Final answer:
Fish are composed of solid materials, as evidenced by their cells, tissues, bones, and organs. Despite living in water, they aren't liquid and they maintain a definite shape and volume.
Step-by-step explanation:
Fish, like other organisms, are made up of solid material. They are made of various complex cells, tissues, bones, and organs that are solid in nature. If you touch a fish, you'll feel its solid body structure. Although fish live in a liquid environment (water), they are not liquid themselves. They don't change shape freely to match their container like a liquid would, nor do they fill up a space like a gas. Instead, they maintain a definite shape and volume, characteristics of a solid matter.
Learn more about State of Matter