How Do Ray-Finned Fish Keep From Sinking?

A common question we receive at the aquarium is “How do ray-finned fish keep from sinking?” Here is a blog post that will answer that question!

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Fish that live in water must have some way of countering the force of gravity or they would sink. In most fish, this is accomplished by a swim bladder, an air-filled sac that helps the fish maintain its position in the water column. However, not all fish have a swim bladder. Some, like ray-finned fish, have lost this evolutionary adaptation and must find other ways to keep from sinking.

So, how do ray-finned fish stay afloat? The vast majority of them accomplish this feat by using their fins to generate lift. By whipping their tails back and forth, they create a vortex of water behind them that pushes them forwards. This method of swimming is extremely energy-efficient, but it does have its limitations. Fish that rely on their fins for lift cannot swim very fast and they cannot maintain a stationary position in the water column. Consequently, they are often easy prey for predators.

Other ray-finned fish have evolved different strategies for combating gravity. Some species, like lungfish and bichirs, have retained primitive lungs that allow them to breathe air directly from the atmosphere. This adaptation gives them a significant advantage over their finned counterparts when oxygen levels in the water become low. Other species, like tetras and African lungfishes, have developed extra large fins that help them to stay afloat.

No matter what strategy they use, all ray-finned fish have one thing in common — they must constantly be moving to stay afloat. So next time you see a fish swimming lazily in an aquarium, take a closer look. You may just be witnessing one of nature’s most fascinating survival adaptations!

The Physics of Fluid Dynamics

Fish are able to swim in water because their body shape creates a small wake as they move through the water. This is due to the fluid dynamics of water. The main force that fish use to swim is called thrust. This is the force that moves the fish forward through the water.

Archimedes’ Principle

One of the most fundamental laws governing the behavior of fluids is Archimedes’ Principle. This principle states that a fluid at rest will exert an upward force on a body placed in it, equal to the weight of the fluid that is displaced by the body. Fluids include both liquids and gases.

This upward force is referred to as thebuoyant force. An object will float if the buoyant force exerted on it by the fluid is greater than its weight. The buoyant force is also responsible for keeping objects submerged in a fluid from floating to the surface.

The buoyant force depends on two things: the density of the fluid and the volume of the object that is submerged in the fluid. The denser the fluid, the greater the buoyant force. The greater the volume of an object that is submerged in a fluid, the greater the buoyant force.

Bernoulli’s Principle

In fluid dynamics, Bernoulli’s principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid’s potential energy. The principle is named after Daniel Bernoulli who published it in his book Hydrodynamica in 1738.

Bernoulli’s principle can be applied to various types of fluids, including liquids and gases. In fact, it is one of the most important principles governing the behavior of fluids. It explains, for example, how airplanes are able to fly and how fish are able to swim.

The Bernoulli principle is based on the conservation of energy. In a closed system (such as an airplane), the total amount of energy remains constant. This means that if one form of energy increases, another must decrease by an equal amount.

For example, if the speed of a fluid increases, its kinetic energy must increase. Since there is no other source of energy in the system, this increase in kinetic energy must come at the expense of the fluid’s potential energy. This decrease in potential energy manifests itself as a decrease in pressure.

How Ray-Finned Fish Use Fluid Dynamics

All fish have a problem. They are constantly fighting a battle against gravity, which wants to pull them down into the depths of the ocean. To combat this, fish have evolved a variety of strategies. One such strategy is seen in ray-finned fish, who have adapted their bodies to take advantage of fluid dynamics. In this article, we will explore how ray-finned fish use fluid dynamics to keep from sinking.

Lateral Line System

One way that ray-finned fish keep themselves afloat is by using their lateral line system. The lateral line system is a set of pores and canals running along the length of a fish’s body. These pores are connected to sensory cells that can detect changes in water pressure. By using their lateral line system, fish can sense when they are starting to sink and adjust their body position accordingly.

The lateral line system is just one of the many adaptations that allow ray-finned fish to live in a wide variety of environments. Their streamlined body shape and flexible fins give them the ability to swim quickly and maneuver easily in the water. Their respiratory and circulatory systems are also well-suited to life in the water, allowing them to extract oxygen from the water and circulate it throughout their bodies. Together, these adaptations make ray-finned fish one of the most successful groups of animals on Earth.


When a fish moves through the water, the fins help to stabilize and balance the fish. The fins also help the fish to change direction. Some fins, such as the dorsal fin, are used for protection. The average fish has two pairs of dorsal fins. The first is called the adipose fin and the second is called the ray fin. The ray fin is made up of many small bones called rays. The adipose fin is a fleshy fin that does not have any rays.

Some fishes also have a third dorsal fin. This third dorsal fin is located in the middle of the back and is often very small. This small dorsal fin is called a nuchal hump or nuchal crest.

The anal fin is located on the bottom of the fish near the tail. This fin helps to stabilize the fish when it swims. The pectoral fins are located on each side of the fish near the head. These fins help the fish to change direction when it swims. The pelvic fins are located on each side of the fish near the bottom of each side of its body. These fins help to stabilize the fish when it Swim


It’s really no mystery how ray-finned fish keep from sinking — their bodies are specifically designed for buoyancy. By distributing their body weight evenly and keeping their center of gravity low, ray-finned fish are able to float effortlessly in water. So next time you’re wondering how those little guys stay afloat, just remember — it’s all in the design.

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