Why does a fish have more vertebrae than other vertebrate animals?

That's not entirely true! Fish don't necessarily have more vertebrae than other vertebrates, but they often have more vertebrae than mammals or birds. Here's why:

* Body Shape: Fish have long, streamlined bodies designed for swimming. This requires a flexible spine, which is achieved by having many vertebrae.

* Locomotion: Unlike land animals that use legs for locomotion, fish use their bodies and tails for swimming. This requires more segments (vertebrae) to create a powerful wave-like movement.

* Evolutionary History: Fish evolved before land animals, and their body plan reflects this. Over time, land animals have evolved more compact vertebral columns as their movement and support needs have changed.

Exceptions:

* Eels: Eels are an example of fish that do have a very high number of vertebrae, sometimes over 100! This allows for their extreme flexibility and serpentine movement.

* Amphibians: Some amphibians, like salamanders, also have a large number of vertebrae due to their elongated bodies.

In summary:

It's not about fish having more vertebrae than *all* vertebrates, but rather a higher number of vertebrae compared to some other groups, due to their unique body shape, locomotion, and evolutionary history.