O
- Oarfish
- Ocean perch
- Ocean sunfish
- Oceanic flyingfish
- Oceanic whitetip shark
- Oilfish
- Oldwife
- Old World knifefish
- Old World rivuline
- Olive flounder
- Opah
- Opaleye
- Orange roughy
- Orangespine unicorn fish
- Orangestriped triggerfish
- Orbicular batfish
- Orbicular velvetfish
- Oregon chub
- Oriental loach
- Owens pupfish
Read more about this topic: List Of Common Fish Names