A fish is a water-dwelling animal with gills that breathes through them and has a backbone, fins, and a two-chambered heart. If you’re the inquisitive type, that may be all you need to know about them – aside from whether they go better with cocktail or tartar sauce. But for those of us who like fish, they’re utterly fascinating creatures about which we can’t get enough information.
They range in size from small creatures that would fit on a fingernail to monsters the size of a cabin cruiser. They have the ability to sleep with their eyes open, taste without using their mouths, and float without casting a shadow.
The ability of a fish to swim backward is probably not something that many fish keepers have given much thought to. After all, there are very few situations, especially in the wild, in which a fish would be expected to do so. Swimming forward is unquestionably the preferred direction of fish, with the occasional hovering thrown in for good measure.
Can fish swim backwards?
The large majority of fish swim forward, but the majority also have the capabilities to swim backward. Fish that swim backwards are typically species that use anguilliform (eel-like) locomotion to move their elongated bodies. The gobies are a great example of this.
That doesn’t mean that fish can’t swim backwards. In fact, I know they can because I’ve seen it with my own eyes. I have a very shy Frontosa Cichlid who swims backwards into his cave slowly whenever I approach with his food.
Unfortunately, he does not swim backwards gracefully, and I’m confident that if he had to do it for more than a few inches, he would struggle. He is, however, not the only species of fish that can swim backward, and he is far from the best.
Fish That Swim Backwards Well:
Fish that swim backwards the best are typically species that use anguilliform (eel-like) locomotion to move their elongated bodies. They are able to do so because their entire body is flexible along its entire length. The movement is in the form of a sinuous wave that runs from head to tail.
It has also been discovered that electric fish can swim backwards as well as forwards. For example, black ghost knife fish swim backward by swirling the fin on their belly. They do this so they can swim over prey species, scan it with their electroreceptors, and then lunge at it without having to turn around. If they swam forwards, their prey would end up by their tail and they would be unable to eat it.
Other Forms Of Swimming:
Of course, not all fish use anguilliform locomotion or are as adept at swimming backward as eels and electric fish. There are many other types of locomotion, which are discussed further below.
Fish with a stiffer body and greater speed, such as trout, use sub-carangiform locomotion. It works by increasing wave amplitude along the body, with the rear of the fish doing the majority of the work.
Carangiform locomotion is a movement originating from a fish’s posterior. This means that in carangiform locomotion, only the back half of the body vibrates with the passage of contraction waves. Carangiform locomotion is commonly used by fish such as Jacks, Pompanos, Mackerel, runners, and scads.
Carangiform locomotion is considered to be the most effective way of swimming, though it is not necessarily related to fish swimming backward. This is because it is how the majority of the fastest and most active fish swim.
Thunniform locomotion is used by a class of fish that includes fast and long-distance swimmers like tuna and many lamnid sharks. Almost all sideways movement occurs in the tail and the space linked to it, known as the peduncle. These fish’s tails are typically large and crescent-shaped.
Ostraciiform locomotion is a type of fish movement in which only the caudal fin rotates from side to side, similar to moving a boat with one oar. Boxfish, cowfish, and trunkfish all swim in this way to prevent predators, and despite this, they are amazingly good backward swimmers.
Fish That Can’t Swim Backwards:
The shark is the only fish that we are certain is totally incapable of swimming backward. This is due to the fact that their pectoral fin cannot bend upwards like a fish’s. Sharks, unfortunately, can only move forward, though they can sink back slightly by using gravity. Not related, but just so you know, sharks cannot simply stop if they need to prevent colliding with something. To prevent a collision, they must instead swerve to the side. It’s strange, considering sharks are apex predators, that they would have swimming or movement limitations.
There is also some debate about the ability of seahorses, Razorfish, and shrimp fish, which all swim vertically, and large fish such as marlin, tuna, and Arowana to swim backward.
Can Fish Swim Backwards For Long?
It’s difficult to imagine a fish having to swim backward for an extended period of time, so whether they can or can’t is a moot point. However, for the sake of curiosity, we will address it.
You may have heard stories about sharks being dragged back through the water and drowning as a consequence. This is not only cruel, but it is also inaccurate. A shark pulled backward through the water would suffocate rather than drown because breathing would be extremely difficult.
The shark would suffer to breathe because water must flow over its gills in the correct direction for them to function. For fish, this is accomplished by water passing through the mouth and out of the gills. Pulling them backwards reverses this process, making it extremely difficult for them to breathe.
Curiously, when catching large fish like tuna and marlin, fishermen have been known to use backward pulling to belt them out. They compare this experience for the fish with us wearing an elevation mask and then vigorously exercising. You can still breathe, it’s just a little more difficult.
It is difficult to imagine a fish choosing or being capable of swimming backward for long distances.
Why do electric fish swim backwards?
Electric fish can frequently swim backwards as well as forwards. Such fish can recognize their prey’s characteristic electric fields by swimming backwards (Environmental Biology of Fishes, vol 36, p 157).
Several fish species have evolved the capacity to generate electrical pulses from specialized ‘electric organs’ derived from muscle or nerve tissue. Some fish, like the electric ray (Torpedo nobiliana), stun their prey with massive electrical discharges, while others sense their surroundings with a steady stream of weak pulses – sometimes more than 1000 a second.
The weak pulses travel outward through the water before returning to the electric organ via thousands of conductive pores covering the fish’s body. Under the pores, which are most densely packed on the head, are ‘electroreceptors,’ which contain cells that are sensitive to electric pulses and are linked to the brain via nerve fibers. Objects in the water distort the electric field emitting from the fish, causing the pulses returning to the electroreceptors to be altered. The fish sense their surroundings in this way.
This sensory system evolved separately in two groups of freshwater fish – the electric eels and knife fish of South America and the elephant snout fish and one similar species in Africa – in a remarkable case of convergent evolution. Strictly speaking, both groups of fish have a ‘active’ electric sense. Other fish have a ‘passive’ electric sense, which detects only external sources of electricity, such as those associated with water currents.
Surprisingly, almost all fish with an active electric sense can swim backwards. The Amazon basin’s turbid waters are home to the black ghost fish, which has poor vision. It uses an active electric sense to hunt for plankton and other small prey.
The fish approaches the tail of the likely prey first. It swims backwards by rippling the elongated fin on its belly, staying close to the prey at all times. Only when the prey is directly in front of the fish does it strike with a forward lunge.
According to the researchers, the fish swims past objects in order to scan them with its electroreceptors. Because an electric sense cannot be concentrated like an eye, this is the only way the fish can recognise prey. However, if the fish scanned by swimming forward, the prey would end up at its tail. To be able to eat the food, the fish must swim backwards.
Almost every fish, with the exception of the shark, appears to be capable of swimming backwards if necessary or desired. It’s difficult to believe, though, because it makes breathing more difficult and exhausting for them to do so frequently. Backward swimming appears to be used for survival purposes, such as preventing predators or, in the case of electric fish, catching them.