Fishes on the move Body and fins shape: not all fishes are swimming in the same way

In the liquid element, movement is influenced primarily by the resistance of the mean, which is eight hundred times greater than the air. Something not of little importance. Any diver will immediately notice the resistance he encounters in moving into water.

That said, think about fishes: they are tied to that world and their movements are strongly influenced by the water, that is from the liquid element density. This premise to cover a whole series of peculiarities relating to swimming of animals such as fishes which, over time, have evolved on the planet developing a range of more than satisfactory solutions, in function of different habitats and life choices.

When men faced for the first time the problems of hydrodynamics, took cue from fish movements. Their tapered shape and the way they swim are always aimed to achieve maximum results with minimum effort. Based on the dietary needs and habits of life, fishes species have each developed a different way of moving. Needless to say, the fishes most skilled and fast in swimming are those having an aspect closest to fusiform, i.e., tunas and sharks. Even the most of the other fishes are close to this classic form, but there are many situations and environments which see fishes with strange shapes, sometimes very little suitable for a quick swim and anything but hydrodynamic.

However, even a flounder, flat and adapted to the sandy bottom, or a tub gurnard, with wing-like fins and singular swimming, become some of the many xamples that show how various is the fishes’ way of swimming in the wild, and how some species remain even motionless, moving only occasionally in function of precise needs.

It’s a fact, then, that not all fishes are swimming in the same way, and one of the most important things to consider is the shape of the body and fins. The observations on the spot, a privilege of those who dive in a conscious way to observe, study and understand while photographing, allows us to reach out and touch many peculiarities of the movement and to grasp the differences between one species and another. If we take a series of pictures in sequence (even better a video), we realize that the movement of a fish is the result of a series of flexion of the body and is primarily generated from the tail.

Different type of  fish shape and fins

The side muscles are the engine and thus the fishes with well-developed muscles are those most powerful and fast in swimming. Nevertheless, fishes also need other movements beyond the forward propulsion: they need to back off, to make a turn and always face different situations with ease. For all these movements, different from proper propulsion, the fins come into play. Knowing the fins becomes important to understand what they are for, how they are used and what kind of movements are possible depending on the shape and size of the fins themselves.

Practical experience and direct observations in the wild lead me inevitably to use some examples to better explain some concepts. If we observe a grouper, a fish who loves different environments and is lazy swimmer, with exceptions, we immediately understand that its passion is to linger and observe what is happening around, maintaining a stable position in open water.

To do so, it mostly uses its large rounded pectoral fins and partly the dorsal and anal fins, as well as the tail (the fin that perhaps is the most important of all). In case of doubt or signs of imminent dangers, groupers bring the pectoral fins along the sides, and with strong movements of the tail perform rapid shifts, with a significant propulsion linked to the remarkable size of the caudal fin. Many serranids move in this way and, in large groupers, the sudden movement of the tail generates a displacement of water masses perceptible by the diver. The grouper maintains a fusiform body shape, even if it has a head larger than the rest of the body, and despite its lazy nature, it’s an excellent swimmer.

Otherwise, there are fishes such as scorpion fish or stonefish, whose form is squat and stocky, very lazy and listless swimmers. However, they have large pectoral fins and large tails, which allow rapid and jerky movements in case of danger and amazing turns, with sudden changes of direction. Watching them is a unique experience especially when, tired of our presence in the area, they rise laboriously to swim toward more peaceful places. Another particularly static fish is the frogfish, with pectoral fins that look almost real limbs (similar to frog’s legs, to be precise).

Different type of  fish shape and fins

Funny in the appearance, this little fish moves very slowly and seems as if it is walking instead of swimming. But in terms of absolute laziness, the winner is the seahorse, the only fish with virtually nonexistent tail fin, replaced by a prehensile tail, used as if it was the tail of a chameleon, for a secure grip to various handholds on the seabed. The seahorse swims very rarely and to do so uses the dorsal fin and the frantic and small pectoral fins. However, his life is very static, which allows you to observe it for long periods and to photograph all situations with ease.

With the mouth similar to that of a seahorse, but constantly moving in open water, there are the rather small Mediterranean trumpet fishes, always passionately together to form schools of many individuals, capable of frantic movements and skilled in a unique swimming style upside down. Anyone who has observed the environments of coral reefs will have then noticed the unusual shape of butterfly fishes, so called because of the shape and bright colors, decent swimmers but never too fast. Another example of how the body shape and fins are the key in the study of fish movement. Even the triggerfishes swim in a curious way: in principle, they exploit the dorsal and anal fins, very similar and counter-posed in comparable position, with which they perform these continuous waving movements, allowing the fish grand maneuvers and quick changes of direction.

In open water always swim the fastest fishes, such as many representatives of breams and wrasses and several species of pelagic, including amberjacks, tunas, dorado, marlin, sailfishes and, of course, sharks. All fishes with big fins and very powerful tails. Returning to the benthic species, the primacy of the more curious swimming style is for blennies, small fishes without scales very curious and friendly, tapered and with almost eel-like swimming style. Observing the blennies making small movements around the bottom, to which they are inextricably linked, is a unique spectacle. In particular, the big Mediterranean butterfly blenny deserves a special mention for being one of the few blennies able to swim in open water and deal decisively with divers, especially during the brooding of the eggs.

There are then a whole series of fish with fins in the shape of wings. Beautiful fins that serve to glide in the vicinity of sandy bottoms. The tub gurnard, but also the owl fish, keep these large extremities generally closed, opening them only when they need to move over long distances. In fact, they generally love moving slowly, preferring contact with the seabed, according to their continuous wandering in search of food. The observation of the fish swimming would deserve constant attention and constant study. There are not enough words to describe what is happening under the eyes of the attentive diver.
Nevertheless, maybe some pictures can tell about what amazing spectacle the sea is.

WORDS and PICTURES by Francesco Turano

Different type of  fish shape and fins

Bookmark the permalink.

Comments are closed.