What is the first fish to be on earth?

It's impossible to say definitively what the first fish was on Earth. The fossil record is incomplete, and the earliest fish-like creatures lived hundreds of millions of years ago.

However, we can look at some of the earliest known fish fossils to get an idea of what they were like:

* Pikaia: This creature, dating back to about 505 million years ago, is considered a possible ancestor of vertebrates (animals with backbones), including fish. It had a segmented body and a notochord (a flexible rod that supports the body), which are key features of vertebrates.

* Haikouichthys: This creature, from around 525 million years ago, is considered a very early fish-like creature. It had a head, a tail, and a series of gill slits, suggesting that it could breathe underwater.

* Myllokunmingia: This small, eel-like creature, also from around 525 million years ago, has been interpreted as one of the earliest true fishes. It had a skull, a braincase, and a series of paired fins.

It's important to remember that these are just a few of the many early fish-like creatures that have been discovered. The exact relationships between these creatures and how they evolved into modern fish are still being debated by scientists.

So, while we can't say for certain what the first fish was, we can appreciate the incredible diversity of life that has evolved over millions of years, starting with these early pioneers of the aquatic world.