Since this word is made up of a single kanji, it should use the kun'yomi reading. When learning the kanji, you didn't learn that reading, so here's a mnemonic to help you with this word:
Imagine a fish. Now imagine the fish playing soccer, while wearing a nun's outfit. This is a soccer nun (さかな).
I like fish, but I don’t like it raw.
I always eat granola and fish for a well-balanced breakfast.
I’ll never buy fish from the back of a pickup truck in Mexico again.