Why is my betta fish building a bubble thing on top of its fish bowl?

Why is my fish building a bubble thing on top of its fish bowl? I heard the word "bubble nest" a lot in other questions. What is a bubble nest and what is a bubble nest do or what is it for? Because that might be what my betta fish is doing! And should I worry about my betta fish? He is a male and his name is... show more Why is my fish building a bubble thing on top of its fish bowl?
I heard the word "bubble nest" a lot in other questions. What is a bubble nest and what is a bubble nest do or what is it for? Because that might be what my betta fish is doing! And should I worry about my betta fish? He is a male and his name is Aqua.

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