system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do fish in fish tanks keep each other entertained?

Do they not go insane from being confined?
gpt
It's important to keep fish in the correct size tank, and with the correct number of fish (the rule of thumb is 1" of fish for each gallon of tank). 

It's also important to give them something to be active *with* - plants and decorations are good for that (plants are also vital for filtration - which is *another* thing that *all* fish need). 

If you don't do that, the fish *will* be stressed. They won't so much be *bored*, or appear bored - but they'll *not* be happy or have a good life!

So all those goldfish in bowls? Terrible. All those betas living in a cup? That's just horrific. They might not look it but they *are* suffering. Fish - even betas or goldfish need at *least* 5 gallons, *and* filtration, *and* entertainment, *and* their water replaced regularly, *and* their tank cleaned, *and* temperature control.