I thought it was proven they have about a three second memory. Even if memory could last a minute or two, I cannot fathom (no pun intended) how they remember anything long enough to be depressed, or happy for that matter.
That said, I would expect most pet owners (fish owners especially) would say that their time around the animals has led them to believe the animals do in fact have depression, joy, etc. On fish, I can only speak to the 15 or so we went through with my daughter. Specifically, there was a beta that she had that would watch me enter the room and keep watching me wherever I went. I'm pretty sure he was pissed off, and rightfully so, as we later discovered my daughter had not fed the fish. I'm not talking about skipping a meal, I mean she lost the fish food and rather than tell us, this 8yr old girl lied her arse off. We lost a dozen fish and couldn't figure out why - even water pH testing came back fine, so we didn't understand what was happening. The beta was the last one she had, by the time we figured out what she was doing I tried to feed him and he wouldn't even look at the food. Next morning he spent half a day in death twitches before giving in.
I'll never forgive her such cruel treatment of animals (I know she was just a kid). And I'll never forget the way that fish looked at me for the days leading up to his death.