Yes zoos do make animals depressed since the animals who are in the zoo have no freedom to run around in the wild like they used too.
I used to work in a zoo and the workers at the zoo including myself took really good care of the animals and we loved those animals and did our best to give them the best life they could have in the zoo.
But I could tell myself that the animals were seeming depressed because they were locked in a zoo and I could do nothing to release those animals from the zoo even though I had wished I could.
I eventually left the zoos I was working for because although I loved the job and being around the animals in the zoo I couldn't stand to see there sad faces especially when no one else was around visiting them.
Animals might seem happy when visitors to the zoo are around but behind the scenes animals in zoos are depressed and really animals should not be living in zoos which really are prisons for innocent animals.
I think we need to release the animals to the wild where they belong to have freedom and we need to close down zoos and stop visiting the zoos.