• 金魚きんぎょ — goldfish
• 人魚にんぎょ — mermaid
• 魚屋さかなや — fish shop
• 海魚かいぎょ — ocean fish
• 熱帯魚ねったいぎょ — tropical fish
• 魚類ぎょるい — fish species

魚 is a pictographic character that resembles the shape of a fish, with fins and tail. It directly represents "fish" and is frequently used in words related to seafood, species, and fishing.

魚さかなを食たべるのが好すきです。
I like eating fish.

金魚きんぎょが 泳およいでいます。
The goldfish is swimming.