Refers to fish that live in saltwater. The term is less common than 海水魚 (かいすいぎょ) in everyday use.
Saltwater fish are more tolerant of salt than freshwater fish.
Freshwater fish, the opposite of 鹹水魚.
Compound of 鹹水 (saltwater) + 魚 (fish). 鹹 is a rare kanji meaning 'salty'.