He stares at fish. And all day and all night, and everything he sees is just food

Imagine how the fish feels

ₒₕ yes

Ikr? This isn't healthy or a happy environment for them - even the little Bettas

Are they not supposed to be kept in small tanks?

It's not healthy for any fish to be kept in a bowl at all
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As for tank size, largely debatable. Betta live in rice paddies in the wild. Which are very shallow - but very vast - bodies of water. They end up in puddles sometimes and have adapted to survive this, but it's not really ideal
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This bowl has absolutely nothing a betta needs beyond water