Further Research
Structure and Function of the Swim Bladder:
The swim bladder is usually formed of two gas-filled sacs located in the dorsal portion of the fish, although in more primitive species there is only one sac. Evolutionarily homologous to the lungs, the swim bladder has flexible walls which can contract or expand according to the ambient pressure. Its walls are lined with guanine crystals, causing them to be impermeable to gases. By adjusting the gas pressuring organ using the gas gland, the fish can achieve neutral buoyancy and thus ascend and descend to a range of depths. As a result of the dorsal positioning, the swim bladder also gives the fish lateral stability. The gas/tissue interface at the swim bladder produces a strong reflection of sound which is used in sonar equipment to find fish.
The swim bladder is usually formed of two gas-filled sacs located in the dorsal portion of the fish, although in more primitive species there is only one sac. Evolutionarily homologous to the lungs, the swim bladder has flexible walls which can contract or expand according to the ambient pressure. Its walls are lined with guanine crystals, causing them to be impermeable to gases. By adjusting the gas pressuring organ using the gas gland, the fish can achieve neutral buoyancy and thus ascend and descend to a range of depths. As a result of the dorsal positioning, the swim bladder also gives the fish lateral stability. The gas/tissue interface at the swim bladder produces a strong reflection of sound which is used in sonar equipment to find fish.
Which kinds of fish have swim bladders?
Swim bladders are found in many bony fish but are not present in cartilaginous fish. There are two types of fish with swim bladders:
1) those with Physostomous bladders - the swim bladder is connected with the gut, allowing the fish to fill up the swim bladder by 'gulping' air
2) those with Physoclistous bladders - the bladder is not connected to the digestive tract and thus the Physoclists have to do all their air volume changes using the circulatory system and a network of vessels called the rete mirabile
Swim bladders are found in many bony fish but are not present in cartilaginous fish. There are two types of fish with swim bladders:
1) those with Physostomous bladders - the swim bladder is connected with the gut, allowing the fish to fill up the swim bladder by 'gulping' air
2) those with Physoclistous bladders - the bladder is not connected to the digestive tract and thus the Physoclists have to do all their air volume changes using the circulatory system and a network of vessels called the rete mirabile
How is the swim bladder similar to a submarine ballast tank?
It is clear that the structure and function of the swim bladder has greatly influenced the construction of the submarine ballast tank as there are many similarities between them. However, there are also some major differences.
When a fish rises in the water column, it can excrete gas into the swim bladder, increasing its air volume and buoyancy and thus enabling it to rise. Analogously, when a submarine wishes to rise, it forces pressurised air into its ballast tanks, displacing water and therefore allowing it to rise. The difference here is that the fish does not displace water and simply expands the volume of gas (usually oxygen) in its air bladder.
However, they work very differently in their descents. When a fish descends, the gases in the swim bladder are either absorbed back into the blood or released through the gut (like a burp or fart). In both cases, the swim bladder decreases in size and buoyancy. Meanwhile, in order to dive, a submarine very differently floods its ballast tanks, replacing the buoyant air with non-buoyant water, thus causing it to sink.
This image shows how a submarine's ballast tank is like a fish's swim bladder:
It is clear that the structure and function of the swim bladder has greatly influenced the construction of the submarine ballast tank as there are many similarities between them. However, there are also some major differences.
When a fish rises in the water column, it can excrete gas into the swim bladder, increasing its air volume and buoyancy and thus enabling it to rise. Analogously, when a submarine wishes to rise, it forces pressurised air into its ballast tanks, displacing water and therefore allowing it to rise. The difference here is that the fish does not displace water and simply expands the volume of gas (usually oxygen) in its air bladder.
However, they work very differently in their descents. When a fish descends, the gases in the swim bladder are either absorbed back into the blood or released through the gut (like a burp or fart). In both cases, the swim bladder decreases in size and buoyancy. Meanwhile, in order to dive, a submarine very differently floods its ballast tanks, replacing the buoyant air with non-buoyant water, thus causing it to sink.
This image shows how a submarine's ballast tank is like a fish's swim bladder: