can do so well. But what about in other directions? Well, let’s find out!

Can fish swim backward? What about upside down?

Fish can indeed swim backward as well as upside down. However, there are certain restrictions that apply. Not all fish can swim backwards, and very few can do it well. Similarly, while theoretically, all fish can swim upside down, we have yet to observe a large number of species doing so. In either case, these swimming techniques are rare, and fish will almost always swim forward.

So what causes the fish to exhibit this behavior of swimming backward or upside down at times? How do they manage to achieve it? Let’s find out!

How do fish swim?

To understand fish being able to swim backward or upside down, it is important that we understand how fish swim. The answer isn’t simple since it varies with species. Nonetheless, we have listed the most common styles in which fish are able to swim below.

Body/Caudal fin propulsion: This type of swimming involves moving the body along the water. In this method, fish move their bodies laterally, in the form of waves. Usually, these waves are larger near the rear of the fish. The waves then generate force, which allows the fish to move through the water. This type of swimming uses both the body of the fish as well as the tail fin.

Median/Paired fin propulsion: These types of fish use their fins to generate waves that allow for their bodies to move. The anal and dorsal fins of the body are used to achieve this. The fish that use this method of swimming use their anal or dorsal (or both) fins instead of their tails and body movements to move through the water.

Other methods: This group includes a range of other methods of moving in the water that is not covered by the methods stated above. These include walking, burrowing, flying, or the use of dynamic lift methods.

To further analyze if fish are able to swim backward depending on the type of swimming they use, we will explore the particularities of each of these categories of swimming.

Goldfish Swimming Upside Down (Video)

Body/Caudal fin propulsion

The body/caudal fin propulsion has a number of types of swimming in it. To understand it better, we need to first recognize if fish that use body/caudal fish propulsion will be able to swim backward at all.

These types of fish generate waves to enable movement. To be able to swim backward, these waves would essentially have to be reversed. This means that if a fish is able to move the front of their body as effectively as their rear ends, they can swim backward with ease.

Thus the fish that entirely use the body movement to allow for swimming can theoretically swim forward and backward with the same efficiency. Fish that use only their Caudal fins would be unable to achieve this form of movement.

To give a complete answer, it is important to look at the different categories of swimming within Body/Caudal fin propulsion.

Anguilliform: This type of swimming involves a very slight increase in the wave size as it moves across the body. Fish within this category can thus easily move backward. Eels use Anguilliform swimming techniques.

Sub-carangiform:  The waves formed by the front of the body are greatly reduced in this form, but are still significantly large. The fish can move backward, but not with the same efficiency as the Anguilliform. Trouts use this form of locomotion.

Carangiform: The front of the body does little in this form of movement, and the emphasis of the waves is typically around the rear end. Fish using this form of movement can still swim backward but would be significantly slower. Mackerel use this form of movement.

Thunniform: This form of movement has virtually all of the waves concentrated at the caudal fin. Tunas use this method of locomotion, and can not swim backward.

Median/Paired fin propulsion

This form of movement involves the fish having to use their fins to create waves and thus move. In order to be able to swim backward, the fish should thus be able to make their fins move in both directions.

While there are too many forms of locomotion that fall within this category to discuss, it is important to understand that most fish are easily able to move their paired anal and dorsal fins, or each individually, to move in any direction they wish to. This means that most fish that use this method would theoretically be able to move both ways.

That does not mean that they can move in both directions with equal efficiency though. While the fish that use these forms of movement typically have well-developed fins that can easily move in both directions to help them achieve their desired form of movement, fish simply don’t prefer moving backward!

However, there are some exceptions that we will be looking at later.

Other types of swimming

Fish tend to use a number of other types of swimming as well. These typically include one of the following few categories. It is important to remember that some fish may fall into multiple categories because they use a number of different ways to swim.

Dynamic lift: This form of movement disables all backward movement, and is debated to be the only form of swimming in which fish can not move backward at all. Fish are typically denser than water, and to maintain their depth, they tend to use gas bladders. Fish that lack both of these, maintain their depth by spreading out their fins. They thus have to constantly keep moving to stay afloat. They are also unable to use their fins to move their bodies backward. Sharks tend to use dynamic lift and are thus unable to move backward.

Walking: Fish that walk are typically found along the ocean floor. These can include a number of methods such as using their fins, moving at the ocean floor in a snake-like manner, or springing. These types of fish are able to move backward.

Flying: Fish that are able to fly have abnormally high “fins”. These fins can allow them to trap air and “fly” while they use their tail to propel forwards. They can typically swim backward, but tend to go only forward when they’re in their “flying” modes.

Are fish good at swimming backward?

Now we know that most types of fish are able to achieve some form of backward movement. This leads us to wonder if they can swim backward well. For most fish, we know that they can’t swim backward well.

This is obvious to us if we note that despite having the ability to move backward, fish tend to move forward and make “cuts” if they want to change direction. This is because fish are typically much greater at moving forward then backward.

Even fish that can move their body in both directions tend to prefer moving forward. This is simply because they aren’t used to moving in the other direction, much like humans. When their tails tend to oscillate more than their entire body, the efficiency of fish when moving backward is greatly reduced.

Both the hunted and the hunters tend to prefer faster movement. By using the tail to generate higher waves, fish are typically able to move much faster than they would have been when using anguilliform locomotion. This is one of the major factors that lead to them being bad at swimming backward.

