Here's why:
* Swim bladders are buoyancy control organs. They allow fish to adjust their position in the water column.
* Bottom-dwelling fish don't need to adjust their buoyancy. They live on the seabed and don't need to rise or sink.
* Instead, they rely on other adaptations for their lifestyle. They often have flattened bodies and strong fins for maneuvering along the bottom.
Some examples of bottom-dwelling fish without swim bladders include:
* Flounders
* Soles
* Rays
* Sharks
While some exceptions exist, like the anglerfish, which has a reduced swim bladder, the general rule is that bottom-dwelling fish do not have them.