What animals are fish?

This is a bit of a trick question! It depends on how you define "fish."

Scientifically speaking:

* Fish are a diverse group of aquatic vertebrates that belong to the class Actinopterygii (ray-finned fishes) and class Sarcopterygii (lobe-finned fishes). This means they have a backbone, gills for breathing underwater, and typically fins for movement.

Commonly, people think of:

* Fish as aquatic creatures that have scales, fins, and live in water. This includes a variety of species, like salmon, tuna, sharks, and even eels.

However, some creatures that are commonly called "fish" are not actually fish in a scientific sense:

* Jellyfish: are not fish! They are invertebrates (no backbone) and belong to the phylum Cnidaria.

* Starfish: are also not fish! They are invertebrates belonging to the phylum Echinodermata.

So, while the term "fish" is often used broadly, it's important to remember the scientific classification and that not all creatures we call "fish" are actually members of the class Actinopterygii or Sarcopterygii.