Why are my fish swimming at top of tank?

Related questions

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2. Why does my fish stay at top of tank?
3. Can I bring a backpack into Shedd Aquarium?
4. Whats the biggest aquarium in the world?
5. Does Boston have an aquarium?
6. Why is my fish gasping for air at the top of the tank?
7. What fish lives the longest for a pet?
8. What is the main purpose of aquariums?
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Tags

1. #gasping
2. #suffering
3. #doesn
4. #swimming
5. #enough
6. #occur
7. #oxygen
8. #needs
9. #dissolved
10. #hypoxia
11. #surface
12. #appears