So, in short, most fish are not great at moving backward because their method of locomotion does not allow for it. Swimming backward has little advantage for most fish, and they thus prefer to stick to swimming forwards.

Fish that can swim well backward

There are some fish that stand out when it comes to swimming backward. While most fish would be clumsy and slow in their attempts to move backward, certain types of fish have shown great efficiency in doing so.

The first form of fish is Anguilliformes. This includes eels. Eels are able to move backward with ease and can do so at great speeds.

The most notable example of fish that can move backward, however, comes in the form of the electric fish. Specifically, the knifefish tend to use backward motion a lot. This is because these fish tend to use electroreceptors to target their prey. By swimming backward, when their prey is scanned by their electroreceptors, it would be right in front of their mouths. This makes it easier for them to catch their meals. If they scanned while swimming forwards, the prey would have been at their tail by the time they had done so.

Not even the knifefish maintains this form of movement for long though. Fish can not move backward for a long time without suffocating. This is because of the way the gills of fish work. The gills require water to move in the correct direction in order to enable a fish to obtain oxygen. When fish swim backward, the water does not reach the gills in the right direction, causing a fish to suffocate and tire out.

Can fish swim upside down?

So now that we have seen that fish can swim backward, you must be wondering if they can do so upside down. The idea of a fish swimming upside down might seem very unusual and remote, but the fact is that this form of swimming is actually not unusual at all.

In fact, fish should be able to swim upside down just as well as they could swim the right side up. This is very interesting, since this means that the idea of fish swimming upside down is not that remote at all, and very possible.

Theoretically, fish are not really more streamlined in one direction than the other, and should thus have no preference between swimming upside down or the “normal” way. Similarly, fish are not bound to gravity the way humans are. They technically do not need to swim in one particular way and could have chosen to swim in either of the orientations.

In fact, technically speaking, fish should find it easier to swim upside down. The tops of the fish are usually heavier! However, fish continue to swim in the “right orientation”.

Why do fish swim with the “right” side up?

It is important to understand why fish prefer to swim in this way despite theoretically being able to swim both ways. The answer comes down to evolution.

During the earlier stages of evolution, the brain and eyes had to be placed on the “top” of the body to allow for quicker nerve communications. Naturally, mouth placement was under the body.

This was what lead to the fish choosing to swim in that way. If the fish were to swim upside down, they would be very disadvantaged. The eyes being below the mouth would mean that the food debris would get in their eyes as they ate. Similarly, it would mean that spotting predators would be a lot more difficult.

Thus the fish choosing to swim in this orientation can be attributed to evolution.

Another important advantage of swimming in the right way up that has been identified comes in the form of maneuverability. With heavier tops, fish will find it much easier to be able to change their directions, which can be extremely helpful to them.

For the most part, though, the choice comes down to what the fish are used to. For most fish, there is simply no advantage in swimming upside down, and they thus continue swimming the way that we have seen fish throughout our lives: the “right” side up.

Do some fish still swim upside down? 

Despite the evolutionary advantage the fish might have while swimming the right side up, some fish do resort to swimming upside down. The examples of these fish show how easy it is for fish to change their orientation if there were a need to.

The most prominent example comes in the form of fish that live at the reef or near piers. These structures tend to act as a cover for the fish and can put them in a state of ease.

Under such a cover, fish have been noted to swim upside down. They let their bellies rest against the structure, which ensures that they are not exposed to any predators. With the fear aspect removed, they tend to quickly swim upside down very comfortably.

However, when they leave the areas that have such structures, they immediately turn them right side up, and would not swim upside down in the open.

Another important example comes in the form of a catfish. Due to the behavior that it exhibits, a certain type of African Catfish has been named as the upside-down Catfish. The fish tend to swim upside down.

The fish have started to swim this way because the water at the surface of their habitat has higher oxygen levels. With their mouths at the bottom, these fish simply started swimming upside down to allow them to reach that oxygen.

This again goes to show that fish can easily swim upside down, but have no evolutionary advantage in doing so!

Is it concerning if my fish is swimming upside down?

Now that we have looked at the reasons that a fish may be swimming upside down, you might be wondering if a fish’s swimming upside down is a cause of concern. In that case, the first course of action for you would be to determine if your fish swims upside down as normal behavior.

Upside down catfish tend to swim upside down as a normal part of their behavior. Their swimming in that manner is not concerning. Similarly, lionfish tend to prefer swimming at odd angles, and might even swim upside down. This should not be a concern for you.

If any other of your fish is swimming upside down or floating upside down, then it might mean trouble though. Fish do not normally choose to swim that way. Fish might be swimming that way due to damage to their swim bladder.

The swim bladder helps a fish control buoyancy, and any damage to it can result in a fish swimming at odd angles and upside down. You should first try to determine if your fish seems to have trouble staying upright.

If the fish seems to have trouble remaining upright, you should try to find out what caused the damage. This can usually be a result of fights or of disease. A professional might be able to assist you better since damage to the swim bladder can be critical.

However, if the fish seems to be able to swim normally, then you can rule out the disease.

Conclusion

Fish are wonderful creatures and can swim in a number of ways. Despite that, they choose to remain on the right side up and swimming forwards.

I hope that this article helped you learn more about your fish and the many wonderful things that they can achieve!

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