「魚 (さかな)」 means "fish." This word refers to a cold-blooded animal that lives in water, breathes with gills, and usually has fins and scales. You use it when talking about eating fish or seeing fish in the sea.

水中(すいちゅう)に住(す)む動物(どうぶつ)です。魚(さかな)を食(た)べます。