Saltwater Fish
noun
You've got a sea water fish, or in other words, a saltwater fish.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
カクレクマノミは海水魚です。
The clownfish is a saltwater fish.
このお店で一番人気のある海水魚はどれですか？
Which is the most popular saltwater fish in this store?
やっぱり海水魚はニオイが気になります。
After all, I'm worried about the smell of saltwater fish.