- Oasis Aquarium
- Oi Ah Kaw
- Olympia Aquarium
- One Stop Aquarium
- Oriental Aquarium (S) Pte Ltd
- Oceanwide Marine Aquarium
- Ong Chin Soon
- Ong's Tropical Fish Aquarium & Fresh Flowers
- Outram Marketing Services
- Oasis Aquarium
- Oi Ah Kaw
- Olympia Aquarium
- One Stop Aquarium
- Oriental Aquarium (S) Pte Ltd
- Oceanwide Marine Aquarium
- Ong Chin Soon
- Ong's Tropical Fish Aquarium & Fresh Flowers
- Outram Marketing Services